An average family of four uses roughly 1200 liters (about 300 gallons) of water per day. (one liter = 1000 cm3.) How much depth would a lake lose per year if it uniformly covered an area of 43 square kilometers and supplied a local town with a population of 43000 people? Consider only population uses, and neglect evaporation, etc. Where do I even start? I thought of viewing it as a cylinder but, there is no height. uh?