I think they could do some things, in ancient times they collected rain water, why can't we do the same thing today? In agriculture they could use the drip method of irrigation so only just enough gets to the land and there is no run off. We don't need green lawns everywhere. Instead people could build rock gardens that look beautiful and use far less water. The best pollution and water purification system in the world is nature's own, swamps and marshes. But they are often drained because they are seen as a waste of space or a health hazard because they are a breeding ground for mosquitoes. But dirty and polluted water goes into swamps and marshes they can clean and depollute water better than any method science has come up with. Dirtly and polluted water enters the marsh and swamp systema and by the time it emerges it's clean water. Instead of building costly water reclamation systems that use a lot of energy, we could restore swamps and marshes and create new ones, once built they operate for free and give wildlife habitat. Swamps and marshes are havens for disease carrying misquitoes, but a combination of snails, fish, frogs, swallows and bats feed on mosquitoes during each phase of their life cycle and have been shown to keep mosquito popuation under control. But swallows and bats need mature trees to live but they will live in man-made swallow and bat houses until trees recover. Ironically, the hated bat eats the species of mosquito that only comes out at night and it is this night mosquito that carries most of the diseases that are harmful to man, so bats protect us from disease. We could dry wash our cars, then don't have to be shiny clean every day. Instead of dishwashers we could wash them in the sink. By letting them soak they need less water and detergent. After washing they can be rinsed by swishing them around in just a few inches of water to get rid of the detergent and then dried by hand to finish getting rid of the detergent instead of using gallons as the diswasher does. I'm sure there is a lot we can do, I don't think we need more fresh water, we need to use the fresh water we have more wisely.