Each year the RATP drains off on average 9.75 million m³ of groundwater to avoid the flooding of its infrastructures. Most of this water is disposed of via the sewerage system (an average of 6.7 million m³ per year over the past three years). However, in the vast majority of cases, there is no obligation for this water to be treated in a sewage works and part of it is likely to flow into the natural environment (rivers, streams, canals, lakes etc.) or be used for functions that do not require the quality of drinking water.
In liaison with local authorities and stakeholders, the RATP launched the initiative to valorize the uses of its dewatering and asked Apur to analyse and map these resources and the options for using the water locally. Examination of infrastructures has enabled a database to be established which specifies the volumes and reliability levels of the dewatering stations (- postes d’épuisement - PEP) and the destination of the drained-off water: discharged into the sewers, the natural environment, the City of Paris non-drinking water network for watering and cleaning uses etc.
This unprecedented collection of maps on a territorial scale, provides a basis for identifying other potential uses in the short and medium term. Five representative categories have been selected as well as proximity criteria (100 m, 200 m, 500 m etc.) :
- Natural environment, surface water and raw water and rainwater purification systems
- Open spaces
- Large public and private property owners
- Technical services and industrial installations
- Projects sectors
Examples accompany these categories showing how this non-drinking water could be used advantageously in various different situations (water enhanced landscaping, the blue belt in parks, gardens, development of public spaces, watering, cleaning, sanitary supply, combating urban heat islands, etc.). At the same time, based of this study, Apur developed a web service tool, to exploit, update and share data. This tool is at the experimental stage and currently being tested by RATP teams and could, in the long term, improve exchanges with other players in the territory.
This work on dewatering, carried out in close collaboration with the RATP teams, opens up new perspectives in terms of adapting to climate change and integrating urban cycles. It not only addresses the flow of water between the city and natural environments but also existing infrastructures, their complementarity and decompartmentalisation. The city of tomorrow will need water for its ground surfaces, plant life, hygiene and its beauty. The use of this resource remains to be captured in a global economy specific to metropolitan contexts.
