Known Unknowns: Knowledge, Confidence, and Public Opinion on Water Reuse

Public acceptance can constrain treated-wastewater reuse, but less is known about whether citizens provide a substantive view at all. An influential account of opposition to contested technologies predicts that the strongest opponents know the least while believing they know the most. We test that joint prediction using a knowledge–attitudes–practices survey of 1,069 households in Barbados. The survey separately measures demonstrated topic knowledge, self-assessed knowledge, willingness to use reclaimed water, and explicit 'don’t know' responses. Among respondents who provide a complete willingness profile, demonstrated knowledge is essentially unrelated to acceptance, whereas self-assessed knowledge is positively associated with acceptance. The predicted knowledge-overconfidence configuration therefore does not appear in this setting. The strongest knowledge gradient instead lies on the response margin: a one-standard-deviation increase in demonstrated knowledge is associated with a 5.8-percentage-point lower probability of giving at least one 'don’t know' response, against a base rate of 22.6 per cent. The relationship reappears in three sectoral attitude batteries and attenuates by about 19 per cent after controlling for out-of-module nonresponse. The evidence therefore points away from confidently mistaken opposition and toward a sizeable group that is less knowledgeable and more likely to express uncertainty.