Turbid or muddy water is not necessarily impure from a hygienic standpoint when found in rivers, but when subsoil water becomes turbid it should be regarded with suspicion. Hard and Soft Water The question of hard and soft water is one that must of necessity receive some consideration, but it is of more importance from an economic standpoint than from a sanitary standpoint. Soft water is generally considered to be more desirable for drinking purposes, and it is certainly more desirable for cooking. From an economical standpoint, soft water is more preferable as the hard water requires more soap to produce a lather. Hardness of water is spoken of as being temporary or permanent. If the water remains hard after having been boiled it is known as permanently hard water. Hardness of water is due to the presence of the soluble salts of the alkaline earth metals, especially calcium and magnesium. Temporary hardness is due to calcium or magnesium carbonate held in solution as a bicarbonate by the dissolved carbon dioxide. The hardness is temporary because the carbon dioxide is driven off by boiling, and the soluble bicarbonates are precipitated as insoluble carbonates. Permanent hardness, on the other hand, is due mainly to sulphates and chlorides of calcium or magnesium. These salts are stable and therefore are not precipitated by boiling. Elimination of Water from Body Water is excreted from the body through the various channels. The kidneys excrete about 50%, the lungs about 20%, the skin about 28%, while the other 2% is excreted through the feces and other minor channels. Amount of Water Needed for All Purposes The amount of water needed for all purposes varies just the same as the amount of water needed by the body varies with conditioning factors. The locality and the climate will enter into the consideration of the amount of water needed to meet the requirements of hygiene and sanitation. The amount of water required by the human body in twenty-four hours varies with many factors. The age of the individual and his occupation and health, and climate would be conditioning factors. However, authorities are pretty well agreed as to the amount necessary. It is estimated that the body requires a little less than one gallon of water per day, about two quarts taken as drinking water and the balance in food.