Accreditation: UKAS accredited for potable, process & swimming pool waters.

Sample volume: 100mls

Turnaround time: 1-5 days depending on the method

Expression of results: cfu/100mls or MPN/100mls


Many species of Pseudomonads occur naturally in ground and surface waters. Some of these may survive the treatment process or may be subsequently introduced into treated water as a result of contamination. In many cases this may not be a problem but if growth is sufficient the result may lead to a deterioration in quality that may be reflected in an unacceptable taste and odour, without necessarily being a risk to health. In some mains water supplies low numbers of Pseudomonads are quite common and form part of the normal bacterial population.

The Pseudomonas group are widespread in nature occurring commonly in water and soil, and on damp or moist surfaces. When these organisms are present they may proliferate utilising nutrients either from the water or from plumbing materials used in the distribution system. Similarly they may growth in water contained in bottles (particularly plastic) and on surfaces such as plastic tubing and filters within drinks vending machines. These machines often contain a carbon filter the purpose of which is to remove any unwanted taste such as chlorine or the inherent taste of the water. However, these filters efficiently remove chlorine – the means of controlling bacterial numbers, as well as adsorbing bacterial nutrients onto the surface of the carbon. The net result is that these filters have the ability to support the growth of high bacterial number including Pseudomonads. In order to prevent this occurring, it is important that if filters are fitted, they are maintained or replaced in accordance with the manufacture’s recommendations. This group of organisms will readily grow on any damp or moist surfaces; they are also known to be coated in a slime-type layer comprised of polysaccharides (sugars). It is this coating that makes these organisms significant in the formation of slime layers within water distribution systems and the subsequent formation of a biofilm. The presence of Pseudomonads in mains water can be problematic if closed systems etc. are being charged with mains water containing these organisms, and the water treatment specialist is aiming for a Pseudomonas-free system.

Pseudomonas aeruginosa is ubiquitous in fresh water, sewage and soil and can also be derived from faeces of animals and humans. This organism can grow in low nutrient environments and can survive many months in water at ambient temperature. It is an important opportunistic pathogen and is particularly significant cause of hospital acquired infection. This is because of their resistance to many antibiotics and disinfectants and their ability to colonise aquatic low nutrient environments. However the vast majority of people exposed to this organism suffer no adverse health effects. Non- hospital acquired infections are often localised and are associated with contact with contaminated water. Although P.aeruginosa can be present in drinking water in small numbers the organism is not generally infectious if swallowed with the possible exception of profoundly immuno-compromised individuals. The numbers present in mains water are unlikely to be sufficient to cause infection unless they are allowed to multiply. However, taps can become locally contaminated with this and other organisms.

Routine testing of mains water for this organism is not recommended, but in view of its importance as an opportunistic pathogen testing may sometimes be required when water may be implicated as the cause of illness.

In order to minimise the growth of Pseudomonads within a system, filters etc should be maintained appropriately correct plumbing material employed, and the stagnation of systems and tanks should be avoided, and dead legs should be removed.