Drinking water

Drinking water, or potable water, is water that is safe to consume, whether drunk directly or used in cooking. When it comes from a tap, it is also called tap water. How much a person needs to stay healthy varies based on factors like physical activity, age, health conditions, and the environment. For example, someone working in a hot climate might require up to 16 liters (4.2 U.S. gallons) per day. Globally, around two billion people do not have access to safe drinking water. Unsafe water can carry diseases and is a leading cause of illness and death, especially in developing countries.

Potable water is available in most populated areas, though it can be expensive and the supply may not always be sustainable. Common sources include springs, groundwater from aquifers and hyporheic zones, rainwater harvesting, surface water from rivers, streams, and glaciers, and desalinated seawater. For these to be safe, they must be treated and meet quality standards. An experimental source is solar-powered atmospheric water generators. Bottled water is another source, often used when people distrust other supplies; most bottled water is simply packaged tap water, though some comes from springs.

The most efficient way to deliver drinking water is through pipes, but plumbing requires significant investment and can have high operating costs. Replacing aging water and sanitation infrastructure in industrialized countries may cost up to $200 billion per year. Leaks from pipes, which can lose 50% of water in urban systems, reduce access. Tap water is delivered to homes through domestic water systems.

In the United States, average home water use per person is 69.3 U.S. gallons (262 liters) per day, but only 1% of that is for drinking and cooking. The rest goes to toilets, washing machines, showers, baths, faucets, and leaks. Recommended daily water intake varies. In the U.S., adequate intake for total water (from drinks and food) is 4.0 liters per day for men over 18 and 3.0 liters for women over 18, assuming about 80% comes from drinks. The European Food Safety Authority recommends 2.0 liters per day for women and 2.5 liters for men. The common advice to drink eight glasses (about 1.9 liters) of plain water daily is not scientifically supported; thirst is a better guide. Americans aged 21 and older average 1,043 mL of drinking water per day, with 95% drinking less than 2,958 mL. Active people in hot climates may need 6.0 liters or more per day.

How much drinking water contributes to mineral intake is unclear. Inorganic minerals enter water from runoff and groundwater, and treatment adds minerals like calcium, zinc, manganese, phosphate, fluoride, and sodium. While some animals get significant water from metabolism, humans get only a small fraction that way. Trace elements like sodium, potassium, and chloride are common in small amounts; fluoride, beneficial in low concentrations, can cause problems at high levels. Fluid balance is crucial; heavy sweating may require replacing electrolytes, while drinking too much water too quickly can cause hyponatremia, which can be fatal. Water makes up about 60% of body weight in men, 55% in women, 70–80% in babies, and about 45% in older people.

For domesticated animals, water needs are studied in animal husbandry. A dairy cow might need 35 U.S. gallons (130 liters) per day, a horse about a third of that, and a hog about a tenth. Few studies focus on wild animals' drinking behavior.

According to a 2017 WHO report, safe drinking water is water that poses no significant health risk over a lifetime, accounting for different sensitivities. A UNICEF and UNESCO report states Finland has the best drinking water quality in the world. Quality is monitored through three categories: microbiological (e.g., coliform bacteria, E. coli, cholera-causing Vibrio cholerae, viruses, and protozoan parasites), chemical, and physical. Originally, fecal contamination was detected by the presence of coliform bacteria.