Drinking water or potable water is water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually consumed or used in food preparation.
Over large parts of the world, humans have inadequate access to potable water and use sources contaminated with disease vectors, pathogens or unacceptable levels of dissolved chemicals or suspended solids. Such water is not potable and drinking or using such water in food preparation leads to widespread acute and chronic illnesses and is a major cause of death in many countries. Reduction of waterborne diseases is a major public health goal in developing countries.
Typically, water supply networks deliver potable water, whether it is to be used for drinking, washing or landscape irrigation. One counterexample is urban China, where drinking water can optionally be delivered by a separate tap.
Essential to the survival of all organisms, water has always been an important and life-sustaining drink to humans. Excluding fat, water composes approximately 70% of the human body by mass. It is a crucial component of metabolic processes and serves as a solvent for many bodily solutes.Health authorities have historically suggested at least eight glasses, eight fluid ounces each (168 ml), of water per day (64 fluid ounces, or 1.89 litres), and the British Dietetic Association recommends 1.8 litres. The United States Environmental Protection Agency has determined that the average adult actually ingests 2.0 litres per day.
Spring water, a natural resource from which much bottled water comes, is generally imbued with minerals. Tap water, delivered by domestic water systems in developed nations, refers to water piped to homes through a tap. All of these forms of water are commonly drunk, often purified through filtration.
Throughout most of the world, the most common contamination of raw water sources is from human sewage and in particular human faecal pathogens and parasites. In 2006, waterborne diseases were estimated to cause 1.8 million deaths each year while about 1.1 billion people lacked proper drinking water.. It is clear that people in the developing world need to have access to good quality water in sufficient quantity, water purification technology and availability and distribution systems for water. In many parts of the world the only sources of water are from small streams often directly contaminated by sewage.
Most water requires some type of 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 (POU) designs.. 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.
The most reliable way to kill microbial pathogenic agents is to heat water to a rolling boil but this requires abundant sources of fuel and is very onerous on the households, especially where it is difficult to store boiled water in sterile conditions. Other techniques, such as filtration, chemical disinfection, and exposure to ultraviolet radiation (including solar UV) 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.
Over the past decade, an increasing number of field-based studies have been undertaken to determine the success of POU measures in reducing waterborne disease. The ability of POU options to reduce disease is a function of both their ability to remove microbial pathogens if properly applied and such social factors as ease of use and cultural appropriateness. Technologies may generate more (or less) health benefit than their lab-based microbial removal performance would suggest.
The current priority of the proponents of POU treatment is to reach large numbers of low-income households on a sustainable basis. Few POU measures have reached significant scale thus far, but efforts to promote and commercially distribute these products to the world's poor have only been under way for a few years.
Parameters for drinking water quality typically fall under two categories: chemical/physical and microbiological. Chemical/physical parameters include heavy metals, trace organic compounds, total suspended solids (TSS), and turbidity. Microbiological parameters include Coliform bacteria, E. coli, and specific pathogenic species of bacteria (such as cholera-causing Vibrio cholerae), viruses, and protozoan parasites.
Chemical parameters tend to pose more of a chronic health risk through buildup of heavy metals although some components like nitrates/nitrites and arsenic may have a more immediate impact. Physical parameters affect the aesthetics and taste of the drinking water and may complicate the removal of microbial pathogens.
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 (like E. Coli) serves as an indication of contamination by sewage. Additional contaminants include protozoan oocysts such as Cryptosporidium sp., Giardia lamblia, Legionella, and viruses (enteric). Microbial pathogenic parameters are typically of greatest concern because of their immediate health risk.
70% of the Earth's surface is covered by water. Water is available almost everywhere if proper methods are used to get it. Sources where water may be obtained include:
Access to drinkable water is a complicated, yet vital issue. There is great diversity in access not only between countries but within countries and even cities.
Cost is the major limiting factor of access to drinkable water.
The most efficient way to transport and deliver potable water is through pipes. However, this requires a enormous up front infrastructure costs. Further the high continual operating costs mean many systems fall into disrepair in both developed and undeveloped countries. The cost to replace the deteriorating water and sanitation infrastructure of industrialized countries may be as high as $200 billion a year. Further, Leakage of pipes reduces access to water. Leakage rates of 50% are not uncommon in urban systems 
Because of the high initial investments, many debt impoverished nations cannot afford to develop this infrastructure. So people in these areas end up paying a much higher percentage of their income on water.  2003 statistics from El Salvador, for example, indicate that the poorest 20% of households spend more than 10% of their total income on water. In the United Kingdom authorities define spending of more than 3% of one's income on water as a hardship.
