water table
water level
groundwater level

He says the problem is the water table has fallen too low.

This of course led to problems with the water table.

Do your people think it's going to get in the water table?

It couldn't be the water table, because the site was higher than the rest of the garden.

Then she led him by the hand to the water table.

He could just look at a landscape and tell you how far down the water table was.

But what if there was a water table near the surface?

In this area the water table is very close to the surface.

The water table was generally only two feet down before the impact.

How could I put chemicals into the air and ground, maybe the water table?