Treated-wastewater reuse: what water reuse changes

As droughts multiply, reusing water already abstracted rather than pumping new water becomes obvious. Treated-wastewater reuse (known in France as REUT) means giving a second life to the purified water leaving a wastewater-treatment plant, for non-potable uses.

Long under-developed in France (less than 1% of treated wastewater is reused there, far from the Mediterranean leaders), reuse is now regulated by recent European and French texts. Here is the breakdown.

1. What is water reuse?

Treated-wastewater reuse means re-employing the purified water leaving a treatment plant (STEP), after possible additional treatment, for a use that does not require potable water: irrigation, cleaning, watering, certain industrial uses.

The aim is twofold: reduce pressure on resources (groundwater, rivers) and secure supply during restrictions. It is a major building block of water frugality.

2. The regulatory framework: Europe and France

Two texts structure reuse:

• Regulation (EU) 2020/741 of 25 May 2020, applicable since 26 June 2023: it sets minimum requirements for quality and risk management for water reuse, primarily for agricultural irrigation.
• Decree No. 2023-835 of 29 August 2023 (France): it defines the conditions for using treated wastewater and rainwater for non-domestic uses, and sets the authorisation procedure for reuse projects.

Every project therefore requires an authorisation and a risk-management plan, tailored to the intended use.

3. The 4 quality classes (A to D)

The European regulation defines four quality classes of recycled water, from the most demanding (A) to the least demanding (D), according to the type of crop and irrigation method:

Each class has its own thresholds (E. coli, BOD₅, TSS, turbidity) and monitoring measures: the more the use is in contact with food, the higher the required quality.

4. Authorised and prohibited uses

The golden rule: reused water is never intended for human consumption, and the use must be compatible with the quality class produced.

5. The reuse treatment chain

Requalifying purified water for a new use relies on a multi-barrier logic, downstream of the plant:

• Advanced filtration: media filtration or membrane (ultrafiltration) to remove TSS and micro-organisms.
• Disinfection: UV and/or chlorination to control the bacterial load.
• Monitoring: continuous monitoring (turbidity, disinfection) and a control plan.

The treatment level is sized according to the quality class required by the use: the stricter the class (A), the more the chain combines fine filtration, UV disinfection and sometimes reverse osmosis.

6. And in Belgium and the Netherlands?

Regulation (EU) 2020/741 applies across the whole Union. In Belgium, water management falls to the Regions (Flanders, Wallonia, Brussels), with growing pressure on reuse, particularly in Flanders where summer water stress is marked. The European base remains common; the arrangements are set out at regional level. In the Netherlands, a country very advanced in water management, the subject is also a priority (waterschappen, Rijkswaterstaat): DIMM has a significant share of its customers there, alongside Belgium and France.

7. Who is reuse for?

Reuse is of particular interest to farmers and cooperatives in stressed areas, water-intensive industries, communities (watering, roads), golf courses and green spaces, or laundries. The return on investment is all the faster where the resource is scarce and water is expensive.

Conclusion

Reuse is no longer a curiosity: it is a regulated solution, now with a clear European and French framework. Well sized — filtration, disinfection, monitoring, according to the quality class — it turns a constraint (water shortage) into a controlled resource. The starting point remains analysing the intended use and the available water.

The DIMM teams support partner installers, distributors and resellers, in Belgium, France and the Netherlands, in choosing and sizing treatment solutions for water reuse.