Total Body Water percentage is the total amount of fluid in a person’s body expressed as a percentage of their total weight.

Water plays a vital role in many of the body’s processes and is found in every cell, tissue and organ, helping to regulate body temperature and eliminate waste. The body’s water levels naturally fluctuate throughout the day and night. Body water is continuously lost through urine, sweat and breathing and eating large meals, drinking alcohol, menstruation, illness, exercising, and bathing can cause variations in an individual’s hydration levels. 

Here you can find more information about body water.

Note: TBW percentage will tend to decrease as the percentage of body fat increases. An individual with a high percentage of body fat may fall below the average body water percentage. As body fat is lost, TBW percentage should gradually move towards the typical range given above

Every individual varies but as a guide the TBW percentage ranges for a healthy adult are:

Female: 45 to 60%  Male : 50 to 65%