Classification of mineral water types and comparison with drinking water standards

Abstract

In a study of 291 mineral waters from 41 different countries, 9–20% exceeded the Dutch drinking water standards for chloride, calcium, magnesium, potassium, sodium, sulphate, and fluorine. The mineral water quality cannot be qualified as bad because the standards for these compounds (with the exception of fluorine) are not based on health issues, but matters regarding undesirable taste and possible adverse effects on the water supply system. For the mineral water data set, the amount of dissolved compounds, hardness, and chloride content appear to be the most distinctive criteria. A mineral water type classification based on these criteria will offer consumers a tool for assessing mineral water on the basis of the chemical composition data on the bottle label. In terms of the criteria mentioned, average Dutch tap water strongly resembles the Belgian and Dutch mineral waters. This similarity does not extend to the price, since Dutch tap water is about 500 times cheaper.

Appendix A

Drinking water standards

According to the WHO (1993), no standards have been established for TDS, chloride, sodium, potassium, hardness, and sulphate and their effects on health. The only standards that have been established are based on taste. Moreover, an increased concentration of these compounds will often lead to corrosion of water pipes or to scale deposits. The nitrate standard, however, is based on health effects. This also applies to the fluorine standard, but it is mentioned that depending on local climatological conditions, and the amount of water consumed, it is sometimes difficult to meet this standard. The chloride standard is primarily based on the undesirable taste effect at a concentration higher than about 250 mg/l. However, people may get used to drinking water with a chloride concentration higher than 250 mg/l, and a concentration up to 600 mg/l is considered safe. A very high chloride concentration, however, leads to an increased risk of corrosion of the metals in the distribution system, which is also related to the hardness of the water. This may result in an increased concentration of metals in the drinking water. Regarding sodium, it is believed that there is a relationship between sodium levels in drinking water and the occurrence of high blood pressure, however, no firm evidence supports this. Therefore, the sodium standard is only based on negative taste effects. These occur at a concentration higher than 200 mg/l. No data are available on the possible health effects of the TDS content. However, TDS may strongly influence the taste of drinking water. Water with a TDS lower than 1,000 mg/l is usually acceptable for consumers, although this may strongly depend on local conditions. A higher TDS may lead to extreme scale deposits in pipelines, boilers, and home appliances. Water with a low TDS tastes flat and is often considered to be tasteless. There are indications that extremely soft water adversely affects the mineral balance. However, no detailed studies are available for evaluation. The public acceptance of the hardness of the water strongly depends on the local conditions. The taste limit for calcium is somewhere in between 100–300 mg/l and for magnesium it is probably lower. In some cases, a hardness of 500 mg/l is tolerated by consumers. Depending on factors such as pH and alkalinity, a hardness of more than about 200 mg/l will lead to scale deposits in the piping system. On the other hand, soft water, with a hardness of less than 100 mg/l, may cause corrosion in the piping system. Sulphate is one of the least toxic anions. However, the presence of a high concentration in the drinking water may lead to dehydration, stomach complaints, and possibly diarrhea. Therefore, authorities are advised to be alert in cases of occurrence of water with a sulphate concentration higher than 500 mg/l. Moreover, sulphate has a clear taste effect, which varies between 250 mg/l for sodium sulphate and 1,000 mg/l for calcium sulphate. In general, the adverse affect on the taste is said to be minimal at levels lower than 250 mg/l. The 50 mg/l standard for nitrate is based on health effects. The WHO standard for fluorine of 1.5 mg/l is also based on health effects. A higher concentration increases the chance of skeletal deformations (fluorosis).