What causes a pool pump from losing water pressure?

Your pool is "most" likely to lose water "while" the pump is running. First check the pump & pipes around the pump to make sure there is no visible water. If the leak isn't obvious, there is a good chance your pool is leaking from the skimmer, the skimmer face plates, the water jets, or several other locations. The following web site ("www.poolleak.com") helped me find several leaks in my pool and saved me the trouble and frustration of calling an expensive pool professional. Good luck. I have a leak that loses more water with the pump running. Had a leak guy out several days ago and he found the leak to be in my return line. Cost: $800.00 to replace the line. Includes digging up my concrete and replacing it.