My uncle Louie considered himself a skilled dowser. 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. Just walk slowly and the rods should suddenly go askew when you walk over the buried water pipes. 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.