be mitigation strategies available (e.g., the possibility of switching to a nearby safer well). All these conditions were present in the empirical context of this study.

The first condition is satisfied by the large majority of respondents (76%) who did not know whether their well water was safe or unsafe to drink (Table 1). In addition, very few wells had visible signs of safety status such as paint, so even households with strong priors about the safety of their well water may have valued the possibility to demonstrate water quality to others by displaying test results.<sup>14</sup> That the tests could provide new information also required trust, as there is growing evidence that lack of trust in health-related information may hinder the adoption of behavior that could reduce health risks (Cohen et al. 2015, Bennett et al. 2017, Alsan and Wanamaker 2017, Martinez-Bravo and Stegmann 2019). Although the data do not include measures of trust, water tests were not a novelty because many wells had been tested in the past in Sonargaon. In addition, earlier work carried out in the neighboring Araihazar sub-district found switching rates from unsafe to safe wells after testing of between one-third and three-quarters (see Section 1 for references), consistent with a high degree of trust in the results.

The second condition (relevance of the information) is also satisfied because virtually all respondents knew in a general sense about the presence and health risks of arsenic in tube well water. Data on risk perceptions collected in neighboring Araihazar in 2008 indicated that a majority of respondents were aware not only of the serious nature of arsenic risk, but also that the risk becomes more severe with prolonged exposure, see Tarozzi (2016, Figure 4) for details.

Finally, the third condition (perceived availability of alternative sources of drinking water) was also likely satisfied given that well-sharing was already practiced in the area (see Section 3). To some extent households were therefore already aware of the possibility of using neighbours’ well water for drinking. Data from neighboring Araihazar show that the BAMWSP testing campaign conducted about 10 years earlier led to a substantial degree of well sharing (Balasubramanya et al. 2014). On the one hand, the figures in Table 1 show that about three quarter of wells had been found to be unsafe by BAMWSP in the study area, and this may have reduced the perceived chance to have safe options nearby in case of bad news. On the other hand, the average household had more than 10 other wells within a short 50 m radius and about 30 within 100 m, and such dense network of wells likely increased the perceived likelihood of having safe wells close by.

Overall, differences in switching rates between any two experimental arms could have emerged either from different selection into purchase or from the way information was provided (in which case even identical buyers may have reacted differently). The decision to change source was still likely to depend primarily on any new information made available by the test results. Hence, regardless of the

> 14In principle, such value needs not be positive, for instance if knowledge of a high-arsenic well is perceived as lowering land value, or signaling poor health among household members, or is more generally stigmatized. In Bihar, India, Barnwal et al. (2017) find that placards indicating unsafe arsenic levels were more likely to be removed by households than those indicating low levels of arsenic two years after installation, although such behavior may have also been justified by the desire not to be reminded constantly about the health risks. However, earlier research has shown that households very rarely refuse testing when this is offered for free, even when the results are posted on the wells (see for instance Madajewicz et al. 2007, Opar et al. 2007 and Bennear et al. 2013).

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