How can I figure out where this pipe off my water main goes?

Question

From the street water main, I have three pipes coming off of it. Two go into the side of the house and one goes straight into the ground. How can I determine where the ground pipe goes or what it supplies? I’ve tried turning on all the faucets and spigots around the house and the ground pipe does not supply those. I was attempting to reduce the water pressure to my house, but I dumbly put the pressure gauge on a spigot that is outside of the pressure reducer. Now I could obviously use a wrench to remove the gauge, but now I’m curious what that pipe supplies. How can I figure out what that pipe is for?

Answer 1

Starting from the left.

The pipe going in the ground looks like PVC pipe and it probably going to the irrigation. It is not pressure regulated, so you might need a pressure regulator at the irrigation box.

The first pipe going into home is also not pressure regulated and it probably serves the water heater.

Answer 2

Typically irrigation or fire sprinkler supply.

Other than that speculation, you'll need to dig and see where it goes.

If a fire sprinkler, you'd expect it to enter the house, but not going through the pressure reducer is typical, and it might enter the house below grade.

Irrigation (lawn sprinklers, drippers, etc.) typically have some sort of valve bank controlling them this should lead to if that's it.