Summer warming of cold water lines: an overlooked hygiene risk

If the temperature in a cold water line is allowed to rise above 25 °C, this can affect drinking water hygiene. This temperature is within the range where Legionella starts multiplying faster.

Although Legionella occurs naturally in drinking water, the bacterium is not usually a health hazard at low concentrations. Things become critical if the microbe starts to proliferate as a result of stagnation or higher temperatures. For optimum growth, Legionella favours temperatures within a range from 25 °C to 45 °C. Temperatures from 35 °C to 45 °C are especially critical.

For operators, this means cold water temperatures need especially careful monitoring in summer, with regular exchanges of water also being essential.

Persistently higher outside temperatures can cause excessive heating of the cold water piping and the water it contains. This effect is often amplified during holiday periods, with many buildings such as schools seeing less use – and therefore less ventilation – during this time. Heat becomes trapped in the building.

For the drinking water installation, the risk of cold water warming in the piping is directly proportional to ambient temperatures near piping runs.

Problematic pipe routing and rarely used tapping points

Alongside high outside temperatures, individual circumstances in buildings can also cause heating to the PWC line. Modern building envelopes are often virtually air-tight. While advisable as an energy-saving measure, this approach can also cause heat to be stored in the building for longer periods. Designs for drinking water installations are also growing more complex. Especially critical are situations where cold water lines are routed into warm areas or are placed very close to lines containing hot fluids or liquids.

Rarely used tapping points further complicate things. During the holidays, schools, sports venues and public-use buildings see significantly lower levels of use – or remain closed all summer. This means water stays sitting in piping for longer.

This results in longer periods of stagnation in the drinking water installation piping with simultaneously higher temperatures for cold water – all making the spread of harmful Legionella bacteria much more likely.

Although stagnation flushes can of course be completed by hand, this can require a significant use of personnel resources – especially in large buildings with many tapping points. Flushes also take time: they must be properly planned, completed and documented.

Water management systems offer a more efficient approach. With the SCHELL SWS Water Management System, all electronic SCHELL fittings in the building can be networked and controlled centrally. This allows flushing to be scheduled or automated in response to temperature changes and with full record-keeping.

SMART.SWS extends this system to the cloud by adding remote management functionality. Operators and facility managers can view, control and log flush operations, fitting parameters and system messages from anywhere in the world. During the holiday period or when outside temperatures start to rise, this flushing schedule can be adjusted accordingly – from a two-day to a one-day cycle, for example. No physical access to the building is required.