In its document, Guidelines for Safe Recreational Waters Vol 2 – Swimming pools, spas and similar recreational-water environments, chapter 5 – Managing Water and Air Quality (WHO website), the World Health Organization states the following.
“The demand for fast biocidal action – to ensure that an infection of swimmers by transmission of bacteria and viruses via pool water does not occur even when the pool is used in rapid succession by large numbers of bathers – rules out the use of silver or other heavy metals for pool water disinfection, because a long exposure period (several hours) is required for these substances to show a biocidal effect. A quick, sensitive, analytical field procedure for measuring low concentrations of silver is not available.”
The German Federal Environmental Agency stated a very similar conclusion in its press release dated 8 February 2001 (external website). It states (in the final dot point):
“Silver-copper compounds, mentioned by the press as alternatives to chlorination, may not be seriously considered for use in public swimming pools. They take effect too slowly. According to DIN 19643, the disinfectant must reduce the concentration of Pseudomonas aeruginosa by four decimal powers within 30 seconds. Silver-copper compounds take an hour or more for this. What is more, they do not have the necessary disinfectant capacity.”
Published papers in the scientific literature indicate that silver and copper ions require lengthy periods of time (usually in the range of several hours) to exhibit significant anti-bacterial activity. In addition to being slow, the antibacterial activity does not kill all cells but may have only a bacteriostatic effect on a portion of the population.
Virucidal activity also appears to be variable or not present for some viral types. Copper and silver ions in the presence of reduced levels of free chlorine (below 1 ppm) do not ensure the total elimination of viral pathogens from water.