Drinking water temperature: what reaches the tap and which values apply

In German buildings, cold tap water is usually between 13 and 19 degrees Celsius. The middle half of 280 readings from a research project fell within this range. The exact value depends on where it is measured. Where the water enters the building, the median is 14.2 degrees; at the tap in the flat, it is 17.4 degrees.

Both values come from a research project that took measurements at field sites across Germany in 2018. A single average value says considerably less. What matters is whether your water stays cold enough.

The technical rules assume a design value of 10 degrees Celsius at the service connection, because groundwater stays cooler than the air above it. Measurements show something different. In 2018, a joint research project of the Technische Universität Dresden documented the temperature at every sampling. Its title is “Energieeffizienz und Hygiene in der Trinkwasser-Installation” (Energy efficiency and hygiene in drinking water installations).

The table shows three things. First, the water arrives in the building warmer than the design assumes. More than two thirds of the central cold water samples were above 10 degrees. Second, at the tap the median is 3.2 kelvin higher than at the building entry. Third, the upper quarter of readings at the point of use starts at 20.5 degrees, and the highest single reading was 33.3 degrees.

The peak values of 58.2 degrees at the central measuring points are not cold water temperatures in the literal sense. They occur where heat from the water heater flows back into the cold water side.

An average of 15 degrees accurately describes the mean of this series of measurements. But it conceals precisely the cases that matter.

There are often 20 metres of pipe between the service connection and the tap. Along the way, 4 heat loads regularly occur.

• Shared shafts. If cold water, hot water and heating pipes run in the same riser shaft, the cold water heats up.
• Suspended ceilings and false walls. Heat builds up there, sometimes intensified by built-in light fittings.
• Warm plant rooms. If the distribution system is located in a heated basement room, the warming already starts there. Copper pipes also pass the heat of the room on to the water.
• The tap itself. If the hot water circulation is connected directly to the wall plate, the tap body transfers heat to the cold water connection.

A fifth cause is stagnation. If the water stands in the pipe overnight, its temperature adjusts to that of its surroundings. After a weekend in a warm flat, the cold tap initially delivers water at room temperature.

DIN 1988-200 sets an upper limit of 25 degrees Celsius at the point of use for cold drinking water. Guideline 6023 Part 1 sets the bar lower. It comes from the Verein Deutscher Ingenieure (VDI, Association of German Engineers) and the Deutscher Verein des Gas- und Wasserfaches (DVGW, German Technical and Scientific Association for Gas and Water) and recommends a maximum of 20 degrees.

What the 25 degrees mean in practice is set out in the recommendation of the Umweltbundesamt (German Environment Agency) on systemic testing for legionella of 18 December 2018. It states that under certain conditions it is also necessary to test the cold drinking water installation, “e.g. if a water temperature of 25 °C or higher is found after flushing the points of use for 30 seconds”.

The figure therefore marks a trigger and does not describe a comfort level. Anyone who measures 25 degrees after flushing for half a minute has a finding. It entails further investigations.

The reason lies in the growth range of bacteria. They settle as a biofilm on the inner walls of pipes: besides legionella, for example Pseudomonas aeruginosa. The Umweltbundesamt describes the risk as particularly high “when water stagnates in pipes for days at temperatures between 25 and 55 degrees Celsius”. From the median at the point of use, that is 7.6 kelvin away. For the upper quarter of readings, it is 4.5.

One restriction is noteworthy: the current version of the same recommendation, dated 13 October 2025, explicitly excludes the assessment of legionella in cold drinking water. The 25-degree mark remains anchored in the standard and the guideline. It no longer appears in the current testing recommendation.

For hot water, the direction is reversed: it has to be hot enough. The Umweltbundesamt gives 2 values. At least 60 degrees Celsius must be maintained at the outlet of the water heater. Throughout the entire pipe system, the hot water should stay at 55 degrees or more.

Both limits serve hygiene, not comfort. Below them begins the range in which legionella multiply. Inhaled as a fine spray, they can cause pneumonia. The disease is called legionellosis. The field measurements show how often the target value is missed. Contaminated hot water samples had a median of 48.7 degrees, uncontaminated ones 53.1 degrees. The difference is 5.4 kelvin.

In cold water, the same comparison turns out differently. There, the contaminated samples had the lower median temperature, 14.2 versus 16.2 degrees. For cold water, temperature alone therefore does not account for the finding; it acts together with stagnation time and pipe routing.

Anyone who lowers the hot water temperature to save energy is therefore trading costs for risk. Hot water accounts for around 12% of the energy consumption of private households, and with electric water heating even around 25% of the electricity consumption of a two-person household. The Umweltbundesamt nevertheless expressly advises complying with the hygiene requirements and saving elsewhere instead.

The Trinkwasserverordnung (German Drinking Water Ordinance) contains no temperature value for cold or hot water. A full-text check of the version currently in force confirms this. Temperatures appear 26 times in it, all in a different context. They refer to the laboratory incubation temperatures of 22 and 36 degrees and the reference temperature of 25 degrees for electrical conductivity.

