Humans can exist for several weeks without food; however, after several days without water, we would not survive. Water is one of the most essential elements in the body; in fact, it is the most abundant substance in the human body and is a major component of every cell.
Water is the basis of all bodily fluids; it is vital for the functioning of tissues, organs and bodily systems. Blood, lymph, and other fluids move between the cells and through the vessels, bringing energy, carrying away wastes, regulating temperature, bringing disease fighters, and carrying hormonal information from one area to another.
Circulation
Blood is composed of blood cells suspended in a liquid known as blood plasma, which constitutes 55% of blood fluids, and is mostly water (92% by volume). The water portion of blood dissolves and carries necessary substances such as nutrients and oxygen to the cells, transporting metabolic waste products away from those same cells.
There are two types of blood vessels that carry blood throughout our bodies; one of which are arteries, which carry oxygenated blood from the heart to the rest of the body. Blood also travels through veins back to the heart and lungs, where it receives more oxygen. As the heart beats, you can feel blood traveling through the body at pulse points—such as the neck and the wrist—where large blood-filled arteries run close to the surface of the skin.
Water is a necessary ingredient for proper blood flow in the body. As you drink more water, oxygen levels in your bloodstream increase, leading to better circulation and improved overall health. Good blood flow can help increase your energy levels and burn more fat.
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Digestion
Gastric juices are liquids found in the stomach; in their normal state, these liquids are usually primarily clear in color. The juices in the stomach begin the process of breaking down food so that nutrients can be extracted by the intestines; they are produced by glands in the stomach as needed. Acids and enzymes that are in the stomach need the balance of water to break down food into a homogenized fluid. Once the fluid is formed, it can be easily passed into the intestine for the next stage of digestion.
Water consumption plays an important role in the digestion of solid foods; an acidic stomach will respond to hydration, and therefore make it easier to digest food. Sometimes, an absence of water in the body may lead to common symptoms such as heartburn and constipation.
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the kidneys through urine, and the skin through sweat.
Urine is a liquid waste product of the body secreted by the kidney by a process of filtration from blood known as urination and excreted by the urethra. Urine production serves a greater purpose than just dumping excess water from the body; it is actually composed of 95% water, which works as a vehicle to carry the waste of urea, uric acid, ammonia, hormones, dead blood cells, salts and minerals, and toxins out of the body.
Sweating, on the other hand, is the release of a fluid consisting primarily of water as well as minerals, lactate, and urea from the body's sweat glands in the skin; this process is also known as perspiration. Sweating is an essential function that helps the body stay cool.
The kidneys act as a filter, but for them to work properly they need to have plenty of water intake. Water lessens the burden on the kidneys and liver by flushing out waste products as it dilutes the calcium in our urine, which could crystallize to form kidney stones if the body did not receive enough fluids. Drinking water keeps the body hydrated by replenishing the bodily fluids lost through urination or sweating.
References
dhammacenter.org
helpwithcooking.com
fitness.com
dirjournal.com
wisegeek.com