Drinking water or potable water is water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm. In most developed countries The term developed country is used to describe countries that have a high level of development according to some criteria. Which criteria, and which countries are classified as being developed, is a contentious issue and is surrounded by fierce debate. Economic criteria have tended to dominate discussions. One such criterion is income per capita;, 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 In epidemiology, a vector is an insect or any living carrier that transmits an infectious agent.[page needed] Vectors are vehicles by which infections are transmitted from one host to another. Most commonly known vectors consist of arthropods, domestic animals, or mammals that assist in transmitting parasitic organisms to humans or other mammals, pathogens A pathogen, (from Greek πάθος pathos "suffering, passion", and γἰγνομαι gignomai (gen-) "I give birth to") an infectious agent, or more commonly germ, is a biological agent that causes disease to its host. There are several substrates and pathways whereby pathogens can invade a host; the principal pathways have 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 Waterborne diseases are caused by pathogenic microorganisms which are directly transmitted when contaminated fresh water is consumed. Contaminated fresh water, used in the preparation of food, can be the source of foodborne disease through consumption of the same microorganisms. According to the World Health Organization, diarrheal disease is a major public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals." It is concerned with threats to the overall health of a community based on population health analysis. The goal in developing countries.

Typically, water supply networks A water supply system or water supply network is a system of engineered hydrologic and hydraulic components which provide water supply. A water supply system typically includes: deliver potable water, whether it is to be used for drinking, washing or landscape Landscape comprises the visible features of an area of land, including the physical elements of landforms, water bodies such as rivers, lakes and the sea, living elements of land cover including indigenous vegetation, human elements including land uses, buildings and structures, and transitory elements such as lighting and weather conditions irrigation Irrigation is an artificial application of water to the soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall. Additionally, irrigation also has a few other uses in crop production, which include protecting plants. One counterexample is urban China China is seen variously as an ancient civilization extending over a large area in East Asia, a nation and/or a multinational entity, where drinking water can optionally be delivered by a separate tap.

General

Water has always been an important and life-sustaining drink to humans and is essential to the survival of all organisms^[1]. Excluding fat Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Although the words "oils", "fats",, water composes approximately 70% of the human body The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs. By the time the human reaches adulthood, the body consists of close to 50 trillion cells, the basic unit of life. These cells are organised biologically to eventually form the whole body by mass. It is a crucial component of metabolic Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular processes and serves as a solvent A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature. Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as a paint thinner (e.g. toluene, turpentine), as nail polish removers and for many bodily solutes In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. 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 The litre is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case (l and L). The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau. Although the litre is not an SI unit, it is accepted for use with the SI, and has appeared in several),^[2][3] and the British Dietetic Association The British Dietetic Association is a professional association and trade union for dieticians in the United Kingdom. It was founded in 1936 and is affiliated to the Trades Union Congress and the Scottish Trades Union Congress recommends 1.8 litres.^[1] The United States Environmental Protection Agency The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to protect human health and the environment, by writing and enforcing regulations based on laws passed by Congress. The EPA was proposed by President Richard Nixon and began operation on December 2, 1970, when its establishment was passed in risk assessment calculations assumes that the average American adult ingests 2.0 litres per day.^[3]

Water quality and contaminants

Throughout most of the world, the most common contamination of raw water sources is from human sewage Sewage is water-carried wastes, in either solution or suspension, that is intended to flow away from a community. Also known as wastewater flows, sewage is the used water supply of the community. It is more than 99.9% pure water and is characterized by its volume or rate of flow, its physical condition, its chemical constituents, and the and in particular human faecal pathogens and parasites. In 2006, waterborne diseases Waterborne diseases are caused by pathogenic microorganisms which are directly transmitted when contaminated fresh water is consumed. Contaminated fresh water, used in the preparation of food, can be the source of foodborne disease through consumption of the same microorganisms. According to the World Health Organization, diarrheal disease were estimated to cause 1.8 million deaths each year while about 1.1 billion people lacked proper drinking water.^[4] It is clear that people in the developing world need to have access to good quality water in sufficient quantity, water purification Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from raw water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption but water purification may also be designed for a variety of other purposes, including meeting the requirements of medical, 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 Water treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the concentration of such contaminants so the water include both community-scale and household-scale point-of-use (POU) designs.^[5] A few large urban areas such as Christchurch Christchurch is the largest city in the South Island of New Zealand, and the country's second-largest urban area. It lies one third of the way down the South Island's east coast, just north of Banks Peninsula which itself, since 2006, lies within the formal limits of Christchurch, New Zealand New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori language name for New Zealand is Aotearoa, commonly translated as The Land of the Long White Cloud. The Realm of New Zealand also have access to sufficiently pure water of sufficient volume that no treatment of the raw water is required.^[6]

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.

