Water - Have You had a Glass or Two Today
~ October 2005 No.198 ~
Every day we need water. Without it we would soon die. For most of us, drinking water comes so naturally that we probably don’t even realize how much we consume each day. Whether it is just water, or tea, coffee, or fruit juice, we get our daily intake of H2O in many ways.
Although it is not obvious, we have three main sources of water. The liquids we drink, the water that is a part of every food we eat, and then there is what is called “metabolic water”. Many of the chemical reactions that are taking place in our bodies that enable us to live and grow also produce water as an end-product. Although not as large as the water we get from what we eat and drink, metabolic water is nonetheless important.
In temperate climates we need about 2 litres of water a day depending on our activity level. Strenuous exercise on hot humid days can cause a loss of up to 10 litres of water. Although severe dehydration is not common, mild dehydration can be a hazard for people who carry out activities that cause them to produce large quantities of sweat. But, even as we breathe, we lose water, as anyone who goes outside on a cold winter day knows. The digestion of our food also requires a great deal of water. Fortunately, in the large intestine most of this water is reabsorbed into the body. But some water does leave the body in fecal material.
The type of diet we eat can also affect how much water we need each day. People on high protein diets are told to increase their water intake as a way of getting rid of higher levels of waste products produced while on these diets. The digestive system of children also is more dependent on water for proper functioning.
When we perspire we lose salt (NaCl) as well as water. Drinking liquids with added salt is preferred to just drinking plain water after vigorous exercise. Simply drinking the same volume of pure water equal to the volume of perspiration lost can lead to an imbalance in salt concentration at the cellular level. This is particularly dangerous in older people who have hypertension or heart disease. Seniors should closely regulate their daily water intake, and moderately increase their salt intake when they sweat.
Our bodies have a finely tuned mechanism for maintaining the proper concentration of salt in our body fluids such as blood and urine. If your water intake goes down, your urine output does down and urine salt concentration goes up. Over the long term this can cause a stress on the kidneys and should be avoided. After drinking large amounts of fluids, urine volume goes up but salt concentration goes down.
Although it does not appear on a list of required nutrients, water is something that we need every day to remain healthy
Basic Water Requirements for Human Activities: Meeting Basic Needs
Water Intl 1996,21:83-92