Come up with such showers and taps for the bathroom so that hot water comes at the right temperature as soon as you turn it on, and not so that you have to wait until it heats up – until warm water reaches through the pipes. Water stands still in the tube cooling down until you turn it on. Otherwise, a human gets a cold shock in the first 5-40 seconds (depending on the system) after one turned the water on.
Experienced people do not enter under the shower until they make sure the water is of right temperature. But this takes 5-40 seconds time each time to wait until water gets warm enough.
Especially actual this problem is for private houses, where the boiler may be quite on a distance from the shower and the tap. The 40 seconds may be quite real waiting time.