Questions and Answers on Water Reuse

We are in fact continuously reusing water. After all, all water forms part of a large water cycle Thus water reuse in this context refers to the deliberate use of waste water in smaller water cycles as a means of alleviating regional shortages. This can take the form of the recirculation of water in industrial production processes, which is already widely practised in Germany, and of the use of reclaimed waste water for agricultural irrigation. 

For this purpose, the waste water undergoes additional processing after its conventional treatment in the sewage treatment plant (then referred to as “reclaimed water”). 

The EU regulation 2020/741 only refers to the agricultural irrigation with reclaimed water. 

Municipal waste water is defined as water that is treated according to the European Urban Waste Water Treatment Directive 91/271/EEC in municipal waste water treatment plants. This includes waste water from households, rain water (in the case of combined sewerage) and waste water from some selected industries (see Annex III to 91/271/EEC e.g. the manufacture of fruit and vegetable products and beverages).

Municipal waste water contains pathogens and nutrients, metals and chemical pollutants. If these are not removed sufficiently thoroughly from the waste water, risks to human health, soil, groundwater, plants and animals result. 

The three-stage waste water treatment process that is now standard practice in Germany has been optimised for the reduction of nutrients, which is why poorly degradable pollutants (e.g. heavy metals, polycyclic aromatic hydrocarbons (PAHs) and other organic micro-pollutants) are not fully eliminated. Bacteria are reduced in conventional waste water treatment plants by 2-3 orders of magnitude. And yet, since concentrations are very high in the intial waste water, relevant amounts of bacteria are still found in the final effluent after the three-stage waste water treatment. 

The risk from the use of reclaimed waste water therefore depends, on the one hand, to a significant extent on the treatment processes. On the other, the potential exposure of the environment and human beings plays a role - e.g. the risk to humans posed by the consumption of raw food is higher than it is in the case of cooked or processed products. The possible contamination of groundwater depends, among other things, on the soil and the climate. Studies have shown that water reuse can cause groundwater contamination (e.g. with pharmaceutical products). In the interest of sustainable groundwater and soil protection, water reuse must therefore obey the precautionary principle.

For further details on the possible risks of water reuse, see also UBA text 34/2016 (in German)..

Water reuse is practised in particular in semi-arid and arid regions.

One of the leading countries in this regard is Israel, where waste water has been recycled for further uses since the 1950s. About 75-80 percent of waste water is recycled there, meeting over half of all agricultural needs. Many years of experience in the field of water reuse for the irrigation of green spaces and agriculture as well as for groundwater recharge have also been gathered in the US, especially in California, and in Australia. In Windhoek, Namibia, waste water has been reclaimed for the purpose of drinking water provision since 1969. 

Within the EU, Spain which reuses over 500 million cubic metres of reclaimed waste water per annum is the leading country (BIO 2015). This practice is also in use in Portugal, Italy, Greece, Cyprus and France - to varying degrees and for different uses which are laid down in national laws or standards. The experience of water reuse is not confined to the Mediterranean Member States. For example, 2.5 million cubic metres of extensively reclaimed waste water are used in Torreele, Belgium, each year for groundwater recharge for indirect drinking water production.

To prevent existing risks to the environment and human and animal health, international (e.g. ISO 16075) and national regulations (e.g. US EPA 2012;) NHMRC 2006) are in place. Within the EU, the six Member States mentioned above have thus far adopted legal provisions for water reuse. 

In Germany, only a very low percentage of the total volume of water extracted is used for agricultural irrigation . In 2016, an analysis of the current and future requirements for irrigation has come to the conclusion that there is no nationwide need for the use of reclaimed water (UBA text 34/2016). However, following the droughts in previous years we see an increasing demand in irrigation water including reclaimed water. The funding measures WavE and WavE II focus on potential water reuse applications in Germany.

Treated municipal waste water has been used at two locations in Germany. This practice has historical roots in Wolfsburg and Braunschweig. In Braunschweig treated waste water from the treatment plant at Steinhof has been used for irrigating agricultural land as well as for groundwater recharge (Abwasserverband Braunschweig). Also, in Wolfsburg, nutrient-rich treated waste water had been used for irrigation in summer, and, in winter, water with a low nutrient content had been used for groundwater recharge (Wolfsburger Entwässerungsbetriebe). At both locations, the cultivation of fruit and vegetables for raw consumption is prohibited. In contrast to the EU regulation, water treatment in Braunschweig and Wolfsburg had previously not included disinfection or filtration measures. The practice at both sites is being adapted according to the new legislation.

The Lower Saxon Department for Water, Coastal and Nature Conservation found pharmaceutical residues drugs or X-ray contrast agents in the groundwater under the irrigated areas.

The quality of irrigation water in the EU differs according to the water sources and the prevailing pressures. There are no EU-wide regulations for irrigation water and no record of the qualities of the used irrigation water. 

Where water for irrigation is extracted from surface waters, the impact of discharges from sewage treatment plants plays an essential role. 

In dependence on the proportion of waste water and the technology used in waste water treatment plants, rivers and canals can be affected by pathogens and pollutants.  

According to a study by TU Munich (2017), European rivers which contain 10% of treated waste water from sewage treatment plants with a secondary treatment process (compliance with EU Urban Waste Water Directive 91/271/EEC) have high concentrations of pathogens that significantly exceed the requirements defined in the aforementioned EU guidelines on microbiological risks (see 2 above). The requirements of the Commission proposal for a regulation on water reuse for classes A and B would also not be met. 

This shows that further treatment and risk management are also necessary for irrigation from “conventional” sources. 

In Germany, (non-legally-binding) DIN standards for tolerances for different metals and semimetals in irrigation water (DIN 19684-10) and requirements for hygienic concerns about irrigation water (DIN 19650) are in place. The latter distinguishes between various suitability classes in accordance with the intended application.