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VOLUME VI, Number 11, May 1975


Scores of independent tests by many methods in six countries have shown that silver promptly kills bacteria in water and maintains water purity over long periods of time. For swimming pools, silver in filters keeps water crystal clear as well as clean, without the usual disinfectants that sting and bleach. It adds to the joy of swimming.

The most dramatic purification tests occurred last month in a 20,000-gallon swimming pool in Nebraska. There was no disinfectant of any kind in the water. Fifty gallons of municipal sewage plant effluent were put into the pool. That produced a dangerous concentration of 7,000 E. coli cells per 100 millilitres (half a cup) of water. Contents of the pool then were pumped through a tank containing alternating anodic and cathodic silver electrodes for disinfection. Within three hours the pool was entirely free of E. coli and the water, analyzed by the atomic absorption process, contained only 3.2 parts of silver per billion parts of water.

To determine the enduring efficiency of silver purification, the Allegheny County Health Department in Pennsylvania conducted tests in a 152,000-gallon pool which previously had been disinfected by a 50-pounds-per-day gas chlorinator. That system was replaced by a silver system for the swimming seasons in 1974 and 1975. Pool water circulated through a filter of activated carbon impregnated with metallic silver. As a supplement, three pounds of calcium hypochlorite were put into the water each night to oxidize organic matter introduced into the pool by up to 300 daily bathers, but by morning no available chlorine was left in the water.

The County Health Department took up to 50 daily samples and found that silver ions remained in the pool at the low, steady rate of 20 parts per billion, with water free of coliform, pseudomonas and staphylococcus bacteria throughout the two seasons. In contrast, 65 water samples from 30 other pools having a mean concentration of 700 parts per billion of available chlorine for disinfection, showed a mean of 1.3 pseudomonas and 7.3 staph cells per millilitre of water.

"This data," the Health Department reported, "indicates that silver is equal to chlorine in maintaining essentially coliform-free pool water, and is somewhat better than chlorine in destroying pseudomonas and staph aureus organisms. The latter two organisms are important from the stand-point of bather health. "During the two seasons with the silver treated pool there have been no eye, ear, nose or throat irritations or infections reported," the Department declared. "It should also be noted that there were no visible growths of algae during the testing period." The Health Department reported its conclusions thus:

"Silver is an effective bactericide for swimming pool water treatment.
"Silver disinfection is easier and safer than other purifying agents.
"Silver does not produce changes in pH thus eliminating the need to add pH adjustment chemicals.
"Silver at prescribed dosages is non toxic to humans."

A reduction in pool maintenance costs also was noted.

How does silver do the job? Last month, Richard L. Davies, Executive Director of The Silver Institute, explained it to the annual convention in Chicago of the National Swimming Pool Institute. Silver acts as a catalyst for oxygen of the air that's dissolved in water, he said; the catalytic action of silver oxidizes the enzymes of bacteria and that kills the bacteria.

At the convention, Davies conferred with Terry R. Jackson of Sherwood Overseas Co. Pty. Ltd. at 49 Bennett St., Perth, W. Australia 6000, which makes pool purification units using silver-copper electrodes; over 10,000 of these units have been sold and produce sparkling, bacteria-free, algae-free water….without chlorine….in swimming pools in Australia, Denmark and elsewhere. Other firms for years have been marketing silver water purifiers in Switzerland, Germany, Japan and Mexico.

Additional confirmation of silver's effectiveness has come from the George Washington University Medical School Microbiology Department which tested the bactericidal effect of hypochlorite alone, compared to hypochlorite in water that also contains 40 parts per billion of silver. When 8,000 E. coli cells were introduced into chlorinated water, the bacteria kill was incomplete after 85 seconds; in water containing the same amount of chlorine plus 40 ppb of silver, the kill was complete in 15 seconds.

American manufacturers of silver water purification equipment include Ionics Inc., of Bridge-ville, Pennsylvania 15017, the firm which supplied equipment for the Allegheny County tests; the Eaton-Jones Co., First National Bank Bldg., Lincoln, Nebraska 68508, which supplied the appliance for the Nebraska test; American Water Purification Inc., of San Francisco, California, which has purified swimming pools for four years; General Ecology Inc., Great Valley Center, Malvern

Doulton Drinking Water Filter Treatment Systems Product Catalog. Includes water purification and drinking water filter systems which use cleanable Doulton ceramic drinking water filter candles and H2O International Inc. drinking water filter cartridges
For more information on health hazards such as chlorine and other drinking water contaminants please read through our "Health Topics" pages or review many of the information sites listed on our research page.

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