Judgment and Decision Making, Vol. 10, No. 1, January 2015, pp. 50–63
Psychological aspects of the rejection of recycled water:
Contamination, purification and disgust
Paul Rozin∗ Brent Haddad† Carol Nemeroff‡ Paul Slovic§
Abstract
There is a worldwide and increasing shortage of potable fresh water. Modern water reclamation technologies can
alleviate much of the problem by converting wastewater directly into drinking water, but there is public resistance to
these approaches that has its basis largely in psychology. A psychological problem is encapsulated in the saying of those
opposing recycled water: “toilet to tap.” We report the results of two surveys, one on a sample of over 2,000 Americans
from five metropolitan areas and the second on a smaller sample of American undergraduates, both assessing attitudes to
water and water purification. Approximately 13% of our adult American sample definitely refuses to try recycled water,
while 49% are willing to try it, with 38% uncertain. Both disgust and contamination sensitivity predict resistance to
consumption of recycled water. For a minority of individuals, no overt treatment of wastewater will make it acceptable for
drinking (“spiritual contagion”), even if the resultant water is purer than drinking or bottled water. Tap water is reliably
rated as significantly more desirable than wastewater that has undergone substantially greater purification than occurs with
normal tap water. Framing and contagion are two basic psychological processes that influence recycled water rejection.
Keywords: water, purification, contamination, shortage, disgust.
1 Introduction
Although the earth is a “blue” planet, an extremely small
proportion—well below 1%—of its total water endow-
ment presents itself as usable fresh water. This water
arrives annually as snow or rainfall, or is present year-
to-year as surface fresh waters, groundwater, or in living
biomass. Water plays fundamental and vital roles, con-
stituting over 50% of the weight of humans, as a funda-
mental requirement for all living creatures, and hence all
foods. Water is the most important nutrient, and lack of
water causes death more rapidly than the lack of any other
nutrient. Water technologies, developed over millennia,
have resulted in agricultural irrigation projects, and have
enabled the existence of modern cities. The intensity and
frequency of use of the earth’s fresh-water supplies are
growing, and major shortages exist already in places in-
cluding the Middle East, much of Australia, and the Amer-
ican Southwest. Indeed it has been claimed that wars in
the near future will be fought not over oil, but over wa-
ter (Lapping, 2011). Yet, nearly all of the technical prob-
The research presented in this paper was supported by a grant from
The WateReuse Foundation WRF–04–008, “Understanding the New Ur-
ban Water Customer.”
Copyright: © 2015. The authors license this article under the terms of
the Creative Commons Attribution 3.0 License.
∗Department of Psychology, University of Pennsylvania, 3720 Wal-
nut St., Philadelphia, PA 19104–6241. Email: rozin@psych.upenn.edu.
†University of California at Santa Cruz.
‡University of Southern Maine.
§Decision Research and University of Oregon.
lems of treatment and delivery of potable water have been
solved. In areas where project costs and technical issues
are tractable, the problem is now in large part psychologi-
cal: lack of acceptance of water produced by modern tech-
niques that cut the time and distance that would naturally
intervene between wastewater discharge and potable wa-
ter generation. This can now be accomplished directly by
on-site treatment of wastewater.
The informal or inadvertent reuse of urban wastewater
has been practiced throughout time. Historically, “down-
stream” users relied on the (imperfect) purification abili-
ties of natural systems (rivers, lakes, and aquifers) supple-
mented by their own treatment actions prior to consump-
tion. More recently, the discharging city has been required
to treat its wastewater before releasing it back into a nat-
ural system. And even more recently, as the need grows
for additional potable water and as treatment technolo-
gies have advanced, the planned reuse of urban wastew-
ater has expanded (NRC, 2012). Water treatment plants
are divided into four zones: primary treatment that phys-
ically separates wastes from water; secondary treatment
that uses friendly microbes to break down, remove, and/or
neutralize unwanted biological elements; tertiary treat-
ment that employs filters to remove additional unwanted
biological material; and advanced treatment that utilizes
membranes in pressurized vessels to remove nearly all
non-H2O biota and chemicals. A disinfection step is the
final treatment activity before water is released. Nearly all
facilities in the U.S. have primary and secondary systems,
which are required by law. A growing number have ter-
50
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 51
tiary and advanced systems, which constitute costly addi-
tional infrastructure, but result in almost completely pure
and safe drinking water. In this paper we refer to water that
has gone through at least the first three stages as “recycled
water.”
The public acceptance of water reuse is the topic of this
paper. In a democratic and litigious society, a committed
minority can drastically slow down institutional changes
that clearly serve the public good. In Singapore, a quasi-
democratic society, it is easier to ignore vocal minorities,
and recycled water has made great strides. Recent research
on acceptance of treated urban wastewater suggests that
recycled water acceptance is influenced by: 1) the words
used to describe the water (Menegaki et al., 2009); 2)
knowledge of treatment processes (Dolnicar et al., 2010),
and 3) level of trust in the purveyor of the water (Doria,
2010). Po, Moloney and Blair (2003) and Russell and Lux
(2006) review research on acceptability, focusing on the
Australian context. The focus in the present paper is on
understanding one theme that underlies opposition to re-
cycled water: the emotion of disgust and ideas of contam-
ination. Assurance that water is scientifically documented
as pure or uncontaminated is not sufficient for some adults.
The “toilet-to-tap” mantra of the opponents of recycled
water in the American Southwest can be powerful. It calls
upon our revulsion at waste, and our deep-seated intuitions
about contamination. This problem falls under what Paul
Slovic and his colleagues have called “intuitive toxicol-
ogy”, and raises complex issues of the assessment of risk,
including human feelings as part of the calculation of costs
and benefits, and the communication of risk (Kraus, Thob-
jorn & Slovic, 2002).
The fact is that all water is physically contaminated.
Our colleague, geologist Robert Giegengack, has calcu-
lated for us that it is impossible to drink a glass of water
in Europe without ingesting at least a few water molecules
that passed through the body of Adolf Hitler! (It takes
about 2,000 years for water to equilibrate around the earth,
which is why this does not hold for North America or other
areas distant from Europe. On the other hand, we are all
drinking Moses molecules when we drink a glass of wa-
ter.)
Some people are ready to accept recycled water, but a
minority resist it strongly (see reviews by Po, Kaercher &
Nancarrow, 2003; Russell & Lux, 2006). One presum-
able basis for this resistance is a reaction to the thought
of drinking water generated from urban wastewater. This
elicits the often powerful emotion of disgust, which causes
a feeling of offense and a behavioral withdrawal from the
relevant entity (Rozin, Haidt & McCauley, 2008). A re-
view of the literature on acceptance of recycled water sug-
gests that one component of rejection is disgust, or the
“yuck” factor (Po et al, 2003). The focus of disgust is a
reaction to spoilage and to bodily products (Rozin & Fal-
lon, 1987). These are, of course, major components of
urban wastewater.