The Millennium Development Goal of halving the proportion of people without access to safe drinking water between 1990 and 2015 will probably be reached. Although some countries still face enormous challenges. 
Rural communities are the furthest from meeting the 2015 MDGs drinking water target. Globally only 27% of the rural population has water piped directly to their home and 24% rely on unimproved sources. Of the 884 million people without access to an improved water source, 746 million people (84%) live in rural areas. Sub-Saharan Africa has made the least progress in improved water sources since 1990, improving only 9% to 2006. In contrast, the Eastern Asian region saw a dramatic drop from 45% to 9% reliance on unimproved water in the same time period.
|Peru||80||Philippines||86||South Africa||86||South Korea||92||Sudan||67|
|Note: All industrialized countries (as listed by UNICEF) with data available are at 100%.|
In the U.S, the typical nonconserving single family home uses 69.3 gallons of water per capita per day. In some parts of the country there are water supplies that are dangerously low due to drought, particularly in the West and the South East region of the U.S..
Water is necessary for most life on Earth. Humans can survive for several weeks without food, but for only a few days without water. The exact amount of water a human needs is highly individual, as it depends on the condition of the subject, the amount of physical exercise, and on the environmental temperature and humidity. In the US, the reference daily intake (RDI) for water is 3.7 litres per day for human males older than 18, and 2.7 litres for human females older than 18 including water contained in food, beverages, and drinking water. It is a common misconception that everyone should drink two litres (68 ounces, or about eight 8-oz glasses) of water per day and is not supported by scientific research. Various reviews of all the scientific literature on the topic performed in 2002 and 2008 could not find any solid scientific evidence that recommended drinking eight glasses of water per day.   For example, people in hotter climates will require greater water intake than those in cooler climates. An individual's thirst provides a better guide for how much water they require rather than a specific, fixed number. A more flexible guideline is that a normal person should urinate 4 times per day, and the urine should be a light yellow color.
A constant supply is needed to replenish the fluids lost through normal physiological activities, such as respiration, perspiration and urination. Food contributes 0.5 to 1 litre, and the metabolism of protein, fat, and carbohydrates produces another 0.25 to 0.4 litres, which means that 2 to 3 litres of water for men and 1 to 2 litres of water for women should be taken in as fluid in order to meet the RDI. In terms of mineral nutrients intake, it is unclear what the drinking water contribution is. However, inorganic minerals generally enter surface water and ground water via storm water runoff or through the Earth's crust. Treatment processes also lead to the presence of some mineral nutrients. Examples include fluoride, calcium, zinc, manganese, phosphate, and sodium compounds. Water generated from the biochemical metabolism of nutrients provides a significant proportion of the daily water requirements for some arthropods and desert animals, but provides only a small fraction of a human's necessary intake. There are a variety of trace elements present in virtually all potable water, some of which play a role in metabolism. For example sodium, potassium and chloride are common chemicals found in small quantities in most waters, and these elements play a role (not necessarily major) in body metabolism. Other elements such as fluoride, while beneficial in low concentrations, can cause dental problems and other issues when present at high levels. Water is essential for the growth and maintenance of our bodies, as it is involved in a number of biological processes.
The human kidneys will normally adjust to varying levels of water intake. The kidneys will require time to adjust to the new water intake level. This can cause someone who drinks a lot of water to become dehydrated more easily than someone who routinely drinks less. Survival classes recommend that someone who expects to be in an environment with little water (such as a desert), not to drink water excessively, but rather to drink gradually decreasing amounts for several days before their trip to accustom the kidneys to making concentrated urine. Not using this method can, and has been known to be fatal.
Access to safe drinking water is indicated by the number of people using proper sanitary sources. These improved drinking water sources include household connection, public standpipe, borehole condition, protected dug well, protected spring, and rain water collection. Sources that don't encourage improved drinking water to the same extent as previously mentioned include: unprotected well, unprotected spring, rivers or ponds, vender-provided water, bottled water (consequential of limitations in quantity, not quality of water), and tanker truck water. Access to sanitary water comes hand in hand with access to improved sanitation facilities for excreta. These facilities include connection to public sewer, connection to septic system, pour-flush latrine, and ventilated improved pit latrine. Unimproved sanitation facilities are: public or shared latrine, open pit latrine, or bucket latrine.
