The pH value of water: why the limit value protects the pipes

The Trinkwasserverordnung (German Drinking Water Ordinance) allows tap water a pH between 6.5 and 9.5. Munich measures an annual average of 7.56, Dresden's mixed water 8.0. In 71 Saxon supply zones, the value lies between 7.2 and 8.5, i.e. within less than a third of the permitted range. This narrowness is no coincidence. The pH is in the Ordinance because it helps determine how much metal the pipes release into the water. It is not a health risk in itself, and the World Health Organization has therefore deliberately not given it a guideline value.

Stadtwerke München (Munich's municipal utility) measures an annual average of 7.56, with a minimum of 7.42 and a maximum of 7.78. The Free State of Saxony publishes values for 80 supply zones, 71 of them with a pH reading. Their median is 7.90, and the range extends from 7.2 to 8.5.

62 of these 71 zones are at 7.7 or above. At the lower end are the Jahnaaue mixed water and the Johnsdorf-Drehe waterworks, each at 7.2; at the upper end is the Freiberg mixed water at 8.5. The Dresden mixed water zone, supplied by the Coschütz, Hosterwitz and Tolkewitz works, reaches 8.0 with a total hardness of 8.3 degrees of German hardness. The Saxon figures are annual averages from 2020.

There is no nationwide database for the pH of drinking water. If you need the value for your own address, you will find it in your local supplier's analysis. Most publish it as a PDF, often together with the hardness and conductivity.

The overview lists 11 values between pH 1.0 and 9.5 side by side, from gastric juice to the upper limit value of the Drinking Water Ordinance. Each row names its source, because pH comparison tables usually leave this open.

An assessment basis issued by the Umweltbundesamt (German Environment Agency) governs which metallic materials may come into contact with drinking water. It was last amended on 26 February 2026. It makes copper pipes subject to a condition with two branches. Either the pH value is 7.4 or higher. Or it lies between 7.0 and 7.4, and the organic carbon content remains at no more than 1.5 milligrams per litre.

If either of the two conditions is met, the water will generally comply with the copper limit from the 16th week after new installation at the latest. Otherwise, the material is considered restricted for that supply area, and the specialist planner must refer to available measurements of copper release. The pH value therefore helps decide what can be installed in the building.

Galvanised steel pipes follow a different logic, and this is where a widespread rule of thumb gets it wrong. The assessment basis does not specify a pH limit for hot-dip galvanised ferrous materials. It requires a base neutralising capacity up to pH 8.2 of no more than 0.20 millimoles per litre and a neutral salt quotient below 1, as well as restriction to cold water. If you set the Munich measurement against this, the result is a base neutralising capacity of 0.4 millimoles per litre, twice the threshold mentioned. This comparison is our own, not the supplier's.

Internally tinned copper is not subject to any such restriction, provided the tinning complies with the relevant technical rules.

In 2007, the World Health Organization deliberately did not set a health-based guideline value for pH in drinking water. Instead, it describes pH as one of the most important operational parameters. Any effect on health is likely to be indirect, it says, resulting from metals taken up from pipes and taps or from inadequate disinfection.

A higher pH often goes hand in hand with greater hardness, but the relationship is not fixed. Munich combines 7.56 with 15.8 degrees of German hardness, the Dresden mixed water 8.0 with 8.3 degrees. Here, the higher pH belongs to the softer water. At 14 degrees of German hardness, Berlin lies between the two.

Both variables are linked through the same chemical system, the equilibrium between lime and carbonic acid. Dissolved carbon dioxide forms carbonic acid in water and lowers the pH. This carbonic acid dissolves lime from the rock, which increases the hardness and raises the pH again. Which of the two effects prevails depends on the underlying geology.

In practice, this means that pH alone does not tell you how high in limescale the water is. For that you need the hardness, which is listed in the same analysis.

The Umweltbundesamt measures precipitation at stations including Westerland, Waldhof and Schauinsland and reports a pH of 5.4 for 2024. In the 1980s, it was between 4.1 and 4.6 at the same stations. The reason for the rise is the fall in sulphur dioxide emissions from 5.5 to 0.2 million tonnes between 1990 and 2024, a drop of more than 96%.

Behind this is the same mechanism as with distilled water. Freshly distilled, it has a pH of 7. As soon as it is exposed to air, it absorbs carbon dioxide, forms carbonic acid and becomes acidic. If you find distilled water listed with a value of around 5, you are seeing the result of this contact, not a property of pure water.

Sparkling mineral water follows the same rule, only deliberately induced. Adding carbon dioxide lowers the pH, which is why sparkling waters are lower than their still counterparts. The exact value is given in the analysis on the bottle label.

Acid rain as an explanation for acidic groundwater is therefore largely a thing of the past. Where raw water arrives too acidic today, this is usually due to the underlying geology, for example in low-lime upland areas.

For home use, test strips that show the pH value through a colour change are sufficient. They cost a few euros and typically resolve in steps of 0.5. To find out whether your own water lies within the range set by the Ordinance, a single sample tested this way is enough.

Anything more precise requires a glass electrode. Laboratories use it to measure electrometrically and achieve two decimal places. Temperature has a noticeable effect on the result, which is why precise devices measure it at the same time and compensate for it mathematically.

Three things distort any home measurement. Water that has been standing in the pipe for a long time has changed chemically, so run it off first. Carbonated water loses gas when poured into another container, and its pH rises as a result. And a strip that has been lying open in the kitchen will eventually show all sorts of things. If you need precision, turn to the supplier's analysis or a laboratory test.

Swimming pools follow a different target value from drinking water, and the reason is disinfection. The higher the pH, the less effective chlorine becomes; the World Health Organization gives a value below 8.0 for effective chlorine disinfection. The binding rules for pool water treatment are set out in DIN 19643. If you adjust your pool, you are working on disinfection performance, not drinking water quality.

In an aquarium, the target value depends on the animals and plants living in it, and it varies considerably with the stocking. There too, tap water is only the starting point.

Finally, body pH is not a water parameter. Blood lies at 7.35 to 7.45, gastric juice at 1.0 to 3.5. Neither of these values follows what you drink. These three questions have nothing in common with the value from your own pipes except the name.

An activated carbon filter on the tap does not shift the pH value to any significant extent, and it is not meant to. The value is set at the waterworks to 7.7 or higher so that the pipe network remains protected. That is exactly the value that is meant to reach you.

A filter becomes effective at the point the World Health Organization identifies as the actual health pathway: the metals from the domestic plumbing. The water supplier is responsible up to the building's service connection; after that, your own pipes decide what arrives. An activated carbon block filter directly at the point of use works in exactly this zone.

There are two things it does not do. It does not replace running the water off after a long period of standstill, because stagnant water has already taken up metal. Nor does it help against legionella, because their growth depends on temperature. They find ideal conditions between 25 and 45 degrees Celsius. Above 55 degrees, growth is inhibited. None of this has anything to do with pH.

If you want to know whether a filter is worthwhile for your situation, start with the supplier's analysis and the age of your own pipes.