WFlushing the toilet in the Ökohaus at Frankfurt’s Westbahnhof does not use up any valuable resources. No drinking water flows out of the cistern, but so-called service or process water – collected rainwater and contaminated groundwater that is not suitable for food. According to Gerd Heinemann, the managing director of the owner company, the system has proven itself since the building was completed in 1992. This could save around four million liters of drinking water every year. An aspect that has gained in importance due to the recent drought summer and the ongoing population growth.
If environmentalists have their way, there will be separate pipe systems for drinking and service water in all new buildings in the future. Wolf-Rüdiger Hansen from the district board of the BUND presented this request to the planning committee of the city parliament this week. Frankfurt draws too much water from the Vogelsberg, which causes ecological problems there. Resources can be conserved by using water for the toilet, watering the garden and washing machine instead, which comes from rainfall, rivers or the treated wastewater from showers and sinks. The conservationists are calling for the obligation to use service water to be stipulated in development plans – but according to a spokesman for the planning department, there is no legal basis for this.
39 liters less per person per day
In principle, up to a third of the drinking water can be saved by using process water in private households. This is the result of a study published on Thursday by the Frankfurt Institute for Social-Ecological Research on behalf of the water procurement company Hessenwasser. The average consumption of around 118 liters per person per day could be reduced by 39 liters.
However, this requires investments in the pipeline network. The extent of the impact on overall consumption in the city depends on this. If you only rely on a service water supply that can be implemented without great effort, the savings potential of 500,000 cubic meters per year is comparatively low. With greater efforts, between 5.5 million and 6.6 million cubic meters could be saved annually. A total of around 54 million cubic meters are currently consumed in Frankfurt every year.
“Theoretically, it is possible to replace the forecast increase in demand for drinking water by 2050 with service water,” says Engelbert Schramm, one of the authors of the study. Co-author Martin Zimmermann says: “The city of Frankfurt must break new ground in the drinking water supply, also in order to keep the pressure on the water resources in the surrounding area as low as possible.”
Drinking water should continue to flow from the taps. According to environmentalists, however, rainwater is sufficient to flush the toilet.
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Image: Wolfgang Eilmes
Independent of the drinking water supplier
The scientists have calculated the savings potential using the example of the Heimatsiedlung in Sachsenhausen and the planned (but currently on hold) new development area Günthersburghöfe in the north end. It becomes clear that because of the additional lines, the infrastructure costs are significantly higher than with a conventional water supply. Savings can only be achieved in the new development area and only through the use of Main water. For all other variants, the costs are significantly higher. In the home settlement, water costs would sometimes more than double. Above all, the necessary investments in double line systems have an effect. “A decision for or against a service water supply should not be made solely on the basis of cost considerations,” says the study.
The costs are one reason why the use of process water in Frankfurt’s own pipe systems has not been widespread up to now. From an operational point of view, Fraport AG has had positive experiences in Terminal 2 and in properties in the south of the airport, which are supplied with collected rainwater, among other things. Jürgen Scheuring, who manages the operation of the supply and disposal systems, also emphasizes: “It is difficult to present the topic economically.” Fraport uses the system to make itself independent of the drinking water supplier and to make a contribution to the conservation of resources.
Well water for toilet flushing
In residential construction, the municipal ABG Holding is testing the use of slightly polluted wastewater as service water in a house in Bockenheim. results are pending. As early as 1999, the GWH housing association installed its own service water pipes in a new building in the Deutschherrenviertel. “The experience with it, however, was mixed,” says the company. The very mineral-rich residues in the water meant that cisterns and sanitary ceramics got dirty extremely quickly and were difficult to maintain. Pipes and valves were also heavily stressed by the process water. In 2007, the service water pipes were shut down at the insistence of the residents.
In another building complex, on the other hand, well water is still used to flush the toilets. There, however, toilets would be used that are more suitable for operation with service water. However, the GWH refers to the high costs of double pipe installations. “So far, it has hardly been feasible from an economic point of view.”
The Hessenwasser company relies on a different form of industrial water use. Since 1959, water has been taken from the Main in Niederrad and treated so that it can then seep away into the city forest. Via the detour of the groundwater and the waterworks, it ends up in the drinking water pipes. Expensive double lines are not necessary with this method.
