They, in effect, cheat the system by using their ingenuity, which sometimes seems to me like an unfortunate human evolutionary mistake. This is a mixed blessing. People overwhelm nature s processes for purifying water. Pollutants released upstream, for example, do not have a chance to be filtered or otherwise removed before the water is used for drinking downstream. People change the surface of the Earth by clear-cutting forests, which leads to flooding.
People can sure be silly sometimes.
Most of the water used in homes and business is for washing and flushing away undesired materials. Water is used to take away waste heat at power plants. Nature would never use water in such a wasteful manner. If people use the resources they have efficiently, by not using excessive water for flower gardens, lawns, and washing cars, then we can reduce our demand on nature. It seems to me, though, that many people will need to learn this the hard way.