Water Reuse

Water reuse enables circular water use, it fosters further elimination of pollutants and pathogens and can contribute to a reduction of freshwater usage and wastewater discharge. 

In Germany the recirculation of water is especially practiced in industrial sectors as e.g. paper production. Some EU member states, mostly in the Mediterranean, irrigate agricultural land with reclaimed water originating from urban wastewater. According to the European Commission’s „Blueprint to Safeguard Europe's Water Resources“ (2012) there is still significant potential to extend water reuse in response to climate change and water scarcity but a lack of common requirements prevents widespread uptake.

In response to that the European Circular Economy Action Plan defined actions to promote water reuse. This included “Guidelines on Integrating Water Reuse into Water Planning and Management in the context of the WFD” (published 2016) and a legislative proposal  on common minimum requirements for water reuse for agricultural irrigation and aquifer recharge (published 2018). Since 26 June 2023 the  Regulation on minimum requirements for water reuse for agricultural irrigation applies in all EU member states.

In Germany we are only using 11.4 % of the 188 billion cubic metres of renewable water resources that are available. With 2.2 % of the total water abstractions (0.4 billion cubic metres) agricultural irrigation is comparable low in water demand (data from 2019) but nevertheless higher than in previous years. The area of irrigated fields has increased by 36% from 2009 to 2019. Due to climatic changes the agricultural irrigation demand can increase regionally and may exceed the natural groundwater recharge.

This can already be seen in some regions of Germany (see „Trockenheit in Deutschland – Fragen und Antworten“/ only in German).

2016 UBA has published a study on framework conditions for an environmentally friendly use of reclaimed water for agricultural irrigation (for an English summary see page 10 of the Study Report).

Water reuse for agricultural irrigation poses potential risks for human health, soils and groundwater. In conventional wastewater treatment processes pathogens and pollutants are not fully eliminated. That long-term irrigation with conventionally treated wastewater may introduce micropollutants to the environment can be seen in the regions of Braunschweig and Wolfsburg. There, traces of pharmaceutical substances and x-ray contrast agents were detected in the groundwater (study results only in German). Advanced wastewater treatment and demand-based irrigation are crucial to limit the spread of pathogens and contaminants including micropollutants (e.g. substances from pharmaceuticals, pesticides). Soil properties, hydrogeology, farming and irrigation practices further influence the potential risks for humans and the environment. These aspects shall be addresses in a site-specific risk assessment which is also prescribed by the EU regulation 2020/741 on water reuse.

Potential risks can also arise from “indirect water reuse” (or “de facto reuse”) for example when surface water that contains large shares of treated wastewater effluents are used for agricultural irrigation or drinking water supply through bank filtration. For irrigation from surface waters there are no binding quality standards – in theory, pathogens and pollutants can be spread to agricultural fields. High contributions of wastewater effluents to German rivers can especially occur in phases of low-flow conditions. This has been shown by a UBA study published in 2018 (for an English article see Karakurt et al. 2019).

There is a growing number of studies on potential uses, risks and necessary quality requirements of water reuse, including projects funded by the Federal Ministry of Education and Research. The recent funding measure “Future-oriented Technologies and Concepts to Increase Water Availability by Water Reuse and Desalination – WavE” included three projects related to the use of reclaimed urban wastewater (TrinkWave MULTI-ReUse and HypoWave). UBA was involved in TrinkWave. In a second phase of the funding measure WavE II (Water Technologies: Water Reuse” 2021-2024), UBA participates with the project PU2R „Point-of-Use Re-Use: Dezentrale landwirtschaftliche Wiederverwendung von häuslichem Abwasser zur Verringerung von Nutzungskonkurrenzen“ (Decentralized agricultural reuse of municipal wastewater to reduce competition for water) and „FITWAS - Wiederverwendung von Filterspülwässern aus der Grundwasseraufbereitung zur Sicherung der Trinkwasserversorgung“ (Reusing rinsing water from groundwater reclamation to secure drinking water supply). Other WavE II projects include FlexTreat and Nutzwasser that are also dealing with water reuse in agriculture.