Less than 1% of the water supply on earth can be used as drinking water. About 6,800 gallons (25,700 liters) of water is required to grow a day's food for a family of four. A person can live about a month without food, but only about a week without water. If a human does not absorb enough water dehydration is the result. Most of the earth's surface water is permanently frozen or salty. If all the world's water were fit into a gallon jug , the fresh water available for us to use would equal only about one tablespoon When water contains a lot of calcium and magnesium, it is called hard water. Hard water is not suited for all purposes water is normally used for. An acre of corn will give off 4,000 gallons (15,000 liters) of water per day in evaporation. A small drip from a faucet can waste as much as 34 gallons or 128 liters of water a day. Of all the water on earth, only 2.5% is fresh water. Fresh water is either groundwater (0,5%), or readily accessible wa...