The Eastern Townships (ETR) is a region in Québec (Canada) where the soil is naturally rich in arsenic (As). About a third of the people in the ETR obtain their water from a private well. A quasi-experimental design was used to compare two campaigns designed to promote As screening in well water: a mass-media campaign (MMC) followed or not by a community-based intervention (CBI). The MMC is based on a press release issued for the ETR, along with a leaflet on As made available on the Internet, and in strategic places. The CBI, formulated according to the factors of the Precede-Proceed model, was aimed at mobilizing local authorities and small media. It targets only one municipality; the intervention community (IC). Using a separate pre-post samples design, two population-based cross-sectional (pre-CBI and post-CBI) surveys were conducted by phone at 6-month intervals, by means of random samples. The samples counted, for the IC and the ETR, respectively, 87 and 156 well owners in pre-CBI, and 106 and 190 in post-CBI. The results in post-CBI showed that the proportion of well owners who had their water test increased by four times in the IC after (16% p = 0.004). When adjusting for age and gender among all the post-CBI respondents, As screening is related with intervention status (exposed to MMC and CBI; p ≤ 0.001) and on previous microbiological water analysis behavior (p ≤ 0.05), but is not related to knowledge. This study demonstrates the superiority of a community-based campaign over a MMC when environmental health is concerned.