Chemical hazards in drinking-water - hardness

Hardness is considered in the WHO Guidelines for Drinking-water Quality. You can link from here to:

The Guidelines for drinking water quality also consider for individual chemicals:

Rolling revision of the WHO Guidelines for Drinking-water Quality

Hardness is included in the plan of work of the rolling revision of the WHO Guidelines for Drinking-water Quality.

Background

The term hard water is an indication of the presence of usually calcium and magnesium carbonates that reduce the lathering of soaps or precipitate soap residues onto sinks and bathtubs and reduce washing efficiency. These are negative aesthetic and economic effects that can be reduced by either central softening treatment (precipitating calcium and magnesium carbonates) or home water softening (cation exchange replacement of calcium and magnesium with sodium or sometimes potassium using ion exchange resins).

Individuals vary considerably in their needs for and consumption of calcium and magnesium. Available evidence suggests that, because of food habits, many people in most countries fail to obtain from their diets the recommended intakes for one or both of these nutrients. While the concentrations of calcium and magnesium in drinking-water vary markedly from one supply to another, mineral-rich drinking-waters may provide substantial contributions to total intakes of these nutrients for some populations or subgroups. Water treatment processes can affect mineral concentrations, significantly affecting the total intakes of calcium and magnesium for some individuals.

A large number of studies have investigated the potential health effects of drinking-water hardness. Most of these have been ecologic and have found an inverse relationship between water hardness and cardiovascular mortality. Inherent weaknesses in the ecologic study design limit the conclusions that can be drawn from these studies.

Seven case–control studies and two cohort studies of acceptable quality investigating calcium or magnesium and cardiovascular disease or mortality were identified in the literature. Of the case–control studies, one addressed the association between calcium and acute myocardial infarction and three its association with death from cardiovascular disease. Based on identified case–control and cohort studies, the studies show a negative association (i.e. protective effect) between cardiovascular mortality and drinking-water magnesium. The studies indicated that benefits levelled off at a magnesium concentration of about 10 mg/litre. Although this association does not necessarily demonstrate causality, it is consistent with the well known effects of magnesium on cardiovascular function. There does not appear to be an association between drinking-water magnesium and acute myocardial infarction. There is no evidence of an association between hardness or calcium and acute myocardial infarction or deaths from cardiovascular disease (acute myocardial infarction, stroke and hypertension).

Expected end-product(s)

1) Expert Committee report and monograph on health effects of calcium and magnesium in drinking-water, to be published in 2007 and 2008, respectively; 2) background document and summary statement taking into account beneficial effects associated with hardness, to be published in Fourth Edition

Progress to date

A brief discussion paper on water hardness was prepared. The GDWQ WG meeting (Geneva, 2004) agreed that future meetings will further examine the hypotheses concerning the beneficial effects of hardness and determine whether they should be reflected in guidance for hardness or recommended compositions of calcium and magnesium in drinking-water as a contributor to reduced risks of ischaemic cardiovascular disease. The GDWQ WG meeting (Geneva, 2005) agreed that further progress on this issue would await the hardness symposium, held in April 2006. The GDWQ WG meeting (Geneva, 2006) received an update on the conclusions of the hardness symposium and agreed to move forward with a background document on hardness for the Fourth Edition. The GDWQ WG meeting (Berlin, 2007) agreed on a path forward. The GDWQ WG meeting (Singapore, 2008) was informed of a meeting convened by WHO in January 2008 to consider the feasibility of a multi-country study with the goal of elucidating the relationship between hard water (particularly magnesium concentration) and cardiovascular disease mortality.

Other publications of interest