Since cold water is drawn into a hot water heater at the same time that hot water is being drawn out, why doesn’t the water turn cold soon after you start taking a hot shower? — NG, Golden, Colorado
A hot water heater is built so that hot water is drawn out of its top and cold water enters it at its bottom. Since hot water is less dense than cold water, the hot water floats on the cold water and they don’t mix significantly. As you take your shower, you slowly deplete the hot water at the top of the tank and the level of cold water rises upward. But the shower doesn’t turn cold until almost all the hot water has left the tank and the cold water level has risen to its top.