Excretion - Kidneys use sodium levels to guide the rate of water excretion. Also, the kidneys may be directed by a pituitary gland hormone to conserve water. Rapid dehydration can be fatal, as the body may not be able to respond to the need in time. Hard ' or ' soft ' water refers to the amount of dissolved solids. Hard water is high in Magnesium and Calcium salts usually because t originates in underground locations where these salts are present.
Hard water leaves a ring around the bathtub because of precipitation with soap.
Soft water, such as rainwater, has much lower dissolved solids and should not leave a residue with soap. Bottled water i s commercially available at different prices, and is usually made by 'deionizing', or removing dissolved solids from the water through reverse osmosis or ion exchange processes. Some bottled water arises from natural sources such as springs, and is sold at premium prices. 290 Body water is contained in cells, exists in extracellular spaces, and fills the blood vessels. These three locations for water are in equilibrium in the body, and water molecules move back and forth from location to location.