Water Quality Standards

Silver occurs naturally mainly in the form of its very insoluble and immobile oxides, sulfides, and some salts. It has occasionally been found in ground, surface, and drinking-water at concentrations above 5 µg/litre. Levels in drinking-water treated with silver for disinfection (see Protection and improvement of water quality) may be above 50 µg/litre. Recent estimates of daily intake are about 7 µg per person.

Only a small percentage of silver is absorbed. Retention rates in humans and laboratory animals range between 0 and 10%.

The only obvious sign of silver overload is argyria, a condition in which skin and hair are heavily discoloured by silver in the tissues. An oral NOAEL for argyria in humans for a total lifetime intake of 10 g of silver was estimated on the basis of human case reports and long-term animal experiments.

The low levels of silver in drinking-water, generally below 5 µg/litre, are not relevant to human health with respect to argyria. On the other hand, special situations exist where silver salts may be used to maintain the bacteriological quality of drinking-water. Higher levels of silver, up to 0.1 mg/litre (this concentration gives a total dose over 70 years of half the human NOAEL of 10 g), could be tolerated in such cases without risk to health.

No health-based guideline value is proposed for silver in drinking-water.