People interact with Earth’s water (hydrosphere) in a variety of ways. We depend upon water for survival, but we also need it to keep clean and help avoid spreading disease. On our ever-changing Earth, the supply of fresh water can be limited for some humans. We need good techniques to make the best use of the fresh water we do have. For example, when you wash your hands, how do you do it? With soap and water? With water alone? Do you scrub your hands or simply rinse them under the faucet? Does it even matter? Yes, it does!