Concrete or fiberglass shell in-ground swimming pools are typically equipped with hydrostatic relief valves. A hydrostatic relief valve sits in a swimming pool's deepest part, usually under its main drain cover. Swimming pool hydrostatic valves keep the pressure between pool water and the groundwater beneath the pool equalized. Worn out swimming pool hydrostatic valves are the most common causes of in-ground swimming pool leaks. Swimming pool hydrostatic relief valves should be replaced every five years to prevent leakage.
In-ground swimming pool plumbing systems are a collection of pipes, hoses, pumps, filters and water return ports. Unfortunately, a water leak can develop in an in-ground pool's plumbing system from time to time. Fortunately, most leaks in an in-ground pool's plumbing system occur at visible points near the pump and filter. In-ground pool pump water lines and fittings occasionally develop leaks as they expand and contract. Periodically inspect visible areas of an in-ground swimming pool's plumbing system to identify possible leakage.
In-ground swimming pools have basins that hold their water in. Only three types of in-ground swimming pool basins are used: vinyl liner, concrete or fiberglass shell. Vinyl liner in-ground swimming pools can develop leaks from rips, holes or tears in their liners. Concrete and fiberglass shell in-ground pools may leak due to cracks in their basins. Locate in-ground swimming pool basin leaks by using a syringe or even a turkey baster to inject food-colored dye into the water near a suspected leak.
Underground water leaks in in-ground swimming pools are very difficult to find; usually a pool professional is required to do so. Worn-out swimming pool fittings around water returns, skimmers and ladders are occasional sources of leaks, too. Leaky in-ground swimming pool vinyl liners can often be patched using underwater patch kits. Repairing leaky concrete or fiberglass in-ground pool basins is a bit more involved, and draining the pool is sometimes required.