What is regulated instead is the consequence of excessively high temperatures. Annex 3 Part II sets a technical action value of 100 colony-forming units (CFU) per 100 millilitres for Legionella spec. If it is reached, the obligations to act under § 51 apply. The operator must report the finding to the health authority and clarify the cause. This involves checking whether the system complies with the generally recognised rules of technology.

Temperature itself reappears elsewhere. The recommendation of the Umweltbundesamt, which is binding via § 43 paragraph 5, makes temperature measurement a mandatory step in every sampling. Two values are documented: the sampling temperature and the temperature once it has stabilised.

More on how the ordinance is structured can be found in our article on the Drinking Water Ordinance.

§ 31 of the Drinking Water Ordinance links the testing obligation to 4 conditions, all of which must be met.

1. The drinking water is supplied as part of a commercial or public activity.
2. A storage water heater or central instantaneous water heater holds more than 400 litres. Alternatively, a pipe between the heater and the draw-off point contains more than 3 litres. The circulation pipe is not counted.
3. There are showers or other facilities in which drinking water is atomised.
4. The building water supply system is not located in a single- or two-family house.

The Bundesministerium für Gesundheit (Federal Ministry of Health) summarised how this is to be interpreted in practice, as of 10 October 2023. According to this, even renting out a single privately owned flat counts as a commercial activity. If, on the other hand, all the owners live in their flats themselves, no obligation arises.

The frequency depends on the type of use. For public activities, testing is required at least once a year; for purely commercial activities, at least every 3 years. Schools, kindergartens and hotels, for example, count as public activities. After three years without any deficiencies, the public health office can extend the interval to up to 3 years. For hospitals and care facilities, the interval remains annual.

For your own household, this means: as the owner of a single-family house, you are not subject to any testing obligation. Responsibility for the temperatures in your installation nevertheless remains with you.

The season affects the network less than the building. Underground, the temperature remains comparatively stable throughout the year. Even so, the range measured at the building entrance extended from 6.4 to 23.3 degrees Celsius.

One research project measured more than 25 degrees during the summer months, even in the suppliers' pipe networks. The causes are thought to be climate change, with rising ground temperatures, and less mixing in reservoirs and lakes.

Inside the building, the effect is more pronounced. In summer, room temperatures rise in shafts and utility rooms. This is exactly where cold water loses its advantage. Guideline 2050 Part 1 therefore limits the room temperature in plant rooms with drinking water distribution to 25 degrees.

In practical terms, this means: in winter, the water comes out of the tap cooler, in summer warmer. The difference arises mainly over the last few metres.

A thermometer and 2 minutes of your time are all you need. The procedure is based on what also happens during official sampling.

1. Open the cold tap fully and let the water run for 30 seconds. For official sampling, the aerator is removed first; in everyday use, a clean spout is sufficient.
2. Fill a container and measure immediately. The reading corresponds to the sampling temperature.
3. Let the water keep running until the temperature stops falling, then measure again. This is the constant temperature.

The second value shows what your own pipe delivers. The first value shows what was standing in the pipe. If it is 25 degrees or more after 30 seconds, that is a finding. The Umweltbundesamt's recommendation treats it as grounds for further testing.

Measure at a cold tap without a mixer, or close the angle valve of the hot water supply. A mix of hot and cold distorts the result.

A reading above 25 degrees Celsius usually points to the installation inside the building, less often to the network upstream. 5 steps will help.

• Let the water run. The Umweltbundesamt advises drinking only fresh, cool water from the tap. After the water has been standing for a long time, let it run until it becomes noticeably cooler.
• Flush rarely used pipe runs. A guest bathroom, holiday flat or little-used connection needs a regular change of water.
• Check the insulation. Cold water pipes need to be insulated just like hot water pipes, especially in shared shafts.
• Call in a specialist firm. If the values remain high, the pipe layout should be checked. This is not a DIY job.
• Inform your landlord. In a rented building, the operator's obligation does not lie with you, but reporting the finding does.

In addition, fill cooking pots from the cold water pipe. Hot water has passed through the water heater and may have been standing there for some time.

There is no standard value for taste. It is widely stated that water tastes best at between 8 and 12 degrees Celsius. This is based on experience, not on any regulation.

What is proven, however, is the link with freshness. The Umweltbundesamt puts it concisely and advises drinking only fresh, cool water from the tap. Water that has been standing in the pipe for a long time absorbs heat and, depending on the pipe material, also heavy metals from the installation.

We cover how temperature affects the pH value in our article on the pH value of water. Which substances are found in tap water in the first place is explained in our overview of substances in tap water.

Note on the standards: the texts of DIN 1988-200 and Guideline 6023 Part 1 are subject to a fee. They were not available to us in the original. The values of 25 and 20 degrees are based on the Umweltbundesamt's recommendation and the specialist article.