Drinking water: sources, treatment, uses and safety

Human water requirements vary according to physical condition, body mass, activity, ambient temperature, ambient humidity and other factors. Humans consume water in the form of beverages and food, and excrete it in urine, feces, sweat and breath. Water is produced in the body during the oxidative breakdown of organic food substances.

The WHO gives a drinking water requirement estimate of about two litres per day for a 60 kg adult and one litre for a child with a body weight of 10 kg for "high requirement". Recent studies indicate that fluid requirements can also be met by drinking sufficient amounts of juice, milk or coffee and vary greatly from individual to individual.

Tap water is also used for other purposes, such as washing clothes, flushing toilets, cleaning bodies, dishes and apartments. In recent decades, the consumption of drinking water was expected to be between 120 and 140 litres per day and per inhabitant. According to statistics published by the German Association of Energy and Water Industries (BDEW), the per capita consumption of drinking water in Germany has risen to between 120 and 140 litres per day. (BDEW), per capita consumption of drinking water in Germany has fallen continuously since 1990 as a result of the conscious use of water.

In other countries, consumption is sometimes much higher: consumption in Italy is stated at 260 litres per day and inhabitant; the desert city of Dubai consumed 500 litres per day and inhabitant around 2010 and is striving to reduce consumption in the production of drinking water there by desalinating seawater.

In Germany, Austria, Switzerland, France and the Netherlands, drinking water is the most intensively controlled foodstuff and is normally suitable for consumption without any restrictions.

Problems with the quality of drinking water from groundwater can usually be avoided by the proper designation of protected areas. In some cases, however, protection in areas with intensive conventional agricultural use is not sufficient. In particular, excessive slurry fertilisation or old sewage treatment plants and the resulting nitrate input into the groundwater can make the drinking water obtained from them dangerous for infants and young children. In these cases, the water supplier must reduce the nitrate concentration through treatment, deeper wells and cooperation with agriculture.

Water from bank filtrate may contain pollutants from sewage treatment plants or industrial discharges. Pollutants can enter water bodies during "normal operation" or through accidents. Water suppliers on Germany's major rivers have moved to apron control and the provision of redundant techniques for water treatment. Drugs and other pharmacologically active substances, for example X-ray contrast media or sex hormones, can enter drinking water through the water cycle and lead to systemic risks.

In German-speaking countries, drinking water has to meet higher quality standards than industrially packaged mineral water and table water. It is considered to be the best-studied foodstuff. Unlike natural mineral water, drinking water and table water does not have to be "originally pure", i.e. it may be treated and mixed. Thus, drinking water mixed with carbon dioxide - regardless of quality and mineral content - may not be offered as mineral water in restaurants.

In other countries, the quality of drinking water is often worse due to a lack of treatment and monitoring. In popular holiday destinations such as Spain and Portugal, the quality of tap water reportedly varies in some cases from "suitable for drinking" to "hazardous to health if consumed in large quantities". In China, 60 to 80 percent of the groundwater is heavily polluted and no longer suitable for drinking. In Europe, drinking water is generally suitable for cooking.

Pollution

In individual cases, increased contamination of drinking water with pollutants (for example arsenic, lead, cadmium, chloride, iron, copper, nitrate, phosphate, uranium, zinc) can occur at the end consumer. In March 2013, ZDF reported on increased contamination of drinking water with chemical waste such as antibiotics, pesticides or disinfectants. In eastern Switzerland, 300 drinking water and groundwater samples were taken, which showed that the official maximum level of the carcinogenic pesticide chlorothalonil was exceeded in over 10% of the samples. Medicinal substances were also found. Limits are set (in Germany) by the Drinking Water Ordinance, but for many pollutants there are no limits yet.

Lead

Old lead pipes in domestic installations can be responsible for elevated levels of lead in drinking water. In the evaluation of 20,000 drinking water analyses from the period 1994 to 2004, from taps in households, Stiftung Warentest found more than 25 micrograms per litre (µg/l) of lead in five percent of the samples. According to the study, there was an increased risk in eastern German regions, in Schleswig-Holstein and in the greater Hamburg, Bremen, Bonn and Frankfurt areas. The limit value according to TrinkwV is 10 µg/l. Drinking water analyses can clarify whether one's own domestic installation is affected.

As of 2021, up to 20 million people in the U.S. are supplied with water from lead pipes.

Arsenic and fluoride

Around 300 million people worldwide obtain their water from groundwater supplies. However, around 10 per cent of groundwater wells are contaminated with arsenic or fluoride. These trace substances are mostly of natural origin and are washed out by water from rocks and sediments. In 2008, the Swiss Federal Institute of Aquatic Science and Technology (Eawag) presented a new method for the production of hazard maps for geogenic toxicants in groundwater, without the need to examine all the wells and groundwater supplies in a region.

In 2016, Eawag made its knowledge freely available on the Groundwater Assessment Platform (GAP). This Internet portal enables members of the authorities, NGO staff and other experts to upload their own measurement data and produce risk maps for areas of their choice.

Uranium exposure

Germany

In 2008, the consumer organisation Foodwatch warned of high uranium concentrations, with 39 µg/l uranium detected in Maroldsweisach in the district of Hassberge (Bavaria), 33 µg/l in Lobenrot in the district of Esslingen and 30.08 µg/l in Reimershagen in the district of Rostock (Mecklenburg-Western Pomerania). A total of 8200 reported measurements show 150 above 10 µg/l, the limit value of the amended Drinking Water Ordinance of 2011. On average, drinking water in Germany contains less uranium (0.3 µg/l) than mineral water (2.8 µg/l). The connection between elevated uranium levels in mineral and drinking waters and the geology of the groundwater reservoir rocks was investigated nationwide for the first time in 2008. It was found that elevated uranium levels are linked to formations such as red sandstone or Keuper, which themselves have elevated uranium levels geogenically. Locally, uranium from phosphate fertilizers has leached into the groundwater.

Switzerland

As part of a monitoring programme by the Federal Office of Public Health (FOPH) in the 2000s, the uranium content of drinking water was investigated on the basis of 5000 samples in Switzerland. The results were scientifically analysed. It was found that higher concentrations were found above all in the Alpine region if the water was obtained from groundwater or spring water "in contact with uranium-bearing rocks and sediments." In 0.3% of the samples, the WHO guideline value of 30 µg/l was exceeded. Based on the test results, the FOPH intends to stipulate the limit value of 30 µg/l in the Ordinance on Foreign Substances and Ingredients, which would mean that "affected municipalities would have to remediate their water supplies within a transitional period of 5 years."

Biological stresses

Drinking water can in individual cases be the source of epidemic disease outbreaks caused by enteric pathogenic viruses. In Finland, for example, a study of drinking water-related norovirus outbreaks was carried out between 1998 and 2003. In 10 of 18 Norwalk virus outbreaks, the detected subtypes were found in the stool samples of the patients as in the corresponding drinking water samples. These are exceptions, which occur regionally in a very limited manner and which are immediately eliminated by remediation. According to the Federal Health Office and the Federal Environment Agency, well over 99 % of the drinking water supplied in Germany is free of objections.