Importance Of Water In The Body Water makes up about 55-60% of the body weight of an average human being. The lungs are nearly 90% water, blood is 83% water, brain and lean muscles are 75% water, bone is 22% water, and body fat is 10% water. Therefore, a person can survive for up to 4 weeks without food but no longer than 3 days without water. Water performs many vital functions in the body, it: moistens tissues such as those in the eyes, nose, and mouth, regulates body temperature, protects body organs and tissues, lubricates joints, helps prevent constipation, lessens the burden on liver and kidneys by flushing out waste products and toxins, transports nutrients and hormones around the body, and maintains the delicate balance of mineral concentrations within the cells. Every day you lose water through your breath, perspiration, urine, and bowel movements. For your body to function properly, you must replenish your water supply by consuming beverages and foods that cont