I checked my water line a few years ago and I could get an amp if I turned off all the breakers on one leg. 3 Amps on the ground sounds high. That would make me think that a neighbour has a broken neutral.
3 Amps on the ground would be a 60 ohm resistance assuming 120 volts (E = I x R). That sounds like a hot tied to a ground rod or maybe a light pole.
Do you use ground rods and bond the water line and jumper the water meter?
