Perhaps you should crack open that Econ 101 textbook first, because that same Econ 101 textbook would likely have water as the canonical example used to explain elasticity of demand. Demand for water is inelastic, both for agriculture and home use, so letting the "supply and demand curve" take care of it would likely cause a sharp increase in price in a very short period of time, which, from a policy perspective, seems like a terrible idea that would cause panic and economic instability.