Disgust is all the more salient and potentially problem-
atic because disgusting entities show magical contagion
properties. Around the turn of the 20th century, three
anthropologists (Frazer 1890/1959; Mauss, 1902/1972;
Tylor, 1871/1974) described the magical law of conta-
gion, a belief ascribed to “primitive” peoples but also be-
lieved to reflect a fundamental principle of human think-
ing. The magical law of contagion, or as we have come
to describe it, the intuitive contagion heuristic, holds that
“once in contact, always in contact.” That is, when two
entities come into contact, they exchange properties or
“essences”. The matter is of particular concern and im-
portance when one of the objects is disgusting. Thus, any-
thing that touches something disgusting becomes disgust-
ing. In the 1980s, Rozin, Nemeroff and colleagues showed
that magical contagion beliefs are widespread in Ameri-
can adults (Rozin, Millman, & Nemeroff, 1986; Rozin,
Nemeroff, Wane, & Sherrod, 1989). For example, if a
heat sterilized dead cockroach is briefly dipped into a glass
containing a previously desirable beverage, that beverage
becomes psychologically contaminated, and hence unac-
ceptable (Rozin et al., 1986). So far as we know, all
normal adults around the world show magical contagion
beliefs with respect to some contaminants. These beliefs
arise somewhere between four and six years of age (Fal-
lon, Rozin, & Pliner, 1984; Rozin, Fallon, & Augustoni-
Ziskind, 1985; Hejmadi, Rozin, & Siegal, 2004; Siegal,
1988). We have identified the magical law of contagion as
a cognitive heuristic, that is, a time and effort saving cog-
nitive rule of thumb which allows for rapid and generally
effective decision-making under conditions of uncertainty
that are characteristic of daily life (Nisbett & Ross, 1980;
Rozin & Nemeroff, 2002). Recent work by Callaghan,
Moloney, & Blair (2012) suggests, based on coded free
responses to the issue of water recycling, that contagion is
a major theme of concern for Australians. One can reason-
ably consider the “contagion heuristic” as a component of
a set of adaptations that effectively reduce the probability
of infection, designated as the “behavioral immune sys-
tem” by Schaller and Park (2011).
Analysis of contagion beliefs in adult Americans sug-
gest that there are at least two mental models of what is
passed when contagion occurs (Nemeroff & Rozin, 1994).
One, which we call material contagion, is conceived as
some sort of physical substance and hence can be neu-
tralized by some combination of washing, filtering, boil-
ing and other treatments. The other is spiritual contagion,
conceived of in terms of the entrance into the target of
some spiritual essence which does not resemble standard
physical entities. It does not respond to washing, boil-
ing or filtering, but remains as a permanent essence. An
example is the sports locker rooms at Pennsylvania State
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 52
University, which, following revelations of child abuse oc-
curring there, made student athletes feel “uncomfortable”
to use, and will be renovated (Associated Press, 2012).
If the sense of spiritual contagion can be cancelled at all,
it is with an opposite spiritual essence, as when Mother
Teresa wears Hitler’s sweater (Nemeroff & Rozin, 1994).
Most Americans carry both models of contagion in their
heads, generally applying material models to germs and
toxins, and spiritual models to moral offences. However,
some people operate with only a material model and oth-
ers with only a spiritual model, applied across all contam-
ination scenarios (Nemeroff & Rozin, 1994). The degree
of change in acceptability as a function of different purifi-
cations generally allows inference of whether one faces a
spiritual or material contagion model. It is important to
note that intuitive contagion can also be positive, i.e., that
the essence that is transmitted can carry positive features,
which is why Mother Theresa can in some cases cancel
out Hitlerness.
Four properties of magical contagion beliefs are par-
ticularly relevant to understanding water contamination
(Rozin et al., 1986, 1989; Nemeroff & Rozin, 1994; Ne-
meroff & Rozin, 2000; Rozin & Nemeroff, 2002).
1. Physical contact is necessary for contagion to be ef-
fective.
2. Permanence: Once magical contamination has oc-
curred, it tends to be permanent. Neither time nor spatial
distance reduce the effect substantially.
3. Dose insensitivity: Very brief contact with a disgust-
ing entity is sufficient to endow a target entity with disgust
properties.
4. Resistance of contaminated entities to purification.
This amounts to indelibility of contamination for some
contaminants and some individuals (Nemeroff & Rozin,
1994).
Clearly, these features bode badly for acceptance of re-
cycled wastewater, at least in the absence of some psy-
chological intervention. In this paper, we explore four hy-
potheses:
1. Disgust sensitivity is linked to rejection of recycled
water.
2. Contagion sensitivity is linked to rejection of recy-
cled water.
3. Reactions of most individuals to wastewater and var-
ious purifications are consistent with the basic fea-
tures of magical contagion.
4. For some people, waste contamination follows a spir-
itual model and hence is not purifiable by physical
means. These are the individuals who are most likely
to find recycled water unacceptable in spite of numer-
ous physical purification processes.
We explore, in two studies, the nature and importance
of disgust and contagion/ contamination beliefs in under-
standing the rejection of recycled water. Individual sen-
sitivity to disgust varies widely, and is usually measured
with the DScale (Haidt, McCauley, & Rozin, 1994), or its
modified version, the DS-R scale (Olatunji et al., 2007).
Unlike the case for disgust, there is no generally accepted
measure of contagion sensitivity. We develop a relevant
measure in Study 2. Also, since there are resemblances
between contamination sensitivity and obsessive compul-
sive disorder, we include a standard measure of the latter
in Study 2.
2 Study 1: Acceptability of recy-
cled water, related to contamina-
tion and disgust in a large sam-
ple of geographically diverse adult
Americans
In a large scale study (Haddad et al., 2009), we have ad-
dressed the psychological bases of rejection of recycled
water in reasonably representative samples of five Ameri-
can metropolitan areas, three of which experience chronic
water shortages. Study 1 reports a subset of the data col-
lected, relevant to disgust and contagion.
2.1 Method
Short surveys were distributed and collected in public
places, primarily train stations, at five cities around the
United States. There were 2,680 subjects, with 1297
(48.4%) female. Mean age was 37.93 years (SD =15.55),
and mean education was 14.77 years (SD=2.80). The
principal religions were Protestant (29.6%) and Catholic
(26.0%). The subjects were solicited from Phoenix,
Arizona (24.1%), San Diego, California (25.1%), San
Jose, California (16.0%), Eugene, Oregon (11.4%), and
Philadelphia, Pennsylvania (23.4%). For the California
and Arizona samples, a questionnaire in Spanish (trans-
lated and back-translated) was available to subjects who
preferred that language). Three of the metropolitan areas
(Phoenix, San Diego and San Jose) regularly experience
water shortages.
