Water - a conveyor of disease or health benefits?
Desalination is considered by some as the answer to Britain's water shortage. However, what implications could low mineral content water have on the public's health. Dr Ian Pallett reports.The gradual increase in the use of desalination to provide water for municipal supplies has raised concerns regarding potential health impacts of drinking water supplies with a low mineral content. In particular, the Eastern Mediterranean Regional Office (EMRO) of the World Health Organisation (WHO) became concerned and requested advice on the subject from the WHO headquarters.
The WHO arranged a workshop for invited experts in Rome in 2003, which considered expert reviews on health-related issues concerning use of desalinated water for drinking and cooking. The group was to assemble all the relevant information on desalination techniques, which was transposed into demineralisation, and their use to provide municipal water supplies.
They also reviewed all health consequences that could be linked to consumption of low mineral content water. The papers and the workshop review were made available for public consultation prior to being published by WHO 2005.
The health considerations concentrated mainly on the relevance of calcium and magnesium in drinking water and especially the long-running debate on whether these minerals in drinking water exerted an influence on the incidence of cardiovascular disease (CVD).
This inevitably drew the supply of naturally soft water into the discussions as the studies were epidemiological investigations into comparing the incidence of CVD in
naturally soft, rather than treated softened, water and naturally hard water supplies.
If hardness minerals did reduce the incidence of CVD then an argument could be advanced that naturally soft waters should be hardened before distribution in municipal supplies - a significant concern for water quality regulators and suppliers.
Due to the potential impact of the outcome for water supplies and in the search for a better understanding of the issues the WHO arranged an international symposium - Health Aspects of Calcium and Magnesium in Drinking Water - last April in Baltimore. It was followed by a workshop for invited experts to peer review the information and to produce a consensus report that would facilitate the preparation of a defined WHO policy concerning minerals in drinking water.
The consensus report is still to be published.
The symposium heard from a wide range of experts in human health and nutrition - they presented and reviewed data demonstrating the importance of calcium and magnesium to health and well being. It was reported that once past adolescence people became increasingly deficient in both calcium and magnesium in both developing and developed countries.
As would be expected, general diet (food rather than water) was important as a source of calcium, especially dairy products. In developing countries the diet and water supply was often deficient in quality and quantity and so water borne minerals may be more likely to have an influence.
This was not the case in developed countries, although dietary selection could be influential and the quality (mineral content) of the water supply may be relevant. These discussions also highlighted the uncertainty over the values of recommended daily allowances for nutrients, including minerals, leading to the extent of the mineral deficiencies being questioned by some experts.
One concern from the Rome meeting was the incompleteness of the review of publications and the absence of an assessment of the quality of the large number of publications drawing conclusions from epidemiological studies, which can be difficult to conduct and interpret.
The UK Drinking Water Inspectorate commissioned a formal systematic Review of Evidence For Relationship Between Incidence of Cardiovascular Disease and Water Hardness. Prof. Paul Hunter, from the University of East Anglia, oversaw the review and prepared a report*, saying that in his opinion there was probably not a relationship between water hardness and calcium with CVD mortality while there probably was such a relationship between magnesium and CVD mortality.
It is important to note that Prof Hunter's conclusions relate to CVD mortality not incidence of non-fatal CVD. Dr Morris, of the University College in London, reported that the British Regional Heart Study - begun in the 1970s - had not found a link between calcium or magnesium in water and CVD.
It will be interesting to see if the report from the expert meeting following the Baltimore symposium draws any conclusions regarding water hardness, calcium or magnesium and the incidence of CVD.
It is this information which could have a significant impact on the revision of WHO Guidelines on Drinking Water Quality which are expected to be published as the fourth edition in 2008 on the fiftieth anniversary of the publication of the first edition.
In his keynote address opening the Baltimore Symposium, Jamie Bartram, coordinator, Water, Sanitation and Health, at WHO, reviewed the progress with the development of water supplies, treatment and human attitudes to water.
The necessity for water was unquestioned but natural water bodies have long been used as sources of supply as well as repositories for waste.
As regards water supply, during the nineteenth century water was generally seen as potentially a carrier of disease and so treatments were introduced and care with consumption was needed. During the twentieth century treated municipal water supplies were generally seen as safe sources of water.
However, since the end of the last century, the perception that water could be a purveyor of health benefits has begun to develop. Fluoridation is a credible example of this, and lifestyle claims for some bottled waters are increasingly being made.
It may be that the absence of hardness minerals is beneficial to health. A clinical trial is to take place from 2007 to 2009 which will investigate whether there is a benefit to eczema sufferers from using ion- exchange softened water. In 1998 a paper in the Lancet presented epidemiological evidence linking a rise in childhood eczema with increasing water hardness.
The clinical trial will evaluate the strength of the link and so will assess the
evidence as to whether there is a health benefit for a significant number of people from the absence rather than presence of water hardness.
The conclusions from the Baltimore meeting are expected to be influential on regulations regarding the mineral content of water supplies. The outcome will be of personal interest for many because of potential health implications. It will also be likely to have a significant impact on the water supply industry and its equipment and process supply chain.
The application of established and new water treatment process technologies may need to be reviewed and modified if the experts conclude there are health consequences and benefits from the presence of water hardness or calcium or magnesium. Regulators will also perceive such conclusions as requiring support by
Dr Ian Pallett is British Water's technical director.
T: 0207 957 4554.
* The Review of Evidence For Relationship Between Incidence of Cardiovascular Disease and Water Hardness is available at www.dwi.gov.uk/research/research.shtm