Drinking water

Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often supplied through taps, in which case it is also called tap water.
The amount of drinking water required to maintain good health varies, and depends on physical activity, age, health-related issues, and environmental conditions. For those who work in a hot climate, up to a day may be required.
As many as two billion people lack safe drinking water. Water can carry vectors of disease and is a major cause of death and illness worldwide. Developing countries are most affected by unsafe drinking water.

Supply

The most efficient and convenient way to transport potable water is through pipes. Plumbing can require significant capital investment. Some systems suffer high operating costs. The cost to replace the deteriorating water and sanitation infrastructure of industrialized countries may be as high as $200 billion a year. Leakage of untreated and treated water from pipes reduces access to water. Leakage rates of 50% are not uncommon in urban systems.
Tap water, delivered by domestic water systems refers to water piped to homes and delivered to a tap or spigot.

Quantity

Usage for general household use

In the United States, the typical water consumption per capita, at home, is of water per day. Of this, only 1% of the water provided by public water suppliers is for drinking and cooking. Uses include toilets, washing machines, showers, baths, faucets, and leaks.

Usage for drinking

Animals

The qualitative and quantitative aspects of drinking water requirements on domesticated animals are examined within the context of animal husbandry. For example, a farmer might plan for per day for a dairy cow, a third of that for a horse, and a tenth of that for a hog.
However, relatively few studies have been focused on the drinking behavior of wild animals.

Quality

According to a 2017 World Health Organization report, safe ''drinking water'' is water that "does not represent any significant risk to health over a lifetime of consumption, including different sensitivities that may occur between life stages".
According to a report by UNICEF and UNESCO, Finland has the best drinking water quality in the world.

Parameters to monitor quality

Parameters for drinking water quality typically fall within three categories: microbiological, chemical and physical.
Microbiological parameters include coliform bacteria, E. coli, and specific pathogenic species of bacteria, viruses and protozoan parasites. Originally, fecal contamination was determined with the presence of coliform bacteria, a convenient marker for a class of harmful fecal pathogens. The presence of fecal coliforms serves as an indication of contamination by sewage. Additional contaminants include protozoan oocysts such as Cryptosporidium sp., Giardia lamblia, Legionella, and viruses. Microbial pathogenic parameters are typically of greatest concern because of their immediate health risk.
Physical and chemical parameters include heavy metals, trace organic compounds, total suspended solids and turbidity. Chemical parameters tend to pose more of a chronic health risk through buildup of heavy metals although some components like nitrates/nitrites and arsenic can have a more immediate impact. Physical parameters affect the aesthetics and taste of the drinking water and may complicate the removal of microbial pathogens.
Pesticides are also potential drinking water contaminants of the category chemical contaminants. Pesticides may be present in drinking water in low concentrations, but the toxicity of the chemical and the extent of human exposure are factors that are used to determine the specific health risk.
Perfluorinated alkylated substances are a group of synthetic compounds used in a large variety of consumer products, such as food packaging, waterproof fabrics, carpeting and cookware. PFAS are known to persist in the environment and are commonly described as persistent organic pollutants. PFAS chemicals have been detected in blood, both humans and animals, worldwide, as well as in food products, water, air and soil. Animal testing studies with PFAS have shown effects on growth and development, and possibly effects on reproduction, thyroid, the immune system and liver. As of 2022 the health impacts of many PFAS compounds are not understood. Scientists are conducting research to determine the extent and severity of impacts from PFAS on human health. PFAS have been widely detected in drinking water worldwide and regulations have been developed, or are under development, in many countries.The U.S. Environmental Protection Agency has published laboratory test methods for PFAS compounds.

Drinking water quality standards

Health issues due to low quality

The World Health Organization considers access to safe drinking-water a basic human right.
Contaminated water is estimated to result in more than half a million deaths per year. More people die from unsafe water than from war, then-U.N. secretary-general Ban Ki-moon said in 2010. Contaminated water together with the lack of sanitation was estimated to cause about one percent of disability adjusted life years worldwide in 2010. According to the WHO, the most common diseases linked with poor water quality are cholera, diarrhea, dysentery, hepatitis A, typhoid, and polio.
One of the main causes for contaminated drinking water in developing countries is lack of sanitation and poor hygiene. For this reason, the quantification of the burden of disease from consuming contaminated drinking water usually looks at water, sanitation and hygiene aspects together. The acronym for this is WASH - standing for water, sanitation and hygiene.

