My uncle Louie considered himself a skilled dowser. I am a Professor of Exploration Geophysics so you might expect me to be skeptical, but I believe my uncle Louie could find water by dowsing.
Uncle Louie improved upon the traditional method of using willow twigs. He used bent welding rods. Willow twigs are long and slim. Welding rods have more mass and are even slimmer. He would bend ends of the welding rods down at a 90 degree angle. Then the rods look like this:
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Grabbing each rod below the bend,
he held two slightly unstable inverted pendulums.
Just walk slowly and the rods should suddenly
go askew when you walk over the buried water pipes.
Dowsing for water pipes could sometimes work this way: When those pipes were buried, someone had to guess how much dirt to throw back into the trench. The dirt settles slowly, in early years bulging up, and in later years settling below the normal ground level. After the grass grows over it all, you cannot see the surface bumps and dips, but the inverted pendulums can.
I could also see the location of uncle Louie's underground pipes where they ran beneath his garden. The backfilled soil contained more clay and less humus (because few people backfill carefully enough to restore all the humus near the surface) so his garden was less vigorous over the ancient water-pipe trench.