Pseudomonas

Pseudomonas bacteria can be found naturally in the ground and within drinking water sources such as aquifers. Conventional drinking water treatment systems can remove or inactivate these bacteria, but they may continue to multiply within finished drinking water attachments and can cause negative health effects in humans under certain conditions.

Elevated numbers of Pseudomonas may indicate the development of a bacterial layer on surfaces within a distribution system. Such surface areas may include home water treatment devices that utilize carbon filters or membranes. However, the presence of disinfectants such as chlorine or chloramines, when applicable, can control (but not prevent) such growth. Furthermore, Pseudomonas species’ ability to slow their metabolism allows them to survive in bottled or distilled waters for months at low densities.

Several guideline values exist for both Pseudomonas and heterotrophic plate count (HPC) measurements, heterotrophic plate count (HPC) being a relatively simple indicator of a wide range of bacteria including several Pseudomonas species. However, health-based limits and mandatory drinking water standards do not currently exist for either. United States federal regulations do not specifically restrict Pseudomonas in drinking water supplies but include the commonly used HPC level of 500 colony forming unit per milliliter (cfu/mL) as an indicator of a sufficient detectable residual disinfectant.