Diarrhea, malnutrition and stunting

Consumption of contaminated groundwater

Sixty million people are estimated to have been poisoned by well water contaminated by excessive fluoride, which dissolved from granite rocks. The effects are particularly evident in the bone deformations of children. Similar or larger problems are anticipated in other countries including China, Uzbekistan, and Ethiopia. Although helpful for dental health in low dosage, fluoride in large amounts interferes with bone formation.
Long-term consumption of water with high fluoride concentration can have serious undesirable consequences such as dental fluorosis, enamel mottle and skeletal fluorosis, bone deformities in children. Fluorosis severity depends on how much fluoride is present in the water, as well as people's diet and physical activity. Defluoridation methods include membrane-based methods, precipitation, absorption, and electrocoagulation.
Natural arsenic contamination of groundwater is a global threat with 140 million people affected in 70 countries globally.

Examples of poor drinking water quality incidents

Some examples of water quality problems with drinking water supplies include:

In 1854, a cholera outbreak in London's Soho district was identified by John Snow as originating from contaminated water from the Broad Street pump. This was a founding event of the science of epidemiology.
Contamination of groundwater with arsenic in Bangladesh; the largest-scale mass poisoning of a population
Hinkley groundwater contamination.
Walkerton E. coli outbreak. In 2000, an E. coli outbreak occurred in Walkerton, Ontario, Canada. Seven people died from drinking contaminated water. Hundreds suffered from the symptoms of the disease.
Flint water crisis
Jackson, Mississippi water crisis, United States
In 1987, a cryptosporidiosis outbreak in western Georgia
In 1993, Milwaukee Cryptosporidium outbreak
In 1998, an outbreak of typhoid fever in northern Israel, which was associated with the contaminated municipal water supply
In 1997, 369 cases of cryptosporidiosis occurred, caused by a contaminated fountain in the Minnesota zoo. Most of the sufferers were children
In 1998, a non-chlorinated municipal water supply was blamed for a campylobacteriosis outbreak in northern Finland
In 2000, a gastroenteritis outbreak that was brought by a non-chlorinated community water supply, in southern Finland
In 2004, contamination of the community water supply, serving the Bergen city centre of Norway, was later reported after the outbreak of waterborne giardiasis
In 2007, contaminated drinking water was pinpointed which had led to the outbreak of gastroenteritis with multiple aetiologies in Denmark

Examples of chemical contamination include:

In 1988 many people were poisoned in Camelford, when a worker put 20 tonnes of aluminium sulphate coagulant in the wrong tank.
In 1993 a fluoride poisoning outbreak resulting from overfeeding of fluoride, in Mississippi.
In 2007 the water supply of Spencer, Massachusetts became contaminated with excess sodium hydroxide when its treatment equipment malfunctioned.
In 2019 electric transformer oil entered the water supply for the city of Uummannaq in Greenland. A cargo ship in harbour was able to maintain a minimum supply to the city for two days until the mains supply was restored and flushing of all the pipework was started.
Treatment

Most water requires some treatment before use; even water from deep wells or springs. The extent of treatment depends on the source of the water. Appropriate technology options in water treatment include both community-scale and household-scale point-of-use designs. Only a few large urban areas such as Christchurch, New Zealand have access to sufficiently pure water of sufficient volume that no treatment of the raw water is required.
In emergency situations when conventional treatment systems have been compromised, waterborne pathogens may be killed or inactivated by boiling but this requires abundant sources of fuel, and can be very onerous on consumers, especially where it is difficult to store boiled water in sterile conditions. Other techniques, such as filtration, chemical disinfection, and exposure to ultraviolet radiation have been demonstrated in an array of randomized control trials to significantly reduce levels of water-borne disease among users in low-income countries, but these suffer from the same problems as boiling methods.
Another type of water treatment is called desalination and is used mainly in dry areas with access to large bodies of saltwater.
Publicly available treated water has historically been associated with major increases in life expectancy and improved public health. Water disinfection can greatly reduce the risks of waterborne diseases such as typhoid and cholera. Chlorination is currently the most widely used water disinfection method, although chlorine compounds can react with substances in water and produce disinfection by-products that pose problems to human health. Local geological conditions affecting groundwater are determining factors for the presence of various metal ions, often rendering the water "soft" or "hard".
In the event of contamination of drinking water, government officials typically issue an advisory regarding water consumption. In the case of biological contamination, residents are usually advised to boil their water before consumption or to use bottled water as an alternative. In the case of chemical contamination, residents may be advised to refrain from consuming tap water entirely until the matter is resolved.