Why do you have to wait for hot water after someone just took a shower?

Answer 1

When someone takes a shower, the hot water tank replaces the water used with cold water. It takes the hot water heater some time (which varies with each heater) to heat the newly filled tank. The hot water is always replaced by cold as you use it, but you don't notice it as much when you use smaller amounts or, like dishwashers and washing machines, use the hot water in intermittent amounts.