All of the questionnaires distributed were a single two-
sided page. The brevity is a consequence of the sam-
pling strategy, which aimed to obtain a broad cross-section
of the population; respondents were solicited while they
were waiting in train stations and other public places, and
so had relatively little time. Participation was rewarded
with an inexpensive automatic pencil or other “gift” val-
ued at about $.50. Completion took a few minutes. In
order to balance a large number of questions with the need
for brevity, there were seven forms of the questionnaire.
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 53
The first page was identical in all forms and included stan-
dard demographic information, and questions about will-
ingness to drink recycled water. The second page con-
tained different items for each form. Thus most questions
were asked of only 1/7 of subjects, 300–400 respondents
for each form.
A critical question about recycled water was asked of
all subjects, on the first page of all seven versions of the
survey:
“Recycled” water is water that is separated from
wastewater and highly treated so it can be used
again. It is also called “reclaimed water” and
“water reuse.” It has become an important po-
litical issue nation-wide, such as in the Ameri-
can west, where there is a shortage of “natural”
water, such as the Colorado River. Recycled wa-
ter has ecological and economic advantages over
other sources of water, but some people object
to its use as drinking water. This survey is an
attempt to understand the nature of this objec-
tion, and is part of a research program carried
out jointly by scientists at the University of Cal-
ifornia at Santa Cruz, the Universities of Penn-
sylvania and Oregon, and Arizona State Uni-
versity. The questionnaire is anonymous. Your
name does not appear on it.
Would you be willing to drink certified safe re-
cycled water?
NO UNCERTAIN YES
We report results here from three of the seven ques-
tionnaire forms. One included scaled measures of dis-
gust and contamination sensitivity. We used a shortened
8-item version of the disgust sensitivity scale (Haidt, Mc-
Cauley, & Rozin, 1994) to measure disgust sensitivity
(included in the Appendix). There is no generally ac-
cepted and validated contagion scale. Therefore, also on
the first questionnaire form, we used the Perceived Vul-
nerability to Disease scale to measure sensitivity to conta-
gion (Park, Faulkner, & Schaller, 2003). This scale in-
cludes two subscales: personal susceptibility to disease
(PVDSusc8) and attitudes/behaviors to interpersonal con-
tact (PVDAtt8) (the terminal “8” refers to the number of
items on each scale).
The second questionnaire included a range of transfor-
mations of raw sewage water. The items were included in a
single order for all subjects, beginning with what was sup-
posed to be generally acceptable versions of water (bottled
and tap) and raw sewage water, followed by a sequence of
more and more processed raw sewage water (see list of
items below). The instructions were:
Now we are going to ask you about your reac-
tion to a set of different kinds of water. In each
case, assume you are thirsty and that an eight-
ounce glass of the water described is available
for you to drink. Assume all the waters below
except raw sewage water and boiled sewage
water look and taste the SAME.
Rate on a scale of 0 to 10, how willing you are
to drink each type of water described (0 = to-
tally unwilling/uncomfortable; 10 = totally will-
ing/comfortable)
1. How willing are you to drink commercial
bottled water (from a spring)?
2. How willing are you to drink raw sewage
water?
3. How willing are you to drink commercial
bottled water (filtered tap water)?
4. How willing are you to drink tap water?
5. How willing are you to drink sewage water
that has been kept still so lighter things float to
the surface and heavier things sink to the bot-
tom, and then all these things are removed?
6. How willing are you to drink sewage water
that is filtered through soil to remove remaining
living microbes?
7. How willing are you to drink sewage water
that is passed through tightly meshed filters to
remove any microbes and unwanted chemicals?
8. The combination of the three treatments
above (in the order: 1. waste skimmed off bot-
tom and top, 2. filtered through soil, and 3.
passed through tightly meshed filters to remove
any remaining microbes and unwanted chemi-
cals) is called tertiary treatment. How willing
are you to drink sewage water that has been sub-
jected to tertiary treatment?
9. How willing are you to drink sewage water
that has been boiled enough to destroy all mi-
crobes?
10. How willing are you to drink sewage wa-
ter that has been boiled enough to destroy all
microbes, and then is evaporated, and then con-
densed and collected as pure water?
11. How willing are you to drink sewage water
subjected to tertiary treatment in an attractive
natural setting outside of town?
12. How willing are you to drink sewage wa-
ter subjected to tertiary treatment in an urban
water treatment plant?
13. How willing are you to drink 1 part sewage
water mixed with 1000 parts pure mountain
spring water?
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 54
14. How willing are you to drink 1 part ter-
tiary treated sewage water mixed with 1000
parts pure mountain spring water?
Question 14 was followed by:
15. If you scored less than 10 for willingness to
drink tertiary treated water (see question #8),
what could be done to the tertiary water so that
you would be as willing to drink it as you are the
bottled spring water?”
The third form of the questionnaire contained items on
the role of distance and time as moderators of strength of
recycled water aversion. One ordering of items was pre-
sented. Items and instructions were as follows:
Rate how comfortable (0 = not comfortable at
all to 10 = completely comfortable) you would
feel about drinking recycled water that has been
certified safe for drinking and then undergoes
the following additional treatments:
1. The water travels through a pipe directly
from the wastewater treatment plant to the pipes
that supply water to your city (no additional
treatment).
2. Leaving the water treatment plant, the water
travels one mile down a swift river.
3. Leaving the water treatment plant, the water
travels one hundred miles down a swift river.
4. Leaving the water treatment plant, the water
filters through an underground aquifer for 1
year.
5. Leaving the water treatment plant, the water
filters through an underground aquifer for 10
years.
6. Leaving the water treatment plant, the water
is deposited in a lake or reservoir for 1 year.
7. Leaving the water treatment plant, the water
is deposited in a lake or reservoir for 10 years.
This form also included a number of questions about
attitudes to recycled water. One of these is particularly
relevant to contamination issues, and we include it in the
set of results we describe here. The question was:
It is impossible for recycled water to be treated
to a high enough quality that I would want to use
it.”
The question was responded to with a standard five-
point agreement scale:
1 = disagree strongly, 2 = disagree, 3 = neither
agree nor disagree, 4 = agree, 5 = agree strongly
Table 1: Willingness to drink recycled water and suscepti-
bility to disgust and contagion.
Scale Unwilling Uncertain Willing ANOVA
DISG8 2.861 2.74 2.572 F(2,418) = 5.291∗∗
PVDSUSC8 3.41 3.24 3.14 F(2,429) = 1.381
PVDATT8 4.411 4.22 3.942 F(2,430) = 4.378∗∗
Note: Each scale has 8 items, so the maximum score is 8.
According to a Scheffé test, in any row, items labeled 1 are
significantly different than items labeled 2 at the p<.05 level.
∗∗ p<.01.
