Every system in your body depends on water. We have power failures all the time. Cable TV goes out fairly frequently. But the water in any city or suburb is always there.
Water pressure is very reliable.
A big reason for that level of reliability is the water tower. You see water towers everywhere, especially if you live in a flat area full of small towns. Each water system has one or more towers. A water tower is an incredibly simple device. Water towers are tall to provide pressure.