The pool light needs to be properly attached with the screw into the niche. This is a part of the bonding (safety) system for all lights. There should be a threaded hole near the top of the niche for the screw and a spot for the hook on the light to catch near the bottom. Water pressure DOES NOT hold them in. The screws are called "pilot" screws. If you don't have one, get it at a pool supply, not a hardware store. It must be stainless steel or brass.