I was specifically questioning things like where is the hot water coming from, people without tubs can't figure out how to save water, etc. Those claims sound overly pessimistic and simplistic to me.
It is about conservation of water because as the person pointed out, you can't have a bunch of people running water continuously. You can store the water in a trash can or other large container. You can immerse yourself, or parts of yourself, in this water. You can even make a gravity shower to reuse the water since it's used for cooling and not cleaning. Replace the water when it gets too warm. This would greatly reduce the water usage compares to continual showers and provides a suitable substitute the previously mentioned bath tub when one is not available.
In some places people used to pump groundwater out of the ground to use. That water should be at a temperature of around 10-20C. So you could soak your feet in that to cool off.
