Pictured here is a typical TPR (temperature-pressure-relief) valve, installed on all water heaters.  Code requires the installation of a ¾-inch solid pipe, discharging to the exterior or extending to within six (6) inches of the floor for safety reasons.  The TPR valve is designed to discharge high temperature and/or high pressure water if the water heater overheats or develops too much internal pressure.  Without a TPR valve, the water heater could literally blow up in the event of overheating or excessive pressure build-up.  The reason we extend the pipe is because, in the event that it discharges, we don’t want it discharging high pressure, high temperature water towards a person which would be a definite safety issue.   This was discovered at a recent home inspection on Shaw Island in the San Juan Islands.