Nutrient minerals in drinking-water and the potential health consequences of consumption of demineralized and remineralized and altered mineral content drinking-water: Consensus of the meeting
Desalination of sea and brackish water is widely practiced and rapidly growing as the principal source of new fresh water in the world. Water treatment processes including desalination followed by remineralization alter the mineral composition of drinking water compared to water derived from many conventional fresh water sources. The WHO Guidelines for Drinking-water Quality (GDWQ) provide a point of reference for drinking water quality regulations and standards setting world-wide. The Guidelines are kept up-to-date through a process of ‘rolling revision’ which include the development of accompanying documents substantiating the contents of the guidelines and providing guidance on experience with good practice in achieving safe drinking-water. This plan of work includes the development of guidance on good practices of desalination as a source of safe drinking water.
To examine the nutritional aspects of water consumption as part of the process for guidance development, WHO assembled a group of nutrition, medical and scientific experts on November 11-13, 2003 in Rome, Italy at the WHO European Centre for Environment and Health. The meeting was attended by 18 technical participants from Canada, Chile, Czech Republic, Germany, Ireland, Italy, Moldova, Singapore, Sweden, UK and USA. The task was to examine the potential health consequences of long term consumption of water that has been ‘manufactured or modified’ to add or delete minerals and thus may have altered mineral content.
We wish to express our appreciation and gratefully acknowledge the organizations that provided financial and other support for the meeting. These included the International Life Sciences Institute (ILSI); the U.S. Environmental Protection Agency Offices of Ground Water and Drinking Water (Washington, D.C.), and Research and Development (Research Triangle Park, North Carolina); the American Water Works Association Research Foundation; the Center for Human Nutrition, University of Nebraska Medical Center, Omaha, Nebraska USA; and Health Canada, Water Quality and Health Bureau, Ottawa, Ontario Canada. WHO, Water Sanitation and Health, Geneva. WHO European Regional Office, Rome. WHO, EMRO, Cairo.
Expert Committee Members: Roger Aertgeerts, Rebecca Calderon, Gerald Combs, Joseph Cotruvo, Gunther Craun, Jan Ekstrand, Floyd Frost, John Fawell, Ann Grandjean, Suzanne Harris, Frantizek Kozisek, Michael Lennon, Silvano Monarca, Denis O’Mullane, Manuel Olivares, Choon Nam Ong, Souleh Semalulu, Ion Shalaru, Erika Sievers. Contributors: Charles Abernathy, Kunal Bagchi, Jamie Bartram, Leslie Klevay, F. Donato, Joyce Donohue, George Hallberg, Peter Lassovszky, Curtis Morris, Ricardo Uauy, Helen Whelton, I. Zerbini.
In 1999, WHO’s Eastern Mediterranean Regional Office had initiated a proposal to develop Guidance on desalination because numerous existing facilities had developed on a case-by-case basis with potentially inconsistent consideration of important principles of siting, coastal zone protection, chemicals and contact surfaces used in plant operation, water treatment and plant construction , contaminants, water distribution, microbial control and final product water quality. International consensus guidance would reduce ad hoc decision making, facilitate informed decision making and thus reduce costs and allow more rapid project completion. Such guidance would be timely given the rapidly-increasing application of desalination world-wide. In 2000, the proposal to proceed was endorsed at a WHO Guidelines on Drinking-water Quality Committee meeting in Berlin, Germany. In May 2001, the proposal was examined at a dedicated expert consultation in Manama, Bahrain and an operating plan and program were proposed.
This Expert Meeting addressed several health considerations potentially arising from long-term consumption of water derived from water that has undergone major alteration in its mineral content, such that it must be remineralized to be compatibile with piped distribution systems. It examined the relationship between calcium and magnesium in drinking water on certain cardiovascular disease risks, and also health consequences of consumption of fluoride in drinking water.
Drinking water, regardless of its source, is usually subjected to one or more of a variety of treatment processes aimed at improving its safety and/or aesthetic quality. These processes are selected according to the source water and the constituents and contaminants that require removal. Surface fresh waters will often undergo coagulation, sedimentation, rapid sand filtration and disinfection. Ground waters, which are often naturally filtered, usually undergo less treatment which could be limited to disinfection alone. Additional treatment processes could include pH adjustment, softening, corrosion control chemicals addition, alkalinity adjustment, carbon filtration/adsorption, membrane filtration, slow sand filtration and supplemental fluoridation. The disinfectants applied could include chlorine, chlorine dioxide, ozone, or chloramines. Some substances will be added by the chemicals used for treatment i.e. direct and indirect additives.
For waters with high salinity (e.g. up to ~ 40,000 ppm) such as sea water or brackish waters, treatment processes must remove most of the dissolved salts in order to make the water potable. The major methods include reverse osmosis, membrane treatments or several distillation/vapor condensation processes. These processes require extensive pretreatment and water conditioning, and subsequent remineralization so that the finished water which is now significantly different from the source water will not be overly aggressive to the piped distribution systems that it will pass through on the way to consumers. In the course of water treatment, contaminants and some potentially beneficial nutrients will be removed and some might be added. Other waters, although not deliberately demineralized may also undergo significant changes in their mineral content due to the treatment processes.
Remineralization and increased alkalinity for stabilization of the water are often accomplished by use of lime or limestone. Caustic soda, bicarbonate, sodium carbonate, phosphates, and silicates are sometimes used alone or in combination. The mineral composition of limestone is highly variable depending upon the quarry location and it is usually predominantly calcium carbonate, but often contains significant amounts of magnesium carbonate along with numerous other minerals. Quality specifications exist for chemicals and materials used in the treatment of drinking water. These specifications are intended to assure that drinking water treatment grade chemicals will be used and that their addition will not inadvertently contribute significant levels of potentially harmful contaminants to the finished drinking water under typical use conditions.
Charge to the Expert Group
The group was asked to examine several issues relating to the composition of drinking water that has undergone significant treatment relevant to drinking water guidelines aimed at protecting and enhancing public health:
- What is the potential contribution of drinking water to total nutrition?
- What are the drinking water intake requirements for individuals considering climate, exercise, age etc.?
- Which substances are often found in drinking water that can contribute significantly to health and well-being?
- Under what conditions can drinking water be a significant contribution to the total dietary intake of certain beneficial substances?
- What conclusions can be drawn on the relationship between calcium, magnesium, and other trace elements in water and mortality from certain types of cardiovascular disease?
- For which substances, if any, can a case be made for supplementation of mineral content in treated drinking water from the public health perspective?
- What is the role of fluoride in drinking water with respect to dental benefits and dental fluorosis, and skeletal fluorosis?