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Drinking water hygiene and Legionella contamination in water heaters – a look at holiday homes

Tankless or mini tank water heaters are popular solutions for supplying hot water as they have a compact form factor and are easy to retrofit. In the past, most building operators also typically assumed – in the absence of mandatory testing regulations – that they were perfectly safe when it came to concerns about drinking water hygiene. However, experts have long since warned about the dangers of making such an assumption. As the authors of the ‘LeTriWa’ study have shown, the assumption ‘no mandatory testing = no problems with Legionella’ is clearly wrong. In this article, we present an interesting example from practice that shows how drinking water quality can be supported with the help of automatic stagnation flushes.

Legionella is a risk in drinking water installations not subject to mandatory testing

Most decentralised tankless water heaters are certainly hygienically safe as long as they are operated according to regulations at all times – including the tourist season. In terms of building stock in Germany, however, we can’t be 100% sure of this, because section 31 of the German Drinking Water Regulation (TrinkwV) only stipulates mandatory testing annually or every three years for large water heater installations. As a result, the large proportion of drinking water installations classified as ‘small systems’ or with decentralised water heaters are only inspected in suspected cases of Legionella. As the LeTriWa study from the Robert Koch Institute (RKI) and the Federal Environment Agency (UBA) has shown, this has serious consequences: 43 percent of the 111 patients and fatalities investigated by the study became infected with Legionella at home from systems not subject to mandatory testing.

Legionella

Although overlooked in relation to decentralised water heaters to date, Legionella spp. pose a serious risk to human health even in installations not subject to mandatory testing.

Insights from practice with decentralised water heaters: a look at holiday homes

For this reason, the study authors from the RKI and UBA call for investigations into Legionella infections to be extended to installations that are not subject to mandatory testing. In doing so, they confirm the results obtained by Professor Martin Hippelein in 2016. Investigating two cases of Legionella infection, Hippelein looked at a residential building with 84 units and decentralised water heaters. The 3-litre rule set out by DVGW W 551 (A) had been followed. The residential units were primarily used as holiday home rentals. Hippelein found that, regardless of the hot water temperature (i.e. whether below or above 50 °C), Legionella contamination tended to spread excessively if normal operation had not been maintained as specified via the tapping points. The findings were truly alarming: testing for Legionella revealed that 54 percent of the apartments had concentrations above the technical action value, while 12 percent of the apartments even had values above the risk threshold of 10,000 CFU/100 ml. In the latter case, showering must be prohibited or terminal sterile filters must be fitted.

Maintaining drinking water hygiene with contactless fittings

To avoid incidents as described in the LeTriWa study and by Prof. Hippelein, building operators are advised to perform regular stagnation flushes, such as every 72 h after the last usage. This is especially important in residential units like holiday homes that have irregular usage patterns. During periods of absence, these flushes ensure the automatic exchange of stagnating and therefore potentially contaminated water. Contactless fittings are therefore also recommended for use in holiday homes. For kitchens, one example is the multiple award-winning GRANDIS E from SCHELL: this hybrid tap can be operated either with its conventional single lever or by its infrared sensor. Any building operator needing a record of flushes performed can fit a Bluetooth® module between the power source (battery or mains) and the fitting. This module features calendar, scheduling and logging functions.

GRANDIS-E

The choice is yours: the GRANDIS E kitchen tap can be operated either with a single-lever mixer or with an infrared sensor – and is also compatible with the SCHELL SWS Water Management System.

In larger properties, the recommendation is to network SCHELL electronic fittings using the SWS Water Management System. SWS offers building operators and facility managers many benefits for the efficient and cost-effective operation of drinking water installations.

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