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Friday, November 21, 2008

Drinking water

Drinking water is water that is of sufficiently high quality that it can be drunk without risk of immediate or long term harm. Such water is commonly called potable water. 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 drunk or used in food preparation.

Over large parts of the world, humans drink water that contains disease vectors or pathogens or contain unacceptable levels of dissolved contaminants or solids in suspension. Such waters are not potable water and drinking such waters or using them in cooking leads to widespread acute and chronic illness and is a major cause of death in many 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.

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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, 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. However, even where wells are used this does not eliminate the risk of contamination .

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.

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 varying forms of 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.

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 lambia, Legionella, and viruses (enteric). Microbial pathogenic parameters are typically of greatest concern because of their immediate health risk.

Access to drinking water

Only forty-six percent of people in Africa have safe drinking water.
Drinking water vending machines in Thailand. One litre of purified water is sold (into the customer's own bottle) for 1 baht

Earth's surface consists of 70% water. Water is available almost everywhere if proper methods are used to get it. Sources where water may be obtained include:

* ground sources such as groundwater, hyporheic zones and aquifers.
* precipitation which includes rain, hail, snow, fog, etc.
* surface water such as rivers, streams, glaciers
* biological sources such as plants.
* the sea through de-salination

As a country’s economy becomes richer, a larger percentage of its people tend to have access to drinking water and sanitation. Access to drinking water is measured by the number of people who have a reasonable means of getting an adequate amount of water that is safe for drinking, washing, and essential household activities.

As of the year 2006 (and pre-existing for at least three decades), there is a substantial shortfall in availability of potable water in less developed countries, principally because of migration from the countryside to urban areas in countries with low average rainfall and limited infrastructure. As of the year 2000, 27 percent of the populations of lesser developed countries did not have access to safe drinking water[6]. Implications for disease propagation are significant. Many nations have water quality regulations for water sold as drinking water, although these are often not strictly enforced outside of the developed world. The World Health Organization sets international standards for drinking water. A broad classification of drinking water safety worldwide can be found in Safe Water for International Travellers.

It reflects the health of a country’s people and the country’s capacity to collect, clean, and distribute water to consumers. According to the United Nations' World Health Organization (WHO) more than one billion people in low and middle-income countries lack access to safe water for drinking, personal hygiene and domestic use. These numbers represent more than 20 percent of the world’s people. In addition, close to 3 billion people did not have access to adequate sanitation facilities. (For details see data on the website of the Joint Monitoring Programme (JMP) on water and sanitation of WHO and UNICEF.)

While the occurrence of waterborne diseases in developed countries is generally low due to a generally good system of water treatment, distribution and monitoring, waterborne diseases are among the leading causes of morbidity and mortality in low- and middle-income countries, frequently called developing countries.

The main reason for poor access to safe water is the inability to finance and to adequately maintain the necessary infrastructure. Overpopulation and scarcity of water resources are contributing factors.

Many other countries also lack in the amount of safe drinking water that they need to survive. Some of the countries have less than twenty percent of the population that has access to safe drinking water. For example in Africa, with more than 700 million people, only forty-six percent of people have safe drinking water. The more populous Asia Pacific region with over three billion people, eighty percent of whom with access to drinking water, still leaves over 600 million people without access to safe drinking water.

The lack of water and the lack of hygiene is one of the biggest problems that many poor countries have encountered in progressing their way of living. The problem has reached such endemic proportions that 2.2 million deaths per annum occur from unsanitary water - ninety percent of these are children under the age of five. 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 is useful in helping the sanitation and hygiene education to some of the world's poorest people. 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.

In the US, the typical nonconserving single family home uses 69.3 gallons of water per capita per day. These figures are concerning in some parts of the country where water supplies are dangerously low due to drought, particularly in the West and the South East region of the U.S .

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