Silver Inhibits the Growth or Bacteria in Water Filters, But It Is Not a Serious Biocide

Silver has for some time been used as an ingredient in water filters, especially carbon drinking water filters and ceramic filters.

It is also used in swimming pool purification devices.

When silver is used in a water filter, the EPA regulates it as a pesticide, so an EPA approval often appears on the product label. This has led to a false notion among the public (which is encouraged, I regret to say, by some manufacturers of water filters that contain silver) that such products are “certified” by the EPA as a guarantee of performance.  The EPA does not certify the performance of any product.  The EPA approval merely means that the filter contains so little silver that its water can be consumed safely by humans.

Silver is often added to ceramic filters to prevent bacterial grow through.

Another common false belief about silver in water filters is that it “kills bacteria,” meaning that it makes unsafe water safe to drink.  It does not.  Silver is classified as a “bacteriostatic” agent, not a biocide.  This means merely that it inhibits the growth of bacteria in existing filter beds.  For that reason it is sometimes added to carbon filters, since carbon provides a fertile growing place for harmless, non-pathogenic. heterotrophic bacteria.  Silver serves as a bacteriostatic agent, inhibiting that growth.  It can also serve a useful function when it is embeded  ceramic filters, where it can prevent bacteria from growing through the ceramic wall.

Although recent studies indicate that if given enough time silver can produce a 6 log reduction of bacteria, it is an extremely slow acting killer and its usefulness in this area is very limited.