2.2 Results
Responses to the question “Would you be willing to drink
certified safe recycled water? (NO, UNCERTAIN, YES)”
were tabulated from 2,680 American subjects. There was
a surprising amount of acceptance of recycled water. Sum-
ming across all locations, only 12.9% said definitely no
(scored as zero) to willingness to try recycled water, while
38.0% said they would possibly try it (scored as one), and
almost half, 49.1% said they would definitely try it (scored
as two).
Disgust sensitivity and contagion sensitivity as mea-
sured by attitudes to interpersonal contact (PVDATT8)
significantly predict willingness to try recycled water, as
analyzed by ANOVA and post-hoc tests, displayed in Ta-
ble 1. In both cases, sensitivity declines significantly as
willingness increases. However, self-reported susceptibil-
ity to disease (PVDSusc8) did not significantly relate to
willingness to try recycled water. Results from the purifi-
cation sequences are displayed in Table 2, with the items
arranged in order of increasing comfort at drinking, on a 0-
10 scale. The range in comfort spanned from raw sewage
with a mean of .46 to bottled spring water at 9.15.
Skimming produces a slight (less than one point) but
significant (p<.01 by paired t-tests in this and all subse-
quent comparisons) improvement in comfort, and filter-
ing through soil another significant but small improve-
ment relative to skimming. Mesh filtering did not pro-
duce a significant improvement over soil filtering, and
the same is true for dilution of raw sewage 1:1000 with
spring water. Boiling, which would render the water safe
from micro-organisms but retain the sewage particulates
and color is slightly but significantly better than the prior
1:1000 dilution, but remains extremely uncomfortable (M
= 3.37). Even tertiary treatment (skim, soil filter, mesh fil-
ter) scores as quite unacceptable (M = 4.02), and it makes
no difference whether this is accomplished in an urban
or natural setting. Dilution of tertiary water 1:1000 with
spring water makes a significant but still small (less than
one point) increase in comfort (M = 4.82).
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 55
Table 2: Willingness to drink (0-10 Scale) various types
of water in order of increasing comfort.
Type of water N Mean S.D.
Raw sewage 419 0.46 1.715
Skim** 418 1.175 2.251
Soil filter** 417 1.969 2.72
Mesh filter 417 2.844 3.157
1:1000 Raw sewage 404 3.074 3.493
Boiled** 412 3.369 3.326
Tertiary urban 405 4.017 3.564
Tertiary 412 4.053 3.57
Tertiary nature 407 4.115 3.624
Tertiary 1:1000** 403 4.816 3.91
Boiled-evap-condensed** 410 5.044 3.779
Tap** 419 6.983 3.209
Bottle filtered tap** 419 8.422 2.616
Bottled spring** 419 9.148 2.121
Note: Significance of paired t-test between a
row and the row immediately above it. Paired
t-test because the unit is the difference be-
tween one rating and the one above it for each
subject.
** p<.01.
Surprisingly, boiling sewage water, evaporating it and
then condensing it, which produces a pure and safe water
that is at least as good as tap water, is rated at only 5.04,
significantly above diluted tertiary water, but still engen-
dering a great deal of discomfort. Tap water shows the
largest jump from its predecessor in the list, at 6.98 (1.84
units on the 10 point scale). This score is surprisingly low
considering the acceptability and use of tap water, and yet
it is higher than boiled/evaporated/condensed sewage wa-
ter, which in real-world terms (as opposed to psycholog-
ical terms) is more purified. Surprisingly again, bottled
filtered tap water scores much higher (M = 8.42) than tap
water, even though it is essentially the same thing! Bottled
spring water scores significantly and substantially higher
than bottled tap water (M = 9.15).
One insight from this series of questions is that there
is some understanding of the effects of the technological
sequence of water purification, in that willingness to con-
sume generally increased with incremental improvements
in water quality. (Note that the items were presented, after
the first few, in roughly the order of increased processing
or purity. This is a potential confound, but we tolerated it
because it made the questions much easier to process for
the respondents.)
Figure 1: Willingness to drink water as a function of pro-
cessing by initial willingness. Plus signs: willing to try
subjects; triangles: uncertain about trying, circles: unwill-
ing to try.
0 2 4 6 8 10
Mean willingness
Raw sewage
Skim
Soil filter
Mesh filter
Raw sewage
Boiled
Tertiary urban
Tertiary
Tertiary nature
Tertiary 1:1000
Boiled−evap−condensed
Tap
Bottled filtered tap
Bottled spring
Unwilling
Uncertain
Willing
There are also some striking findings in these results.
One is that boiled/evaporated/condensed water, which is
pure water, scores notably less (M = 5.03) than tap water
(M = 6.99; paired t(409)=9.399, p<.001; d’ = ,46). From
the point of view of purity, the former is better, but the
procedure is not used in water processing because it is
very expensive. The second surprise in the sequence is
that bottled filtered tap water scores notably higher (M =
8.42) than tap water (M= 6.98; paired t(417) = 10.569,
p<.001, d’ =.52 ). It is not clear whether the substantial
increase in comfort comes from the bottling or from the
filtering. If the latter, which would be the only rational
grounds for a preference, it is surprising how few people
put filters on their tap water faucets.
To explore individual differences, we repeated this anal-
ysis dividing subjects into those unwilling to sip recy-
cled water (n=43–45), uncertain whether they would sip
it (n=159–161), or definitely willing (n=206–211; Fig-
ure 1, Table 2). For all stages of purification, the water
is (not surprisingly) most acceptable to the willing and
least acceptable to the unwilling. The order of effective-
ness of the purification techniques is essentially the same
for the three groups. The groups are not significantly
different in discomfort for raw sewage water (F(2,415)
=2.026), the least acceptable form of water, and barely
differ for commercial bottled spring water, the most ac-
ceptable form ((F(2,414)=4.550, p=.011; unwilling M =
9.00, uncertain M = 8.79; willing M= 9.45; only signifi-
cant difference is between uncertain and willing, p=.012,
by Scheffé test). On the other hand, for the intermediate
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 56
states of purification, the group differences are large. For
boiled/evaporated condensed water, F(2,405) = 55.344,
with unwilling M = 1.26; uncertain M = 4.06; willing M =
6.57; all mean pairs differ at p<.001 by Scheffé tests. Sim-
ilarly, for tertiary treated water, F(2,402) = 69.090, with
unwilling M = 0.88; uncertain M = 2.71; willing M = 5.82;
all mean pairs differ at p<.001 by Scheffé tests, except
unwilling vs uncertain, p<.01 (Figure 1). The unwilling
group is essentially unaffected by all of the specific pu-
rification techniques described, never rising above a mean
rating of 1.6, until tap water, for which there is a very
large comfort jump to 5.31. In contrast, the willing sub-
jects showed a steady and substantial increase in comfort
with almost every more potent purification technique. Re-
sults from the uncertain group are intermediate. Like the
unwilling group, the uncertain group showed a very large
increase in comfort from boiled/ evaporated/condensed to
tap, as opposed to the more gradual increase in the willing
group.
