Chlorinated drinking water: technical solutions being tested
26.09.2025 – Why some of Offenbach's drinking water has been chlorinated for several weeks was the subject of an information event on Wednesday, September 24, in the Bernardbau.
In addition to attendees from politics and the city administration, around 40 citizens took the opportunity to ask representatives of the Zweckverband Wasserversorgung Stadt und Kreis Offenbach (ZWO), the Hessenwasser company and the city health department their questions. The main focus was on possible technical alternatives and health issues. The information event took place at the invitation of Mayor and Head of the Health Department Sabine Groß, who showed great understanding right at the beginning for the fact that the chlorination of the newly supplied drinking water came as a surprise and caused irritation: "We have never had chlorinated drinking water in Offenbach before and that is not what we want," said Groß "Drinking water tests by the city health department have shown that the chlorine content is far below the already very strict limits in Germany. The water is hygienically flawless. Nevertheless, this event is important to me in order to address the concerns and fears of the population and to discuss which alternatives to chlorination are conceivable and being examined in the future."
On behalf of the ZWO, which is responsible for the drinking water supply in the Offenbach city area, Deputy Association Chairman Peter Schneider once again apologized for the initial lack of communication regarding chlorinated water. "We clearly failed to inform the public in advance, and we will do better in future." Schneider also emphasized that the ZWO made a conscious decision to purchase additional water: "The sources from which the ZWO has been pumping its water to date are limited. We are not allowed to pump more water from our own wells due to the declining groundwater trend. As this is unlikely to change in the future due to climate change, the ZWO must access additional sources to ensure that everyone has drinking water at all times. That is why we are now also purchasing from Hessenwasser - a conscious decision in terms of sustainability, so as not to tap into the groundwater of other regions." At the same time, he emphasized: "The drinking water supplied by Hessenwasser is of the highest quality."
Drinking water strictly monitored
Drinking water is one of the most strictly monitored foodstuffs in Germany. The chlorine content of the drinking water supplied in Offenbach is well below the permitted limits - it therefore fully complies with the Drinking Water Ordinance, which stipulates that drinking water must not contain any pathogens or substances in concentrations that are harmful to health.
Since August 2025, the ZWO has been receiving additional drinking water from Hessenwasser in order to guarantee security of supply in the long term and reliably cover the increasing demand. This water, which flows into the Offenbach pipeline network at the Kaiserlei transfer point, mainly comes from the Hessian Ried and the Frankfurt city forest. It flows via two main pipes along the Nordend, initially to the east in the direction of the harbor island. By changing the intake, for example at night or at weekends, softer spring water from Hessenwasser's Main-Kinzig extraction area can also flow into the upstream network via the same transfer point at Kaiserlei. Both waters contain low concentrations of chlorine. "Chlorination is carried out as part of the risk assessment that we carried out together with the health department of the city of Frankfurt, and it ensures that the water remains hygienically flawless at all times," said Elisabeth Jreisat, Managing Director of Hessenwasser, at the event, emphasizing: "The smell of chlorine can be more noticeable with soft water than with harder water."
The ZWO itself supplies a total of around 21 million cubic meters of water per year - 500,000 cubic meters are now supplied by Hessenwasser at the Kaiserlei transfer point, and only this is chlorinated in low concentrations. Peter Schneider explained why the chlorine can be smelled so clearly, especially at the taps in Offenbach harbor: "We have been researching the causes over the past few weeks. The flow of water in the pipe network is very complex and difficult to calculate and influence due to fluctuating consumption by households and businesses depending on the time of day. We therefore have to look at the actual conditions and draw conclusions from them. As far as we know at present, one of the main reasons for the greater impact on the port is probably the exposed location of the port island, to which only one central water pipe leads. In addition, there are relatively new house pipes here that do not yet have a helpful biofilm." In Nordend and the other western districts, on the other hand, the water from Frankfurt, which is fed into the Offenbach pipeline network at Kaiserlei, mixes much more with the unchlorinated water supplied by the ZWO, Schneider continues: "The reason for this is the much more branched pipeline network outside the port. This means that the already low chlorine content elsewhere is reduced to such an extent that it is no longer detectable in the ZWO's measurements."
Some of the citizens present expressed concern that chlorine could still reach other parts of the city in the future. Schneider made it clear: "The chlorinated water is discharged at a single transfer point in the very west of the city at Kaiserlei. However, this is only a very small proportion of the total volume of water that the ZWO discharges into the Offenbach network. The Offenbach city area is mainly supplied with water from the elevated tank on Bieberer Berg. This water is not chlorinated and this will not change."
Test to eliminate the chlorine odor
Schneider and Jreisat assured that both the ZWO and Hessenwasser are currently examining various technical options that could eliminate the smell of chlorine from the water in the port area. These include, for example, controlling the water flows in the Frankfurt city area so that the chlorine is no longer noticeable in the Offenbach network. Initial tests in recent days have shown that chlorine was therefore no longer noticeable at the port at some times. Further adjustments will be made to the water mixture over the next six weeks. However, it is by no means certain whether this will permanently eliminate the smell and taste of chlorine.
Another conceivable solution is the installation of a device to vent the water pipe on the harbor island, through which the free chlorine can escape. The construction of a ring main is also to be examined. This would certainly be expensive, especially as it could not be realized via the harbour bridge for structural reasons. In addition, the solution would be subject to the proviso that the water would not be able to mix as much as in Nordend, for example. The ZWO is also looking into installing an activated carbon filter to filter the chlorine out of the water completely. "In principle, every household can install such a filter in their own water pipe. But we want to find a solution for everyone," says Schneider. This solution is also not cheap and would increase the price of water for everyone. "However, I realize that many people still prefer this," Schneider concluded and promised: "We will inform you of the results of our tests as soon as possible. In around six weeks, we will have the first results on measures for the pipeline network. We will need until the end of the year to examine the construction measures for a filter."