In addition to stopping wasting our precious water, one useful step we should take is to 36 ways of reusing it. Today, in most large cities, water is used only 37 and it eventually returns to the sea or runs into underground storage tanks, But it is 38 to pipe water that has been used to a purifying(净化) plant, There it can be filtered and treated with chemicals so that it can be used again just as if it were fresh from a spring.