In many places in the world, water is unclean b/c people take out the ecosystem that cleans it. Thus, the rivers only flow after rains and then go dry. When they do flow, they are filled with silt and all kinds of effluent. When people reserve the forests in the mountain highlands, they can go up into the forest and tap springs for fresh water.
This little youtube video
clip show low-tech, locally developed infrastructure to bring water from the mountains into the homes and businesses in the Rio Savegre valley shows just such a thing. The network of spring taps of which this is a part provides the Chacon families + some 13000 annual guests to their farms and ecotourist-oriented Savegre Mountain Hotel