Pseudomonas aeruginosa in a new building at a residential home – thermal disinfection was the answer

For an installation company from Cologne, it was the worst-case scenario: just after completion, contamination with Pseudomonas aeruginosa was found in a new drinking water installation at a residential home. The home’s formal acceptance and commissioning was postponed. The first thermal disinfection had to be stopped – but the second was successful. The nursing home could then finally be commissioned and three acceptance inspections confirmed the successful outcome. 

Case study

Location: Cologne

Type of building: New building at residential home

Problem: PSA contamination in drinking water installation, identified during first test before commissioning

Consequence: Acceptance and commissioning postponed

Solution 1: First thermal disinfection – stopped in new building

Solution 2:Second thermal disinfection in new building – successful

Result: Completion of residential home commissioning

Drinking water installation contamination – what now?

Thermal disinfection is one of the best approaches to decontaminating a drinking water installation that has been compromised by Pseudomonas aeruginosa.

Thermal disinfection

During thermal disinfection, the water in the drinking water installation is heated to kill off the bacteria. This heat penetrates into biofilms and can also kill off bacteria in places where disinfectants are much less effective, such as cracks and under seals, which have no direct contact with water. As Pseudomonas already dies off at 45 °C, a temperature of 60 °C is sufficient for thermal disinfection.

Preparing for thermal disinfection

• Check materials and equipment in the cold water installation to confirm they are heat-proof (e.g. fittings, cisterns, connected appliances like coffee makers)
• Identify all tapping points and ‘dead legs’ – either ‘activate’ these dead legs or remove them
• Structural preparations, to route heated drinking water into the cold water installation – which may require a separate water heater
• Temporary deactivation of anti-scalding protection and cordon off areas as needed to protect residents

Performing thermal disinfection

• Heat up the water and route it into the cold water installation via the entry point
• Every tapping point must be flushed out with the hot water
• Measure the temperature at each tapping point to confirm that the required minimum temperature has been reached
• If the required minimum temperature is not achieved, thermal disinfection must be stopped and restarted (after resolving technical problems)

Important: The thermal disinfection must kill off every single bacterium, because normal cold-water temperatures will be restored after disinfection is complete – there is no ‘follow-up disinfection’ as there would be in the hot water system. 

What is required for a successful thermal disinfection?

• At least 60 °C at every tapping point – with no exceptions
• Thorough check for dead legs – then remove or ‘activate’
• Deactivate anti-scalding protection
• Log water temperatures
• Follow-up inspections are required

Verifying the results of thermal disinfection

Section 5.6 of DVGW W 551-2 (A) requires three ‘acceptance inspections’ after decontamination of a drinking water installation compromised with Pseudomonas aeruginosa:

1. 1st inspection – after 2 weeks
2. 2nd inspection – after 6 weeks
3. 3rd inspection – after 12 weeks

Important: Findings are almost always negative immediately after decontamination – but this may not be the case after 6 or 12 weeks. And that is what matters, after all: decontamination must be permanent!

Note: Even when disinfection is carried out with care, immediate success is less likely in larger buildings. Individual tapping points will often stay contaminated – for reasons that are initially unclear. An explanation is often only found when the entire installation is re-inspected and inspection hatches are opened, leading to the discovery of other relevant issues and circumstances. Once these faults are rectified, repeating the thermal disinfection then achieves the desired results.

Monitor hygiene risks – act to prevent Pseudomonas aeruginosa during normal operations

Prevent outside contamination

To prevent bacterial contamination from parts compromised during production, care should be taken to ensure the hygienic safety of all products installed. This is always the case if manufacturers use dry testing for leak testing instead of wet testing. As SCHELL has proven, this is easy to do in the case of sanitary fittings – Although it is still not an industry standard. 

Some products, however, need to come into contact with water during the manufacturing process – especially in the case of adjustment and calibration work. For these products, DVGW W 551-4 (A) requires a hygiene plan that covers them from the factory to the building site. 

Tip: DVGW W 551-4 (A) and VDI 6023 Part 1 recommend that tender specifications and wholesale orders should include a specific request for products that present no risks to hygiene.

Mandatory inspections

Inspections are mandatory for buildings classified as ‘priority public facilities’. In the case of new developments or major renovations to the drinking water installation, facilities must be inspected for the presence of Pseudomonas aeruginosa at least once a year.

Priority public facilities (DVGW W 551-4):

• Hospitals and nursing facilities (nursing homes for the elderly, residential nursing homes)
• Ambulatory care clinics, dialysis centres, same-day clinics, birth centres, rehabilitation facilities
• Day nurseries

Note: DVGW W 551-4 (A) (published March 2024) provides all of the relevant information, and a detailed discussion of approaches to avoiding and resolving cases of contamination. It is the definitive reference on this bacterium for the sanitary equipment industry.