2.2.1 Indelibility/spirituality of contagion
The results of the “titration” of purification, reported
above, suggest that, for a minority of individuals, wa-
ter contamination is indelible, and essentially behaves as
spiritual contagion. On the third version of the question-
naire, we included a question that assessed this directly:
“It is impossible for recycled water to be treated to a high
enough quality that I would want to use it.”
Overall, 26% of 380 subjects who received the third
questionnaire version agreed (scoring 4 or 5) with this
statement. Breaking this down by our standard, first page
question on the acceptability of recycled water, 48% (of
44 individuals) who were unwilling to try it, 28% (of 163)
individuals who were uncertain about trying it, and 19%
(of 174) who were willing to try it endorsed indelibility
of contamination in wastewater. There is, of course, some
contradiction for the latter 19% between claiming they are
willing to try recycled water and reporting that there is
no treatment of recycled water that would make it accept-
able. An ANOVA on willingness by group based on scores
from the 5 point scale was highly significant, F(2,378) =
22.492, p<.001). Individuals uncertain about willingness
to try recycled water opted for indelibility significantly
more than those willing (Scheffé test p<.01).
A total of 412 people answered the question about com-
fort with drinking tertiary processed water. Of these, only
48 were totally comfortable (10) with tertiary processed
water. Of the 364 eligible to answer the open-ended ques-
tion about whether anything could be done to this water to
make it reach “10”, 209 individuals gave categorizable an-
swers to this question. We categorized answers as (in order
of decreasing response number): more treatment needed
(sometimes specific treatments were proposed; 27% of
responses); nothing (meaning nothing could be done to
make the water totally comfortable [10 rating] to drink;
24%); more information needed (usually as to the status
of the water; 23%), less information needed (meaning that
the subject did not want to hear about the processing his-
tory of the water; 15%), and unsure (10%). The unwill-
ing group (n=25), as might be expected, showed by far
the highest incidence of “nothing could be done” (76% of
all reasons offered by that group). The uncertain group
(n=78) had “nothing” also as the highest incidence reason,
but it was only for 31% of subjects. For the willing group
(n=106), the most common reason was further treatment
(35% of cases).
2.2.2 Distance and time
By the magical contagion principle of permanence, re-
luctance to drink recycled water should not be reduced
much by either increasing the time or distance between
completion of water processing and the opportunity to
drink the water. Water treatment in the U.S. occurs in the
factory-like settings of treatment plants. Water is then re-
leased into, or stored in, managed “natural” systems such
as flow-regulated rivers, aquifers, or reservoirs. Time in
storage and distance traveled are both potential decontam-
inants. Of course, it is the long time and distance between
wastewater and tap water required by the hydrological cy-
cle that functions, one way or another, to make tap wa-
ter acceptable. In fact, however, in some cases treated
wastewater introduced into natural storage or carriage sys-
tems is of a higher quality than the receiving waters.
Rather than serving as a physical purification, the
reintroduction of treated wastewater into natural systems
could potentially serve a “spiritually purifying” role of
removing consumers’ historical association of the clean
water with its origins as wastewater, in much the same
way that contact with Mother Theresa can render one
of Hitler’s jackets acceptable. Time and distance as de-
scribed here do not necessarily improve water quality
and might reduce it in real-world terms. However, the
mixing of treated wastewater with “natural” water (even
though the natural water itself was once wastewater), and
the interaction with large natural bodies of fresh water
might serve to negate the wastewater history by counter-
acting it with positively-valenced “naturalness” (Nemeroff
& Rozin, 1994). Of course, it is also possible that this
same interaction would contaminate the “natural” water.
The questions on time and distance were presented in
sequence so subjects could directly compare effects of one
versus one hundred miles, or time intervals of one versus
ten years, in terms of their efficacy in rendering the wa-
ter acceptable. Such within-subject comparisons should
optimize the detection of small differences.
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 57
Table 3: Change in comfort drinking water that had been in a reservoir or aquifer for one versus 10 years, by willingness
to accept recycled water (N/Mean/(SD)).
Amount improved in all
subjects
Amount improvement in Ss
who start at <10 at one year
Percent of subjects <10 at
start showing improvement
Aquifer Reservoir Aquifer Reservoir Aquifer Reservoir
Willing 187 186 138 156 47% 29%
0.48** 0.20 0.74*** 0.24
(2.02) (2.07) (2.12) (2.56)
Uncertain 165 165 145 159 50% 27%
0.78*** 0.49** 0.93*** 0.51**
(2.10) (2.08) (2.16) (2.12)
Unwilling 44 44 39 39 41% 22%
0.39 −0.02 0.69 0.22
(2.54) (2.15) (2.08) (1.58)
Note: ** p<.01, *** p<.001. Significance level refers to significantly different from 0 by 2-tailed t-test.
Overall, 39% of respondents showed an increased will-
ingness to drink water after it had been in an aquifer for
ten years versus one year, as opposed to 14% who found
ten years less acceptable than one year. Comparable val-
ues for the reservoir are 25% and 17%, respectively. There
is a significant increase in comfort for the aquifer with the
nine years of extra time generating higher mean comfort
(Mdiff = 0.59, SD = 2.11, t(397) = 5.581, p<.001). There
is a comparable but smaller significant enhancement from
10 years in the reservoir (Mdiff = 0.30, SD = 2.08, t(396) =
2.819, p<.01).
The means for willingness to drink recycled water are
presented in Table 3. A direct comparison of these means
is not warranted, because many of the 187 willing re-
spondents already have a maximum 10 comfort score for
drinking certified safe water before storage. Also, the in-
creased value of nine extra years of storage cannot be eas-
ily gauged across the three willingness groups, since the
groups start at different comfort levels. Nonetheless, ex-
amination of Table 3 suggests that time in aquifer is more
effective than time in reservoir (Mdiff = .32, t(394) = 2.473,
p<.05). Our subsequent analyses do not include subjects
who were already at the maximum (10) acceptability level.
Overall, 39.7% of respondents showed an increased
willingness to drink water after it had traveled for a hun-
dred miles versus one mile. However, the mean advantage
of the extra 99 miles for all respondents was slight; elim-
inating all respondents who were at the maximum com-
fort (10) at mile one, the mean difference is .40 units (SD
= 2.30) on the 0-10 scale (t(369) = 3.353, p <.001). As
shown in Table 4, there are not major differences across
initial willingness groups, with about 30% in each group
showing some increase in acceptability after 99 additional
miles of travel down a swift river.
