The San Francisco Public Utilities Commission (SFPUC) continues its commitment to provide safe, high quality drinking water through aggressive watershed protection and appropriate water treatment.  While tap water is safe, it is not sterile.  People with weakened immune systems may be more vulnerable to biofilm contamination than others and should seek advice about protective measures, including drinking water, from their health care provider.   The SFPUC continues to assess the potential for biofilm growth and its management as it studies new treatment technologies.

What are Biofilms?

Biofilms are generally thin layers of microorganisms that have attached to and grow on surfaces. Not only do biofilms consist of organisms, they also are comprised of pieces of metals from pipe corrosion, organic and inorganic matter, and microorganism by-products that bind the colony together (called extra-cellular material). Biofilms can grow in water distribution mains, indoor plumbing, within water fixtures (i.e. shower heads and faucets) and on surfaces.

Biofilms can consist of a variety of organisms at any one time, some that can cause illness, particularly in individuals with suppressed immune systems.

How Does a Biofilm Form?

A biofilm forms when sufficient numbers of an organism enter a water system (through either unfiltered water, a treatment deficiency, new construction, or other manner) and settle into a location where attachment and growth is possible. Factors that promote biofilm growth include corrosion (provides crevices for attachment), presence of nutrients, elevated temperatures, and low disinfectant levels.

Large buildings, particular those with recirculating hot water systems, and building and homes located towards the end sections of distribution systems are more susceptible to biofilm growth. Hospitals, due to the high density of immunocompromised individuals, are key locations where biofilm-associated illnesses have occurred.

Why are Biofilms a Concern?

The concern with biofilms is not necessarily from the organisms in the film, but from microorganisms that slough away from the biofilm and enter the main water stream. Some of these organisms can be pathogenic.

What Threat are Biofilms to My Health?

Biofilms can contain a host of different microorganisms that have potential health significance. Most notable ones are Legionella pneumophila and Mycobacterium avium complex. These organisms can grow within a biofilm and then slough away into the water stream where they can either be ingested or inhaled (i.e., aerosols from showers and humidifiers). Often no disease symptoms will result. On occasion, however, health effects range from gastrointestinal illness (from ingestion) to pneumonia (from inhalation of aerosols).

How Can I Protect Myself?

If you are immunocompromised you should consider additional protective steps such as boiling your drinking water for one minute, which will kill any bacteria in it. You could also use a water filter certified by NSF International to remove particulate matter, 1 micron absolute in size (Class II), or drink only bottled water certified by NSF or canned and bottled bubbly drinks.

In using a home water filter, it is critical to replace or clean the filtering mechanism per the manufacturers instructions. If filters are not changed or cleaned regularly, the filter itself can be colonized by biofilm microorganisms and begin to pose a health threat.

For Further Information

• Call NSF International to learn more about water filters and bottled water (1-800-673-8010)
• Call the San Francisco Public Utilities Commission Water Quality Bureau for water quality information (650-652-3127 or 1-877-737-8297)
• Call the Environmental Protection Agency (EPA) Safe Drinking Water Hotline for information on water quality and associated regulations (800-426-4791)
• Call the Centers for Disease Control and Prevention (CDC) if you have a severely compromised immune system and would like further information (1-800-232-4636)

References

Geldreich, E.E., 1991. Opportunistic Organisms and the Water Supply Connection. Proceedings from the American Water Works Association, Water Quality Technology Conference, November 10-14, 1991, Orlando, Florida.

LeChevallier, M.W., Olson, B.H., McFeeters, G. A. 1990. Assessing and Controlling Bacterial Regrowth in Distribution Systems. American Water Works Association Research Foundation, Denver, CO.