Two neighboring wells may receive water from an underground reservoir called an aquifer. An aquifer holds its water in thousands of interconnected spaces in the rock, much like the pores in a sponge. When you pump water from one part of this aquifer, it reduces the water pressure in the neighboring well.
Whose water is it?
If two wells are drawing water from the same aquifer, who has rights to the water? The answer depends on where you live. In many states in the western U.S., the person who began using the water first has greater rights to continue using it. Historically, these laws meant that people had to use all of the water they were allowed, or risk having their water rights reduced. Such laws encourage water waste, and many of them have been amended.