Fluid balance records the amount of intake versus output to see if there is net gain or loss of fluid over a 24-hour period. Everything the patient drinks and passes as urine for 24 hours is measured and recorded on a fluid balance chart. The adult human body contains between 50 and 65% water, depending on body size. In very young infants, the average is about 75–78%, gradually declining to 65% by the age of one year. Humans gain and lose water constantly throughout the day. Humans gain water mainly through drinking at regular intervals throughout the day. Humans lose much of their daily fluids through urine output, but an important loss is also through the skin by evaporation of sweat. Young children also have a lower than adult's ability to concentrate urine, which again changes to near adult values by the age of 2 years, and they have less losses through sweating than adults.