*3.4. Comparing Groups*

The six clusters—*bottled only, tap only, appliance filter only, bottled & tap, sink filter & mixed*, and *mixed except sink*—differed not only in their water source choice patterns but also in terms of trust, salience, risk, and tap water evaluation variables (see Figure 4 for a comparison of differences significant at a *p* < 0.05 level; Table S2 contains full ANOVA results; Table S3 contains full pairwise comparison results).

**Figure 4.** Post hoc pairwise comparisons of adjusted linear predictions of mean differences (first cluster–second cluster) between clusters for each predictor variable. Predictions were calculated using a Bonferroni test with 95% confidence intervals. Only significant differences at a *p* < 0.05 level are displayed.

Clusters were most similar in terms of affect risk perceptions (Figure 4C: affect safety and Figure 4E: affect severity) and salience variables (Figure 4G: attention and information known), evidenced by the lower number of mean differences between pairs in those variables. In contrast, comparative risk perceptions (Figure 4F) and organoleptic evaluations (Figure 4H) were most effective at distinguishing between groups.

3.4.1. H1: Those with Higher Trust in Their Water Utility to Provide Safe Drinking Water to Them Will Be More Likely to Drink Their Tap Water in Their Homes as Opposed to Drinking from Other Sources

The results of the pairwise comparisons mostly support our hypothesis that higher trust is related to the increased choice of tap water. Residents in the *tap only* cluster trusted their utility to deliver safe drinking water to them more than those in all other clusters except *bottled & tap* (Figure 4A; Table S3). Exclusive *tap water* drinkers' trust was much higher (mean (m) = 7.60) than that of exclusive *bottled water* drinkers (m = 5.26) (Cohen's d = 1.32)

or *sink filter & mixed* water source drinkers (m = 5.75; Cohen's d = 1.23), moderately higher than that of *mixed except for sink filter* drinkers (m = 6.25; Cohen's d = 0.91), and slightly higher than that of *appliance filter* drinkers (m = 6.45; Cohen's d = 0.70).

3.4.2. H2: Those with Greater Risk Perceptions Associated with Their Tap Water Will Be Less Likely to Drink Their Tap Water in Their Home as Opposed to Drinking from Other Sources

We found partial support for this hypothesis. Clusters with tap water central to their drinking water choices had lower risk perceptions than some other behavioral clusters, but not all of them. Residents who drank *tap water* exclusively believed more strongly that their tap water was safe to drink (m = 1.21) than exclusive *bottled water* drinkers (m = 2.18; Cohen's d = −1.19) or *sink filter & mixed* water drinkers (m = 2.08; Cohen's d = −1.31) did (Figure 4B; Table S3). Exclusive tap water drinkers were on average *not* concerned about the safety of their tap water (m = 1.43). While they were less concerned than *bottled only* drinkers (m = 2.30; Cohen's d = −0.79), they did not differ in concern level from other behavioral groups (Figure 4C).

Residents who drank *tap* water exclusively reported that they would be more worried or angry if they lost access to drinking water (m = 3.38) than exclusive *bottled* water drinkers (m = 2.58; Cohen's d = 0.66; Figure 4E). Residents who drank *tap* water exclusively were also much more likely to think that not having access to their home tap water would directly impact their lives (m = 3.94) than people who drank *bottled water only* (m = 2.22; Cohen's d = 1.40) and moderately more likely than those who drank both *bottled & tap* water (m = 3.13; Cohen's d = 0.66; Figure 4D).

The comparative risk variable, asking about the relative safety of tap water compared to bottled water, differentiated tap water drinkers from almost every other cluster (Figure 4F). Residents who drank *tap water* exclusively believed that tap water is no different from bottled water in terms of safety (m = 2.88). Those who drank *bottled water* exclusively believed much more strongly that bottled water is safer than tap (m = 4.28; Cohen's d = −1.78). Most other groups also believed that bottled water is safer than tap, including those who drank *bottled & tap* water (m = 3.64; Cohen's d = −0.92), *sink filter & mixed* water sources (m = 3.52; Cohen's d = −0.71), and from *mixed water sources excepting a sink filter* (m = 3.58; Cohen's d = −0.80). There was no difference between the *tap water only* cluster and the *appliance filter only* cluster in terms of their beliefs about bottled versus tap water safety.

Overall, cognitive and comparative risk perceptions (Figure 4F) differed more than affective risk perceptions (Figure 4C,E) between clusters, as demonstrated by the larger effect sizes between means. Exclusive *tap water* drinkers had lower risk perceptions than several non-tap water clusters, but it was not universal. Exclusive *bottled water* drinkers and exclusive *tap water* drinkers differed across all variables, unlike other pairs of clusters, and had stronger effect size differences than with other groups. Exclusive tap water and appliance filter clusters did not show different means across any of the risk indicators.

3.4.3. H3: Issue Salience Is Related to In-Home Drinking Water Choice. Specifically


The pairwise comparison results did not support our first salience hypothesis (H3a), as information known about water quality was similar across the six clusters (*F* (5, 298) = 1.85, *p* = 0.103). The results partially support the hypothesis that attention paid to tap water quality is related to lower use of tap water (H3b; Figure 4G). Exclusive *tap water* drinkers noticed changes in their tap water (m = 1.31) less frequently than exclusive *bottled water* drinkers (m = 1.92; Cohen's d = −0.95), *sink filter & mixed* water source drinkers (m = 1.98; Cohen's d = −1.05), and *mixed water source excepting sink filter* drinkers (m = 1.75; Cohen's d = −0.75). The *appliance filter only* cluster and *bottled & tap* cluster did not differ from the *tap only* cluster.

3.4.4. H4: Those with more Positive Organoleptic Water Quality Evaluations Will Be More Likely to Drink from Tap Water Sources in Their Home

Exclusive *tap water* drinkers had more favorable perceptions of their tap water quality (m = 4.35) than every other behavioral cluster (Figure 4H), supporting our fourth hypothesis. This difference was particularly pronounced with exclusive *bottled water* drinkers (m = 3.01; Cohen's d = 1.77) and *sink & mixed water source* drinkers (m = 3.28; Cohen's d = 1.48), and least pronounced with *appliance filter* drinkers, although still with a moderate effect difference (m = 3.91; Cohen's d = 0.62).

Overall, the ANOVA results (Figure 4 for selected comparison; Table S2 for full results) generally supported the hypotheses that tap water drinkers would have lower risk perceptions, higher trust, and higher water quality perceptions than other clusters. Exclusive tap water drinkers had the lowest number of differences with exclusive appliance water drinkers, suggesting a similarity between those clusters. Exclusive tap water drinkers showed the strongest differences when compared to exclusive bottled water drinkers and sink and mixed water source drinkers. This was evidenced by the high mean differences and effect sizes between those clusters compared to other pairs and the consistency with which those groups differed between variables.
