Ok but here is the thing, Japan had great civil engineering for 100 years, they have made lots and lots and lots of tunnels. Japan overall has fantastic water quality and is globally known for clean and safe bathrooms.

So the argument that 'new train X will destroy the water supply' really needs to be based on a whole stack of good evidence.

Hard to imagine how a train that has no emissions itself as its catenary powered causes your water supply to be unclean.