Check the pressure relief valve on the hot water tank. sometimes these valves are plumbed directly into a drain and may be leaking without your knowledge. If you can't remove the drain pipe to check for a leak listen foรขโ‚ฌยฆ check the toilet for leaks by removing the top off the tank and listening very closely. if you hear any hissing at all, try to locate where it is coming from. if you locate the area where the leak is coming from, assess it and determine if yรขโ‚ฌยฆ