2.3 Discussion
In terms of the taxonomy of contagion described by Ne-
meroff and Rozin (1994), the unwilling respondents and
some of the uncertain respondents appear to treat the ef-
fect of water coming into contact with sewage as showing
indelible, or “spiritual” contamination. This means that
further processing or more details about processing may
be an ineffective strategy for increasing acceptance. The
fact that tap water is much more acceptable than water
that is actually safer (boiled/evaporated/condensed) sug-
gests that tap water acceptability is based in part on either
ignorance of the purification process, or failure to think
about it at the point of drinking it. The lower discomfort
for tap water might also result from its familiarity, which
could dampen concerns about risk (Slovic, Fischhoff &
Lichtenstein, 1980).
The relation between willingness to sip a water sam-
ple and disgust sensitivity is subject to multiple interpre-
tations. Most of the transformations of water that were
described would have the same clear appearance, so there
would be no visual cue (such as brownness) that might
directly elicit disgust. But disgust sensitivity includes sen-
sitivity to contamination, and that varies markedly across
the different water exemplars.
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 58
Table 4: Effect of distance traveled down a swift river
on acceptability of water by willingness to drink recycled
water (hundred miles minus one mile: comfortable 0-10)
(n/mean/(SD)).
Amount
improved in all
subjects1
Amount
improved in S
<10 at one
mile1,2
Percent of
subjects <10 at
mile one showing
improvement
Willing
188 168 32%
0.06 0.22
(2.51) (2.47)
Uncertain
162 146 27%
0.38* 0.48**
(2.29) (2.13)
Unwilling
44 0.43 30%
0.80 0.81
(2.18) (2.21)
1 mean improvement (comfort at 100 miles minus
comfort at 1 mile).
2 Only includes subjects with a possibility for
improvement, i.e., one mile comfort < 10.
* p<.05, ** p<.01.
3 Study 2: Reactions to recycled wa-
ter and its relation to disgust and
contagion sensitivity: A study with
college students
A major limitation of Study 1 is that the best practical
treatment for making water acceptable and safe for drink-
ing, reverse osmosis (RO), was not clearly articulated as an
option. Reverse osmosis involves forcing water through a
membrane filter system which passes only molecules the
size of water or smaller, essentially generating pure wa-
ter. This technique has become the procedure of choice
in most of the world, including the U.S., for generating
potable water from wastewater or other highly-degraded
source water. In the larger study, the item “. . . passed
through tightly meshed filters to remove any microbes and
unwanted chemicals” was originally intended as a descrip-
tion in lay terms of reverse osmosis. However it was
overly vague and not clearly labeled as RO. This was cor-
rected in Study 2. Carried out after Study 1, Study 2 fo-
cuses on the acceptability of (comfort with) “purified” wa-
ter. The subjects were American college students. The
survey was considerably longer than the prior survey, and
allowed for the completion of a full disgust scale, a scale
to measure obsessive-compulsive tendencies (which might
relate to the contamination sensitivity that seems so cen-
tral to water acceptance), and a new measure of contam-
ination sensitivity devised for this study, which measures
reactions to purification of water contaminated with dif-
ferent types of entities. We also looked at acceptability of
tap water and consumption of bottled water as predictors
of willingness to drink recycled water.
3.1 Methods
Subjects were 432 University of Pennsylvania undergrad-
uates from an introductory psychology course (61.3% fe-
male). The question which introduced the section on water
attitudes for this study, was:
For the following items, please use the scale be-
low to indicate how uncomfortable you would
feel taking a sip of the water described. The
scale runs from 0= completely comfortable
(e.g., the same as how you would feel about tak-
ing a sip of water from a previously sealed com-
mercial bottle of spring water {e.g., Evian, Fuji,
Poland Springs}) to 100 = as uncomfortable as
any activity you have experienced.
Your level of discomfort about taking a sip of
water from a previously sealed commercial bot-
tle of spring water (e.g., Evian, Fuji, Poland
Springs): PLEASE ENTER A ZERO (0) FOR
THIS ITEM FOR PURPOSES OF CALIBRA-
TION.
Local tap water
Wastewater that is boiled and evaporated into
water vapor, and then condensed.
Wastewater that is forced through a filter that has
holes so small that nothing bigger than a water
molecule can get through (this is called ultrafil-
tration or reverse osmosis).
(There is an inaccuracy in the last item. Ultrafiltration and
reverse osmosis are in fact not equivalent; ultrafiltration is
not as thorough in removing contaminants as reverse os-
mosis and used alone will not yield potable water. How-
ever, the procedure we describe is, in fact, reverse osmo-
sis, and this is the core of the question. We doubt that more
than a few if any of our subjects knew what either the term
“reverse osmosis” or “ultrafiltration” meant.)
A set of similar items was included focusing on removal
of different types of contamination from water, using the
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 59
same scale. Previous work on magical contagion (e.g.,
Rozin et al., 1986; Nemeroff & Rozin, 1994; reviewed
in Rozin & Nemeroff, 2002) exploring mental models
of contagion and the “moral-germ conflation” compared
(actually harmless) exposures to different types of conta-
gious sources, representing danger, disgust, moral taint,
and physical illness. The four contaminants included in
Study 2, all added to bottled spring water, were: “a tiny
(harmless) amount of sodium cyanide” (danger), “brief ex-
posure to a heat sterilized cockroach: (disgust)”, “sipped
by a convicted murderer” (moral taint), and “exposure to
active HIV viruses” (physical illness). For three of the four
contaminants, respondents rated their reaction to the con-
taminated water. Then, in the decontamination sequence,
the contaminated water “is poured out, and the glass is
thoroughly washed with soap and water, and then rinsed
with more bottled water. The glass is then heat sterilized.
Now more bottled water is poured in. [rate] Your discom-
fort at taking a sip of this water.”
For sodium cyanide, the description was as follows:
Imagine taking a sip of water poured into a clean
new glass from another freshly opened bottle
of the same water as above (e.g., Evian, Fuji,
Poland Springs) after a tiny amount (.01 gram)
of the poison sodium cyanide has been mixed in.
This dose of sodium cyanide has no effect at all,
and is no more than you would find in an apri-
cot pit. Sodium cyanide is NOT a cumulative
poison. At this dose it will have absolutely no
effect.
[rate] Your discomfort at taking a sip of this wa-
ter
After the decontamination sequence described above,
respondents again rated their discomfort at sipping the wa-
ter.
For cockroach, the description was identical except that
the cyanide description was replaced with “A heat steril-
ized dead cockroach is briefly dipped into the new glass of
water.” For murderer, “A convicted murderer takes a sip
from the new glass of water.”
For HIV/AIDS the situation was different, because a
trace of virus is actually physically dangerous. “A drop
containing active HIV (AIDS) viruses is dropped into a
new glass of water. The water is then heat sterilized at
400 degrees Centigrade for one hour, which will kill any
known organism many times over. The glass cools down
to drinking temperature.” After a discomfort rating for
this sterilized water, the same decontamination sequence
as above was carried out, followed by another discomfort
rating.
