The water we use for food production, watering lawns, bathing and toilet flushes is pumped from the fresh ground water, which is only about 0.76% of all water on earth.
When we use water, it will eventually, one way or the other, flow into the sea, where it turns into salt water. The evaporation from the sea will create clouds that will rain and seep down to become fresh ground water again.
The problem is that we are basically taking the tiniest bit and turning it into the largest faster than it can be replenished.