Leak detection is important for a multitude of factors. Leaks mean your well pump(s) are running more often which reduces their life. It means an increased risk of harmful bacteria entering your water system. It means lower static levels in your well(s) which not only means the possibility of issuing water restrictions for your customers, but the possibility of your wells running dry.
If you're an operator of a water system or an association, I offer full leak detection surveys using state of the art ground microphones. The survey will consist of getting the approximate gallons per day/gallons per minute leakage as well as any water system maps that are available from the client. The more information I have going into a survey means less time looking for and digging up curb stops and more time listening for leaks.
The process starts with listening to each known and found system valve and service curbstops. Any loud spots are potential leaks and will be noted, staked and/or painted. If nothing is found on the initial survey, I will then walk the water main listening to the ground every 5 feet using a probe if necessary.
Leaks can be tricky and aren't always eager to be made known. Success largely depends on leak size, leak type, as well as the underground discharge point. For example, leaks spraying into an underwater cavern of it's own making are notoriously difficult to hear.
If this is the case, I will suggest working with your operator or a company to put compressed air to the lines. Sometimes this will force a leak to the surface but for my purposes, forces sound through the leak so that my equipment can detect it.