Flow tests: how much water does your well really give you?

Quality is only half of a well's story. The other half is quantity: the sustained rate, in gallons per minute, that the well can supply without running dry. A flow test measures that rate over a period of time, usually by running water at a steady rate and watching the pressure and, where it can be reached, the water level.

Flow tests are especially useful before buying a house. A listing can say "drilled well" and tell you nothing about whether the well keeps up with a family of five, a washing machine and a lawn sprinkler. They also help when an older well seems to be going dry in late summer, or when a new addition adds demand.

The result tells you whether the well, pump and tank are matched, and whether storage or a larger pressure tank can cover the shortfall.