In emergency situations when conventional treatment systems have been compromised, water borne pathogens may be killed or inactivated by boiling Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. Thus, a liquid may also boil when the pressure of the^[7] 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 and is not a reliable way to kill some encysted parasites such as Cryptosporidium or the bacterium Clostridium. 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,^[8] but these suffer from the same problems as boiling methods.

Parameters for drinking water quality typically fall under two categories: chemical/physical and microbiological. Chemical/physical parameters include heavy metals A heavy metal is a member of an ill-defined subset of elements that exhibit metallic properties, which would mainly include the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight, and some on chemical properties or toxicity, trace organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The distinction between "organic" and ", total suspended solids Total suspended solids is a water quality measurement usually abbreviated TSS. It is listed as a conventional pollutant in the U.S. Clean Water Act. This parameter was at one time called non-filterable residue , a term that refers to the identical measurement: the dry-weight of particles trapped by a filter, typically of a specified pore size (TSS), and turbidity Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Microbiological parameters include Coliform bacteria Coliform is the name of a test adopted in 1914 by the Public Health Service for the Enterobacteriaceae family. It is the commonly-used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming organisms. Some enteron forms can ferment lactose with the production of acid and gas when, E. coli Escherichia coli is a Gram negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for product recalls. The harmless strains are part of the, and specific pathogenic species of bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, (such as cholera Cholera is a severe infection caused by the bacterium Vibrio cholerae, which primarily affects the small intestine. The main symptoms include profuse watery diarrhea and vomiting. Transmission is primarily by the acquisition of the pathogen through contaminated drinking water or infected food. The severity of the diarrhea and associated vomiting-causing Vibrio cholerae Vibrio cholerae is a gram negative comma shaped bacterium with a polar flagellum that causes cholera in humans. V. cholerae and other species of the genus Vibrio belong to the gamma subdivision of the Proteobacteria. There are two major biotypes of V. cholerae, classical and El Tor, and numerous other serogroups), viruses A virus is a small infectious agent that can replicate only inside the living cells of organisms. Most viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,, and protozoan Protozoa is a subkingdom of microorganisms that are classified generally as unicellular non-fungal eukaryotes. Protozoans are a major component of the ecosystem parasites Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the host.

Chemical parameters tend to pose more of a chronic health risk through buildup of heavy metals although some components like nitrates/nitrites and arsenic Arsenic is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92. Arsenic was first documented by Albertus Magnus in 1250. Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow (molecular non-metallic) and several black and grey forms (metalloids). Three metalloidal forms of 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 Coliform is the name of a test adopted in 1914 by the Public Health Service for the Enterobacteriaceae family. It is the commonly-used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming organisms. Some enteron forms can ferment lactose with the production of acid and gas when, a convenient marker for a class of harmful fecal Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus (or cloaca) during defecation pathogens A pathogen, (from Greek πάθος pathos "suffering, passion", and γἰγνομαι gignomai (gen-) "I give birth to") an infectious agent, or more commonly germ, is a biological agent that causes disease to its host. There are several substrates and pathways whereby pathogens can invade a host; the principal pathways have. The presence of fecal coliforms Fecal coliform is the name of a test developed by the Dutch physician Christiaan Eijkman for coli bacilli. They are facultatively-anaerobic, rod-shaped, gram-negative, non-sporulating bacteria. They are capable of growth in the presence of bile salts or similar surface agents, oxidase negative, and produce acid and gas from lactose within 48 hours (like E. Coli Escherichia coli is a Gram negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for product recalls. The harmless strains are part of the) serves as an indication of contamination by sewage Sewage is water-carried wastes, in either solution or suspension, that is intended to flow away from a community. Also known as wastewater flows, sewage is the used water supply of the community. It is more than 99.9% pure water and is characterized by its volume or rate of flow, its physical condition, its chemical constituents, and the. Additional contaminants include protozoan Protozoa is a subkingdom of microorganisms that are classified generally as unicellular non-fungal eukaryotes. Protozoans are a major component of the ecosystem oocysts such as Cryptosporidium Cryptosporidiosis, also known as crypto, is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection. It is spread through the fecal-oral route, often through contaminated water; the main symptom is self-limiting diarrhea in sp., Giardia lamblia, Legionella, and viruses (enteric).^[9] Microbial pathogenic parameters are typically of greatest concern because of their immediate health risk.

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