[LawTalkingGuy]

fwiw, both bloodletting and trepanning have legitimate modern forms.

In this case, where many for-profit companies were practicing dowsing it makes sense to ask if it might have worked. Probably, I agree, not because it fundamentally works, but as others in this thread have suggested - because practitioners unconsciously recognize the external signs of leaking pipes. This could match the the studies - actual randomized dowsing wouldn't work but standardized dowsing of the usual failing pipes could be easy.