As a measure of contagion sensitivity, we averaged the
discomfort scores after decontamination for each of the
four contaminants. This is a measure of residual, roughly
Table 5: Comfort at sipping three different types of water
(n=403 undergraduates).
Water type
Mean
discomfort
Standard
deviation
Percent
totally
comfort-
able
(0)
Percent
totally
uncomfort-
able
(100)
Tap 19.38 24.69 27.5% 1.2%
Boil/
evaporate/
condense
40.28 32.97 12.7% 6.5%
Filtered:
reverse
osmosis
36.38 33.50 17.4% 5.5%
spiritual contamination across the four contaminants. The
mean discomfort scores were 9.0 for cyanide, 26.9 for
cockroach, 16.5 for murderer, and 47.2 for AIDS. The in-
tercorrelations of the four contamination scores with one
another varied between .28 and .55.
Subjects were also asked:
In a typical week, how much of bottled versus
tap water do you drink?
% bottled __
% tap __
Later in the questionnaire, subjects took the Disgust
Scale (Haidt, McCauley & Rozin, 1994), as modified and
shortened (from 32 to 27 items by Olatunji et al., 2007).
Finally, subjects completed the 18-item Obsessive-
Compulsive Inventory (Foa et al., 2002).
3.2 Results
All subjects (N=401–410 of 432) included in the analy-
sis rated discomfort at drinking commercial bottled water
at “0”, as instructed. There is a major reduction in dis-
comfort (from the presumed 100 baseline) from either of
the purification techniques (reverse osmosis, M=36.4; or
evaporation/condensation, M =40.3). However, the level
of discomfort from either is still much higher (p<.001)
than the discomfort from tap water (M=19.4; see Table
5). Discomfort was significantly higher for the evapo-
rated/condensed than the reverse osmosis water (t(393) =
4.329, p<.001). A small number of subjects (6%) showed
maximal discomfort after either of the processes, while
13% were totally comfortable (0) after evaporation/ con-
densation and 17% after reverse osmosis. Although re-
verse osmosis was on average more effective than evapo-
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 60
ration/condensation, for 16% of subjects, evaporation was
more effective by more than 5 points.
What predicts the reduction in discomfort resulting
from reverse osmosis purification? (Since reverse osmo-
sis and evaporation/condensation reductions decontami-
nated scores correlate .77, we consider only the first pu-
rification technique.) The best predictors were, in de-
creasing order: the mean of the four contagion scores
after washing/sterilization (r = .52, p<.001), discomfort
with sipping tap water (r = .42, p <.001), the disgust
scale score (r = .41, p<.001), percent of total water in-
take consumed as bottled water (r = .21, p<.001), and fi-
nally, obsessive-compulsive tendency score (r = .09, n.s.).
A straight (unique variation accounted for) linear regres-
sion identified the contagion mean as the principal predic-
tor (beta =.36, p<.001), with tap water discomfort as the
next predictor (beta=.24, p<.001) and then disgust sensi-
tivity (beta=.20, p<.001). Obsessive-compulsive tenden-
cies and percent of water consumed as bottled water had
no significant unique predictive value.
4 General discussion
We report two very different studies, one with a short sur-
vey administered to a broad sample of Americans, and the
other with a more intensive survey completed by Ameri-
can undergraduates. Both focus on individual differences
in disgust and contagion, in relation to the acceptability
of contaminated water, and specific responses to decon-
taminated wastewater. The studies have convergent con-
clusions: there is wide variation in the reported accept-
ability of recycled water; there is wide variation in disgust
and contamination sensitivity; there is a substantial rela-
tion between disgust and/or contamination sensitivity and
acceptability of processed and safe but recently contam-
inated water; there is a minority of individuals who will
not accept previously contaminated water no matter what
purifications it undergoes. This is particularly striking, be-
cause these same people readily consume tap or bottled
spring water, which usually have the very same contam-
ination history as the water that they reject as contami-
nated. We can describe these individuals as responding to
what we call spiritual contamination. When we describe
levels of processing (purification) which produce water
that is purer than tap or bottled water, subjects still rate
this water as less acceptable than tap water.
In addition, each study has study-specific implications.
The first, large study reveals that those uncertain about
drinking recycled water show some positive effects of in-
creasing amounts of processing: these effects are much
larger than the virtually zero effects shown by those un-
willing to drink recycled water, but are notably less than
those willing to drink it. In addition, with respect to the
magical contagion principle of dose insensitivity, allow-
ing considerable time to pass after recycling (10 years)
with water stored in a reservoir or aquifer, or having the
recycled water travel a long distance (100 miles) in a swift
river produces only a small (but significant) increase in ac-
ceptability (comfort).
The undergraduate results indicate that obsessive-
compulsive tendencies are not substantially related to wa-
ter rejection. This may be because the standard OCD
scale focusses on the degree to which individuals are
bothered by their obsessions, rather than directly on sen-
sitivity. Reverse osmosis, the currently preferred tech-
nique to produce potable water, is somewhat more effec-
tive than boiling/evaporation/condensation for producing
acceptable water.
It is clear that some opponents of recycled water are
essentially opposed to it in principle—it is like a moral
stance. This is reminiscent of a minority of supporters
of naturalness, for whom natural preference is ideational,
and not subject to counter-evidence (Rozin et al., 2004).
Similarly, there is a theme of moral opposition to genet-
ically modified organisms which is evidence-insensitive
(Scholderer & Frewer, 2003; Frewer et al., 2013; Scott,
Inbar & Rozin, 2015). “Natural” has some of the prop-
erties of a protected or sacred value (Baron & Spranca,
1997; Tetlock, 2003). One of these is evidence insensitiv-
ity. This type of opposition is very difficult to influence.
Our results indicate that intuitive contagion-based
thinking is involved in public reactions to recycled wa-
ter. Our findings are consistent with those of Callaghan et
al.’s (2012) qualitative study, which identified the theme
of purity/impurity as a component of their Australian sub-
jects’ responses to water recycling. These authors noted
that while subjects were aware of the need to use recycled
water, they nevertheless exhibited a fear of contamination
from it.
Understanding the intuitive psychology of contagion
allows us to identify circumstances and ways in which
intuitive, heuristic-based thinking can clash with ex-
pert/scientific models, leading to suboptimal choices and
behaviors. The findings we report generate suggestions
about ways to bring public responses into better alignment
with real-world contingencies, by identifying the magical
law of contagion as a cognitive heuristic, which functions,
among other things, to limit damage due to infectious
agents. Such cognitive shortcuts are not perfect, how-
ever, and in the case of recycled water, the impact may
be counter to the public interest.
Just as contact with Mother Theresa can cancel out the
Hitlerness in a jacket (Nemeroff & Rozin, 1994), the ad-
dition of the right positive elements (additional processes
described as “natural”, images of “ultra-purity”) may undo
contamination for those people whose thinking follows a
spiritual model.
