Drinking water, also known as potable water, is water that is safe to drink or to use for food preparation. According to the World Health Organization, "access to safe drinking water is essential to health.

While food is important for the human body to function properly, the body’s need for water is far more crucial. A human being can survive without food for about five weeks, but only three to five days without water. The human body contains from 55% to 78% water, depending on body size. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors.  Most specialists agree that approximately 2 liters (6 to7 glasses) of water daily is the minimum to maintain proper body hydration, though medical literature favors a lower consumption level of 1 liter of water per day. The body’s water supply is involved in almost every body function: digestion, absorption, circulation, excretion and the transporting of nutrients throughout the body.

Water helps the body also:
Maintain normal temperature
Lubricate and cushion joints
Protect spinal cord and nerve endings
Prevents constipation

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Getting enough water every day is important for healthy people. Our fluid needs can be met by drinking water when thirsty and with meals. Bear in mind that some foods such as melons, celery, plums, peaches, and tomatoes help to supply this need also. As we age the sense of thirst reduces and our body’s water reserve shrinks. Drinking and replacing fluids lost through perspiration and elimination become ever more necessary to prevent dehydration.

Dehydration can be a serious problem for anyone, but children and older adults are at greater risk, according to the Gatorade Sports Science Institute. It offers these tips to avoid dehydration:

When exercising, drink early and often. Research shows exercise under warm or hot and humid conditions can cause dehydration in as little as 30 minutes. So it's important to consume fluids before, during and after exercise.
Don't wait until you're dehydrated to start drinking. Drinking in a dehydrated state can cause gastrointestinal distress.
The American College of Sports Medicine advises, 
to drink on a schedule.

Check the color of your urine. If your urine looks like the color of apple juice, you are probably dehydrated. If it looks more like the color of lemonade, you are probably well hydrated.

Without adequate water we can poison our systems with toxins that have not been properly eliminated from the body, thus creating built up in the body. Inadequate water in the body may contribute to excess body fat, poor muscle tone, poor functioning of body organs and water retention.  Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

The United States enjoys one of the world's most reliable and safest supplies of drinking water. Congress passed the Safe Drinking Water Act (SDWA) in 1974 to protect public health. The Safe Drinking Water Act (SDWA) requires the EPA to establish and enforce standards that public drinking water systems must follow.   
Humans require water with few impurities. Some solutes are acceptable and even desirable for taste enhancement, dental caries and to provide needed electrolytes. The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells, cisterns for rainwater harvesting, water supply networks, water purification facilities, water tanks, water towers, and water pipes including old aqueducts. The distribution of drinking water is done through municipal water systems, or as bottled water. Water may require purification for human consumption. This may involve removal of undissolved substances, dissolved substances, and harmful microbes. Popular methods are filtering with sand which only removes un-dissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid climates.

Bottled Water is regulated by the Food and Drug Administration. FDA follows EPA’s guidelines which define pure water as, bacterially safe. Water, depending on the area you live in should have a pH level 5.5-7.5. Because of the public’s concern over tap water another industry developed by providing bottled water. Bottled water is water which is sealed in bottle containers with no added ingredients other than optional an antimicrobial agent. The FDA defines the terms used to describe bottled water and they must be listed on the label.  Some forms of bottled water are:
Natural Spring

  “Water is the only drink for a wise man”  Henry Thoreau