Introduction: Arsenic (As) in drinking water affects the health of hundreds of millions of people worldwide. Although West Bengal, Bangladesh and Taiwan are among the most affected regions, with As concentration as high as 4,700 μg/L and where levels >300 μg/L are common, As contamination of well water is also prevalent across the US and Canada. Studies of populations exposed to such high levels show strong associations and dose-response relationships with As in drinking water and a wide range of illness, including, skin, lung, bladder, and kidney cancer. The threshold at which these diseases develop is uncertain at lower levels of exposure. Recent evidence suggests possible health effects at levels as low as 10 μg/L, current World Health Organization advisory limit. This study models the risk of developing bladder/kidney cancer in those exposed to As around current guideline levels. Methods: A Bayesian spatial autoregressive model was used to model risk at 3 levels of As exposure (0–2 μg/L; 2–5 μg/L; >5 μg/L—based on 10,498 private well samples) in 864 bladder and 525 kidney cancer cases diagnosed in Nova Scotia Canada, between 1998-2010. The model accounted for spatial dependencies and included covariates (e.g. smoking proxies). Results: The risk of developing bladder cancer (both sex) was on average 16 % (2–5 µg/L) and 18 % (> 5 µg/L) greater than that of the referent group (< 2 µg/L), with associated posterior probabilities of 0.88 and 0.93 for these risks being greater than the reference rate. Effect sizes for kidney cancer were lower; the risk being on average 5 % (2–5 µg/L) and 14 % (> 5 µg/L) greater than that of the referent group, with associated probabilities of 0.66 and 0.87. Stratified analyses by sex, showed larger posterior probabilities for an increased risk amongst males– a result likely due to low female case counts. Conclusion: This study provides evidence for health effects at low level of As exposure in drinking water.