Diarrheal diseases cause ninety percent of all deaths of children under five years old in developing countries. Malnutrition, especially protein-energy malnutrition, can decrease the children's resistance to infections, including water-related diarrheal diseases. In 2000-2003, 769,000 children under five years old in sub-Saharan Africa died each year from diarrheal diseases. As a result of only thirty-six percent of the population in the sub-Saharan region having access to proper means of sanitation, more than 2000 childrens' lives are lost every day. In South Asia, 683,000 children under five years old died each year from diarrheal disease from 2000-2003. During the same time period, in developed countries, 700 children under five years old died from diarrheal disease. Improved water supply reduces diarrhea morbidity by twenty-five percent and improvements in drinking water through proper storage in the home and chlorination reduces diarrhea episodes by thirty-nine percent.
Solar water disinfection is a low-cost method of purifying water that can often be implemented with locally available materials. Unlike methods that rely on firewood, it has low impact on the environment.
One program developed to help people gain access to safe drinking water is the Water Aid program. Working in 17 countries to help provide water, Water Aid international is helping the sanitation and hygiene education to some of the world's poorest people.
The Global Framework for Action (GF4A) is a organization that brings together stakeholders, national governments, donors and NGOs (such as Water aid) to define manageable targets and deadlines. 23 Countries are off-track to meet the MDG goals for improved water availability. 
However, not all efforts to increase availability of safe drinking water have been effective, and some have been damaging. The 1980s was declared the International Decade of water by the UN. However, the assumption was made that groundwater is inherently safer than water from rivers, ponds and canals. While instances of cholera, typhoid and diarrhea were reduced toxic level of fluoride were found. Borehole wells were either not tested or not tested thoroughly. Fluoride slowly dissolved from the granite rocks underneath India and slowly poisoned the population, particularly evident in the bone deformations of children. . Further, in Bangladesh, it is estimated that half of the countries 12 million tube wells have unacceptable levels of arsenic due to the wells not being dug deep enough (past 100 M). The Bangladeshi government had spent less than $7 million of the 34 million allocated for solving the problem by the World Bank in 1998.  . Natural arsenic poisoning is a global threat, 140 million people affected in 70 countries on all continents.  These examples illustrate the need to examine each location on a case by case basis and not assume what works in one area will work in another.
In Britain, many schools have poor provision of drinking water to pupils through the day. Studies have been made upon the effect of increasing the provision of water and significant improvements in test scores have been observed. Areas such as Brighton have introduced a Schools Water Policy to ensure an adequate intake of 1.5 to 1.75 litres for 5-10 year olds.
The EU sets legislation on drinking water quality in addition to factors such as how, where and when water can be extracted from the environment. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy, known as the water framework directive, is the primary piece of legislation governing drinking water.
Each member state is responsible for establishing the required policing measures to ensure that the legislation is implemented. For example, in the UK the Drinking Water Inspectorate polices the water companies.
In the United States, the Environmental Protection Agency (EPA) sets standards for tap and public water systems under the Safe Drinking Water Act (SDWA). The Food and Drug Administration (FDA) regulates bottled water as a food product under the Federal Food, Drug, and Cosmetic Act (FFDCA). Bottled water is not necessarily more pure, or more tested, than public tap water. However, there is evidence that the United States federal regulations of drinking water do not ensure safe water, as some of the regulations have not been updated with more recent science. Dr. Peter W. Pruess, who became the head of the U.S. EPA's division analyzing environmental risks in 2004, has been "particularly concerned", and has faced controversy in studies which suggest that regulations against certain chemicals should be tightened.
A standard testing of water's potability consists of drawing a sample from a known property or water source, providing State Certified Nitrate/Nitrogen and Coliform Bacteria Testing, along with E.Coli testing (FHA/VA). It also means providing testing for Total Dissolved Solids, Water Hardness, pH, and Iron Content Testing. A Certified Laboratory must provide proper operation of all Water Softening and Filtration Systems, and provide written results of the above testing with a standarized time frame (2 weeks general).
Drinking water of a variety of qualities is bottled and sold for public consumption throughout the world. Trends in sales and consumption of bottled water have risen significantly in the last two decades in both developed and developing countries.
The qualitative and quantitative aspects of drinking water requirements of domesticated animals are studied and described within the context of animal husbandry. However, relatively few studies have been focused on the drinking behavior of wild animals. A recent study has shown, e.g., that feral pigeons do not discriminate drinking water according to its content of methabolic wastes, such as uric acid or urea (mimicing faeces- or urine-pollution by birds or mammals respectively).