How can I find a leak in underground plumbing?
We did turn off the water last night and the power to the water pump and found that over a couple hours time we lost all the water in our reserve tank. Does this sound like a leak to you?


Maybe.  Was the reservoir tank cut off (like with a valve) from draining back down the well?  If there is a check valve, is it in good working order?  If not, it is hard to say whether the reservoir fed a leak or just emptied back into the well.

To more definitively indicate if well water is causing the observed ground water, turn off the pump, close all the water valves (to prevent water flowing out of the pump house) and wait.  Observe the ground water level every hour or two&mdash;maybe put in a stake or stick in the hole to better track it.  Does the water go down?  If so, a leak seems likely.

Leak detection

Doing a standard pipe pressure test would indicate quickly and conclusively identify whether there is a leak anywhere.  It requires containing the pipe under test by closing valves or disconnecting and capping pipe, adding a gauge or other measuring device, and pressurizing the pipe, perhaps with a bicycle tire pump&mdash;a gas pipe pressure testing gauge has an air valve for this purpose; I haven't seen anything directly comparable for water pipes.  Then just wait and watch.  The pressure should remain, dropping no more than 5% per hour.  (In my experience, temporary caps and a gauge for leak testing are the source of most pressure testing leaks.  Generously apply plumbers tape.)

Finding a leak

If a leak is detected, then there are several choices to fix it find it and fix it.  Which you choose depends on the specific situation, your budget, and your patience:


dig up all the pipe to inspect for leaks
abandon the existing pipe and install new
Sherlock Holmes


The first two are self-explanatory.  The third involves looking for clues.  Can you isolate part of the system&mdash;the hot water portion is an easy and obvious example&mdash;and see if leak continues?  Maybe there is another portion:  outdoor faucets, sprinkler system, barn, etc. which can be individually cut off from the main system.

A leak is most likely to develop at a pipe joint and the location of joints are reasonably predictable.  If the pipe is PVC for example, it usually comes in 10 foot lengths (at least in the U.S.&mdash;but if it is freezing where you are, probably you are south of the equator so some other length&mdash;3 m?&mdash;applies), so you only need dig a hole every pipe joint to check&mdash;at least with good luck.

Also consider any recent changes if it got worse:  Has a fence post been installed or did a tree fall?  Dig around there for to look for pipe.