DEKRA issues warning regarding Legionella in drinking water
Danger of Leaving Water in Water Pipes to Stagnate
- Be aware of the risks when returning from vacation or a business trip
- Up to 30,000 Legionella infections are recorded each year
- After being away for an extended period (of up to seven days), allow water to flow for at least five minutes upon your return
If you are away from your home for an extended period of time, it is advisable to ensure you have fresh, uncontaminated drinking water upon your return. If water in water pipes is left to stagnate for long periods, there is an increased likelihood of contamination from Legionella bacteria. As an expert inspection company, DEKRA wishes to reiterate the warning that Legionella contamination can result in dangerous pneumonia. According to estimates from the Robert Koch Institute, around 15,000 to 30,000 people in Germany are affected by this condition every year.
As per the German Ordinance on the Quality of Water Intended for Human Consumption (Trinkwasserverordnung, abb. TrinkwV), operators of buildings with more than two residential units and hot water systems of a certain size or larger are obliged to have drinking water sampled and analyzed by accredited laboratories at intervals of up to three years. Many properties will again be affected by this in 2025.
What is Legionella?
Legionella are widespread bacteria that are found in small quantities in lakes, rivers, and groundwater, as well as in moist soil or compost. Although these germs are normally harmless, they can become a threat to human health when circumstances allow them to multiply rapidly.
One such condition in which Legionella quickly spreads is stagnant water. If the temperature of the water is between 30 and 45 degrees Celsius, this provides an optimal breeding ground. "The reasons for increased Legionella findings are complex, and often come down to an interplay of incorrect system operation, outdated or defective system technology, and inadequate maintenance," explains Stefan Schüttler, a DEKRA expert on the subject of drinking water.
Severe lung diseases are possible
If water droplets (aerosols) from contaminated drinking water systems get into a person's respiratory tract – e.g. when showering – they may become infected with Legionella. The consequences of such an infection can include Pontiac fever or pneumonia. Older or immunocompromised people are particularly at risk from this.
Preventing infections
"If no water is drawn from a drinking water system for an extended period of time, this can encourage the proliferation of Legionella. Therefore, if you've been away for a while, it's essential to flush the pipes upon your return and replace the water that has been left to stagnate with fresh water," says Schüttler. Depending on how long you've been away for, you'll need to take the following measures:
- Even water that has been left to stagnate in pipes for four hours or more – up to a period of three days – must be drained away.
- If the water has been left to stagnate for more than three days – up to a period of seven days – the user must open the taps completely and allow the water to run for at least five minutes. This applies for both cold and hot water.
- If the drinking water installation is left unused for up to four weeks, it must be flushed professionally.
- If it has not been used for more than four weeks, additional microbiological tests will be required.
- In general, faucets in the kitchen, bathroom and shower all need a supply of fresh water. The drained water can be used for other purposes, such as for cleaning or for watering flowers.
What to do if a build-up of Legionella is discovered
The TrinkwV specifies a limit of 100 CFU (colony-forming units) per 100 milliliters for Legionella in a drinking water installation. If this value is exceeded, the laboratory is obliged to forward the test results to the responsible health authority without being requested to do so. The operator of the water supply system must – without being requested to do so and without delay – prepare a risk assessment, e.g. with the assistance of experts from DEKRA.