Clean drinking water is a natural renewable resource that easily replenishes itself so no we will never run out of water that is safe to drink.
Water is constantly being evaporated into the sky from sources such as oceans, lakes etc and new water is being produced in the sky naturally as well.
The earth sucks up the ocean water that is salty and then dumps it onto the ground in the form of rain and the ground then naturally filters that ocean salty water and other water from the sky and then it becomes safe to drink when it comes out of the ground through drinking water wells that are drilled into the earth.
Sometimes a water well will dry up but new and deeper ones can be drilled again until more clean drinking water is found.