Drinking water hygiene: Avoid stagnation & legionella
Legionella in domestic water systems are a serious health risk – and a reality in many single-family and multi-family homes. The bacteria multiply unnoticed in the pipe network and only become a problem for residents when inhaled as a fine spray mist during showering. The main cause is almost always the same: stagnation, i.e., water that remains unused in the pipes for too long.
The good news: Drinking water hygiene is not a coincidence, but the result of correct temperatures, regular use, and suitable materials. This guide shows you how to avoid stagnant water, what regulations apply to owners and landlords, and what is important when renovating domestic water systems.
What are Legionella and how do they develop?
Legionella pneumophila is a bacterium that multiplies in stagnant water systems. Inhalation (e.g., via shower spray) leads to Legionellosis – a severe, sometimes fatal form of pneumonia. Important to know: Drinking water containing Legionella is generally unproblematic; it only becomes dangerous when the pathogens enter the lungs via tiny water droplets. This is precisely why showers are considered the most critical point in domestic water systems.
The multiplication of bacteria follows simple rules: They need time, lukewarm temperatures, and nutrients, such as those found in deposits and biofilms on the inner walls of pipes. A hot water system that is continuously operated at too low a temperature, or a guest bathroom whose pipes remain unused for weeks, thus provides ideal growth conditions. Above the critical temperature zone, on the pathogens reliably die off – which is why the correct hot water temperature is the most important protective measure of all.
- Growth temperature: 25–45 °C
- 100–300 deaths per year in Germany
- Minimum hot water temperature: 60 °C
Caution – increased Legionella risk exists with: too low hot water temperatures (below 60 °C), infrequent use (stagnation), dead legs, and old boilers without thermal disinfection.
Measures against stagnation and Legionella
The most effective protection against Legionella initially costs nothing: water must flow. Every outlet that is used regularly simply flushes away potential sources of germs before they can establish themselves. Critical, however, are the forgotten corners of the installation – the guest toilet, the outdoor tap in winter, or the shower in a rarely used granny flat. Anyone who consciously incorporates such outlets into their routine and flushes them regularly has already managed the biggest risk.
The second pillar is temperature: The hot water tank must be operated hot enough so that Legionella have no chance of survival. The temptation to lower the storage temperature for energy-saving reasons is understandable – but in the drinking water sector, it is the wrong approach. In addition, it is worthwhile to take a critical look at the pipe routing during any renovation: dead legs, i.e., disconnected but not dismantled pipe sections, are permanent breeding grounds and should be consistently removed.
Immediately implementable
- Set hot water to at least 60 °C
- Once a week full steam flush (10 minutes above 70 °C)
- Regularly flush rarely used outlets
- Remove dead legs during renovation
- Regularly change drinking water filters
Structural measures
- Use high-quality stainless steel press fittings
- Use DVGW-certified material
- Plan for thermal disinfection
- Optimize boiler size (do not choose too large)
- Hygiene check every 3 years
Regulations and duties according to TrinkwV
Drinking water is the most strictly controlled foodstuff in Germany – and this responsibility does not end at the house connection. From the transfer point, the owner or operator of the domestic water system is responsible for ensuring that the water arrives flawlessly at every tap. For landlords of multi-family homes, this means specific, regularly recurring inspection obligations, the failure of which can have legal consequences.
Anyone who installs or renovates a drinking water system must also adhere to the recognized rules of technology – from material selection and pipe routing to commissioning. This not only protects the health of residents but also the owner himself: In the event of damage, the standard-compliant execution is the decisive argument against insurance and court.
According to the Drinking Water Ordinance (TrinkwV) and VDI 6023, the following applies:
- Landlords have an inspection obligation in multi-family homes (every 3 years)
- If 100 CFU/100 ml is exceeded, immediate measures are necessary
- Maximum stagnation time 72 hours (DVGW recommendation)
- Drinking water installation only according to DIN 1988 / EN 806
Material selection during renovation
The material question is often underestimated in drinking water hygiene, yet it significantly determines how easily biofilms and germs can settle in the pipe network. Rough or corroded pipe inner surfaces provide bacteria with a hold and breeding ground; smooth, corrosion-resistant surfaces, on the other hand, make it difficult for them. In addition, there is the question of local water quality: Not every material tolerates every water composition equally well.
In the drinking water sector, we recommend stainless steel press fittings (Sanha NiroSan). Stainless steel combines the decisive properties: a permanently smooth inner surface, no release of metals into the water, and full resistance regardless of local water hardness. Those who plan long-term get the most robust solution here – even if other materials have their justification in certain situations.
Advantages of stainless steel
- Smooth inner surface – no bacterial accumulation
- No heavy metal enters the water
- UBA list without restriction
- Over 80 years of service life
- Can be used with any water
Alternatives
- Copper press: fine with hard water, antibacterial
- Multi-layer composite pipe: for floor distribution
- PEX/PE-RT: inexpensive, but shorter service life
A detailed material comparison can be found in the guide Stainless steel vs. copper in drinking water; the connection technology is explained in the article Press vs. solder fittings. Suitable material can be found under Pipes and press fittings and in the category Pipe systems.
What to do in case of a Legionella finding?
A positive Legionella finding is initially no reason to panic, but a clear call to action. It is crucial to protect residents immediately and at the same time find the cause in the system – because disinfection alone only combats the symptom. If the actual weakness remains, such as a dead leg or a tank operated at too low a temperature, the pathogens will return after a short time.
A stepped approach has therefore proven effective: first immediate protection, then disinfection, then structural renovation, and finally control of success through repeated sampling. In rented properties, landlords should also involve the health department and transparently inform residents – this is not only an obligation but also builds trust.
- Immediate measures: Showers with filters, heating above 70 °C
- Thermal disinfection: Run all outlets hot for 24 hours
- Chemical disinfection in case of recurrence (chlorine, hydrogen peroxide)
- Structural renovation: Remove dead legs, renew press fittings
- Recurring control: every 3 months for 1 year
Frequent questions
How often must drinking water be tested for Legionella?
In multi-family rental buildings, every 3 years by the landlord. In a detached house, it is not mandatory, but testing every 5 years is recommended.
What is the correct hot water temperature?
At least 60 °C at the boiler outlet, 55 °C in circulation. This kills Legionella. Lowering the temperature to save energy is not recommended for domestic hot water.
What does a Legionella test cost?
A standard test costs €100–200 per sampling point. For multiple outlets, €500–1,000 in total.
Which material prevents Legionella?
Smooth inner surfaces help: stainless steel is ideal, copper has an antibacterial effect. Plastic is fine, but neutral.
Conclusion
Drinking water hygiene can be planned: 60 °C hot water temperature, regular flushing of rarely used outlets, and the removal of dead legs significantly reduce the risk of Legionella – and most of it costs neither money nor great effort. Landlords should take the statutory inspection intervals seriously, because a documented faultless drinking water system protects residents and owners alike. During renovation, high-quality, DVGW-certified material pays off: Smooth, corrosion-resistant pipe systems permanently deprive germs of their livelihood. Anyone who keeps an eye on temperature, use, and material need not fear Legionella.
Everything for hygienic domestic water systems can be found in the plumbing assortment of wohnungstechnik.de.
