I wonder about this a lot. Billions of people drinking, showering, running dishwasher, flushing toilet. How the heck do we have enough freshwater to sustain this for so long?
It’s not like almost all of the water goes anywhere, even when drinking it, you eventually pee, sweat it out, etc.
Afterwards it goes back to the cycle, can evaporate and rain again.
Water is like an infinite resource, since we never really destroy it, we just use it and use it again.
Specifically, about 14 million gallons of precipitation falls on the earth every year *per person*! A lot of that is inaccessible, falling over oceans or whatnot, and a lot we want to leave to nature. But you might need a couple hundred thousand at most, and that’s accounting for agriculture on your behalf, so hopefully that gives you a sense of the scale that nature provides.
The water cycle. Water is constantly evaporating from the ocean; just like distillation, it leaves the salt behind. That water eventually falls as rain replenishing rivers and lakes with fresh, unsalty, water.
We also treat domestic wastewater and return it to the environment.