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 61
In connection with this, it is interesting to note that a
study by U.S. water-reuse experts comments on the impor-
tance of “environmental buffers” (lakes, rivers, aquifers)
to water supply: “Environmental buffers can play an im-
portant role in improving water quality and ensuring pub-
lic acceptance of potable water reuse projects. . . but the
historical distinction between direct and indirect water
reuse is not meaningful to the assessment of the quality
of water delivered to consumers.” (NRC, 2012, p. 54).
“Indirect” water reuse means the water is released to a
natural system before being recaptured for subsequent use.
“Direct” means the water has bypassed natural systems
and is being directly reintroduced into flows intended for
human uses. This finding, written in bold face in the study,
suggests that either there is no benefit from the reintroduc-
tion of water to a natural system, or that technologies used
to treat wastewater prior to personal uses are so effective
and reliable that natural systems are no longer needed. In
fact, reintroducing water into the natural system actually
adds impurities back into the recycled water. However, the
authors point out a “public acceptance” benefit from intro-
ducing treated wastewater into natural systems before its
next use.
Other approaches focus more on the ecological, health
and economic advantages of recycled water. For exam-
ple, one could create a context where recycled water is
so commonly and widely discussed as to become familiar
rather than novel. The simple shift from novelty to every-
day familiarity can decrease perceived threat (Slovic et al.,
1980). The more recycled water becomes a norm, the less
problematic it will be (e.g., Zajonc, 2001). The marketing
of recycled water (NeWater), by Singapore, is an example.
Yet another approach invokes framing: developing wa-
ter treatment and delivery methods, and ways of commu-
nicating about the water, that frame the water’s history as
sewage out of awareness. This naturally occurs when wa-
ter comes out of a tap, or better yet, a discrete unit such as
a bottle. As noted earlier, recent research on acceptance
of recycled water focuses on whether the words used to
describe the water matter to acceptance (Menegaki et al.,
2009), whether knowledge of treatment processes matter
(Dolnicar et al., 2010), and what impact the level of trust in
the purveyor of the water has (Doria, 2010). Many of these
findings (though not all) can be understood in terms of
framing the water’s history as sewage out of focal aware-
ness. A framing approach risks failing when and if oppo-
nents act to bring the framed-out material back into focus
(e.g.,“toilet to tap” campaigns). However if the frame ac-
tivates cognitive structures related to perceptions of safety
(e.g., plastic wrapping around meat in a grocery store) they
may withstand such efforts.
Borrowing from the phobia treatment technique of sys-
tematic desensitization, one could introduce recycled wa-
ter in very low concentrations into the water system, and
gradually increase the levels. Our data for the unwilling
subjects in the present study suggest that this technique
will have a limited effect with them, but it may have been
effective in Singapore. Borrowing again from phobia and
related treatments, the opposite of systematic desensiti-
zation is flooding. For the case of recycled water, this
consists of convincing people that all water is contami-
nated, and all essentially “toilet to tap.” This could poten-
tially lead to some personal crises, but the desire to survive
would presumably dominate.
Arguably, from a public health perspective, the sim-
plest solution to the acceptability problem of otherwise
safe, potable water is to gradually increase the amount of
potable, recycled water in the water supply without telling
anyone, because in general people tend to underestimate
the extent to which they will adapt to things. By the time
this is discovered, people would presumably realize that
it has been OK to drink this water. Obviously, though,
this would engender the nontrivial problem of loss of trust,
and raise substantial ethical issues. As we note in the in-
troduction, in a truly democratic society a highly engaged
and affluent, but rather small minority can often impede
progress that would increase the public good. It is for this
reason that we must attend to the thinking of the minority
who are strongly opposed to water recycling. Telling them
just that they will get used to it, as people got used to water
fluoridation, will not be convincing, although it is true.
Alternatively, one could wait until local water shortages
are so severe that inconvenience and cost drive people to
accept what they previously found unacceptable. We have
survey data that suggests that, although people acknowl-
edge magical contagion beliefs, they may abandon them
when there is an economic cost to having these beliefs
drive their behavior (Rozin et al., 2007). Economic forces
can operate directly as incentives, or they can highlight for
people their own irrationality. Singapore has dealt most
effectively with the introduction of recycled water. Liti-
gious minorities are ineffective there. The government has
established a clean and effective recycled water facility,
and conducts tours of it regularly. Recycled bottled water
(NeWater) is provided free at any event that requests it.
The recycled water is not introduced directly into drinking
water, but is rather randomly introduced into holding tanks
and reservoirs. A great deal of government-sponsored per-
suasive information is presented to the public. Singapore
does not want to be dependent on other countries for water,
and this provides a political/economic motivation.
There is an alternative for a committed small minority.
Individuals who are very strongly opposed to consuming
recycled water can buy bottled spring water, and avoid the
problem of direct consumption. There are historical ex-
amples of people avoiding public water supplies, as with
the case of fluoridation.
Judgment and Decision Making, Vol. 10, No. 1, January 2015 Rejection of recycled water 62
Resistance to recycled water is largely psychological.
There are many examples where people’s feelings or intu-
itions run counter to their own rationally considered self-
interest (Slovic, Finucane, Peters, &MacGregor, 2004; re-
viewed in Baron, 2008; Kahneman, 2011), and sometimes
the public interest. Strategies for dealing with this mis-
match need further attention.
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Appendix: Short disgust scale
Please indicate how much you agree with each of the fol-
lowing statements, or how true it is about you. Please write
a number (1, 2, 3 or 4) to indicate your answer:
1 = Strongly disagree (very untrue about me) 2 = Mildly
disagree (somewhat untrue about me) 3 = Mildly agree
(somewhat true about me) 4 = Strongly agree (very true
about me)
I try to avoid letting any part of my body touch the toilet
seat in a public restroom, even when it appears clean.
It would make me uncomfortable to hear a couple mak-
ing love in the next room of a hotel.
It would bother me tremendously to touch a dead body.
Even if I was hungry, I would not drink a bowl of
my favorite soup if it had been stirred by a used but
thoroughly washed fly-swatter.
How disgusting would you find each of the following
experiences? Please write a number (1, 2, 3, or 4) to indi-
cate your answer:
1 = Not disgusting at all, 2 = Slightly disgusting, 3 = Mod-
erately disgusting, 4 = Very disgusting (If you think some-
thing is bad or unpleasant, but not disgusting, you should
write "1".)
You take a sip of soda and then realize that you picked
up the wrong can, which a stranger had been drinking out
of.
You hear about a 30 year old man who seeks sexual
relationships with 80 year old women.
While you are walking through a tunnel under a railroad
track, you smell urine.
You accidentally touch the ashes of a person who has
been cremated.