Drinking water, also known as potable water, is water that is safe to drink or use for food preparation. The amount of drinking water required to maintain good health varies, and depends on physical activity level, age, health-related issues, and environmental conditions.[1] On average, people in the United States generally drink one litre of water per day and 95% drink less than three litres per day.[2] For those who work in a hot climate, up to 16 litres a day may be required.
Typically in developed countries, tap water meets drinking water quality standards, even though only a small proportion is actually consumed or used in food preparation. Other typical uses include washing, toilets, and irrigation. Greywater may also be used for toilets or irrigation. Its use for irrigation however may be associated with risks.[3] Water may also be unacceptable due to levels of toxins or suspended solids.
Globally, by 2015, 89% of people had access to water from a source that is suitable for drinking – called improved water source.[3] In Sub-Saharan Africa, access to potable water ranged from 40% to 80% of the population. Nearly 4.2 billion people worldwide had access to tap water, while another 2.4 billion had access to wells or public taps.[3] The World Health Organization considers access to safe drinking-water a basic human right.
About 1 to 2 billion people lack safe drinking water,[4] a problem that causes 30,000 deaths each week.[5] More people die from unsafe water than from war, U.N. Secretary-General Ban Ki-Moon said in 2010.
Water quality
EPA drinking water security poster from 2003
Parameters for drinking water quality typically fall within three categories:
physical
chemical
microbiological
Physical and chemical 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 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.
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).[67] Microbial pathogenic parameters are typically of greatest concern because of their immediate health risk.
Throughout most of the world, the most common contamination of raw water sources is from human sewage in particular human faecal pathogens and parasites. In 2006, waterborne diseases were estimated to cause 1.8 million deaths while about 1.1 billion people lacked proper drinking water.[68] In parts of the world, the only sources of water are from small streams that are often directly contaminated by sewage.
There is increasing concern over the health effects of engineered nanoparticles (ENPs) released into the natural environment. One potential indirect exposure route is through the consumption of contaminated drinking waters. To address these concerns, the U.K. Drinking Water Inspectorate (DWI) has published a "Review of the risks posed to drinking water by man-made nanoparticles" (DWI 70/2/246). The study, which was funded by the Department for Food and Rural Affairs (Defra), was undertaken by the Food and Environment Research Agency (Fera) in collaboration with a multi-disciplinary team of experts including scientists from the Institute of Occupational Medicine/SAFENANO. The study explored the potential for ENPs to contaminate drinking water supplies and to establish the significance of the drinking water exposure route compared to other routes of exposure.
Test have found 83% of 159 water samples from around the world were contaminated with plastic fibers.
Greenpeace reported that in 2005 more than half the surface rivers in eight provinces of China were unsuitable for human contact.
Improved water sources
Access to safe drinking water is indicated by safe water sources. These improved drinking water sources include household connection, public standpipe, borehole condition, protected dug well, protected spring, and rain water collection. Sources that do not encourage improved drinking water to the same extent as previously mentioned include: unprotected wells, unprotected springs, 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, such as connection to public sewer, connection to septic system, or a pit latrine with a slab or water seal.
Water treatment
Water treatment plant 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 (POU) designs.[73] 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[75] 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 (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,[76] 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.
Point of use methods
The ability of point of use (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.
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.