Adding water to urine dilutes the pigments urine contains, which lightens the color. Urine generally contains only urea, amino acids and other waste products that are not highly reactive with water.
Urine is usually yellow, but may become red, brown or other colors if the individual ingests certain things or has certain health problems. Water is a very stable liquid that mainly reacts with alkali metals, such as lithium, and alkaline earth metals, such as radium. If the water contains large amounts of chlorine or other disinfectants, such as the water in swimming pools, mixing it with urine forms various organic compounds that spread through the air and negatively affect health.