Water - why do we need it?
Water is a critical ingredient forf humans, animals and plants. Although humans can live without food for several days or weeks, they can only live a few days without water. Water, therefore, must be replenished often in order to fulfil its numerous bodily functions.
Water makes up more than two-thirds of the weight of the human body, with the brain being 70% water and the lungs nearly 90% water. All cells and organs need water to function.
What do we need water for?
Lubrication and protection.
Water is the main ingredient of all body fluids. Blood, lymph, saliva, cerebrospinal fluid, synovial fluid, bile and other protective fluids throughout the body are all predominantly water. Water is also essential for waste removal through sweating, urination and bowel movements, and helps to prevent and relieve constipation.
Body temperature regulation
Water has a high heat capacity, which means it requires more energy than many other substances to increase its temperature. Because the body is constituted mainly of water, it takes a large amount of energy to raise or lower one's body temperature, therefore allowing the body to maintain a relatively stable body temperature. When body temperature rises (for example due to exercise, illness, environmental factors), the autonomic nervous system triggers the production of sweat. The sweat evaporates off the skin, cooling the body, and allowing maintenance of homeostasis.
Electrolyte regulation
All cells require electrolytes in order to function. Electrolytes are ions that conduct electric currents from cell to cell and include sodium, chloride and potassium. Electrolyte levels must be precisely balanced in order to maintain optimum function. The autonomic nervous system activates excretion of water or triggers the thirst mechanism in order to maintain precise electrolyte levels.
Maintenance of pH
pH balance is essential for the body to undertake chemical and metabolic reactions at optimum levels.
What happens if we have too little water?
We can survive without food for a few weeks, but only a few days without water. Dehydration (lack of water) reduces the amount of blood in your circulatory system, increasing pressure on the heart to deliver oxygen-loaded cells to your muscles.
When you start to become dehydrated you may experience dizziness, headaches, and become irritable. As dehydration progresses you start to become clumsy, exhausted and begin experiencing hallucinations. You may become nauseous and start vomiting, and your eye-sight begins to deteriorate. Eventually you will descend into a coma and die.
What happens if we hold onto too much water?
Hyponatraemia is a condition that develops when you retain too much water; excess water floods the cells and causes them to swell. Because of the imbalance in electrolytes and pH, brain function deteriorates affecting chemical reactions and metabolism. Symptoms include headache, nausea, muscle cramps, confusion, and fatigue. Eventually you will descend into coma and die.
So how can we get the right amount of water?
It is recommended that the daily water intake for adults is 2.7 to 3.7 litres.
However, this will depend on a variety of factors including weight, age, activity level and fitness, as well as any medical conditions you may have. This amount is the total intake form both food and fluids; interestingly there is no specific recommendation for how much water you should drink.
If you drink fluids when you feel thirsty and with meals, you should get enough water to keep you hydrated. You can get water through liquid foods and beverages, such as soup, milk, tea, coffee, soda, drinking water, and juices.
Alcohol is not a good source of water because it is a diuretic and causes the body to release water. Try to avoid sweetened and fizzy drinks due to the high calorific levels and impact on your teeth.
The best way to determine if you are drinking the right amount of fluids is to check the colour of your urine.
Healthy pee is 1-3, 4-8 you need to hydrate.
References
Bedford Hospital NHS Trust (undated) Keeping hydrated. (online at www.bedfordhospital.nhs.uk [Accessed 27/03/2017].
El-Buri H (2015) Why Do We Need Water in Our Diet? (online at www.livestrong.com) [Accessed 27/03/2017].
Margolis RE (undated) Why do we need to drink water (online at //healthyeating.sfgate.com/need-drink-water-4301.html) [Accessed 27/-03/2017].
Unknown (2017) Water in diet. (online at medlineplus.gov/) [Accessed 27/03/2017].