Our main bathroom is approx 40 feet from the hot water tank. House is on a slab, well & septic. After heavy rains the water in this bathroom is lukewarm. My theory is that the hot water pipes are surrounded by cold groundwater, thus cooling it before it reaches its destination. My husband disagrees, assuming the pressure of the water would move it along fast enough that it would not cool this much. Does anyone have another theory or solution?