At a place I worked at long ago (a community of largish households) the people running it were very pro-dowser, and because they regularly needed new water sources they hired dowsers. For one well, they managed to get a bad hole in the edge of a swamp. The flow was surprisingly poor, and unsurprisingly murky, requiring that the entire system it fed into be chlorinated. For another they drilled and drilled, hitting a rock ledge that took days to get through, before the drill broke through, losing its very expensive rock head forever. The only up side of that was that it fell into a pool of water. Full of sulphur, but at least it was wet.
But faith is faith, and some people's answer to dowsing failures is to hire a different dowser.