New Policy Brief: Collective & Scalable Strategies for Non-Conventional Water Resources

par | Juin 4, 2026 | Belgium CS, Notes d'orientation

Collective Rainwater Management in Flanders

Flanders faces growing water stress, prompting increasing interest in decentralised, circular water management solutions, such as buffering and reusing rainwater locally or recharging groundwater. However, the business case for these solutions is often unclear, hindering investment. This RETOUCH NEXUS policy brief applies a full cost-benefit analysis (CBA) to a greenfield business park in Flanders, comparing individual rainwater systems against a collective solution over a 40-year horizon. The results reveal a clear economic and ecological advantage for collective approaches, and offer a replicable framework for scaling this evidence across Flanders and similar European contexts.

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Messages clés

1

Collective systems are more cost-effective than individual ones: A 40-year CBA at the Keiberg Vossem business park shows a net saving of €242,808 for a collective rainwater system compared to individual tanks. Shared infrastructure reduces per-unit investment and operational costs while increasing total volumes captured and reused.

2

Multi-benefit analysis is essential to make the business case visible: Benefits span drinking water savings (€0.59/m³), wastewater treatment avoidance (€0.30/m³), and groundwater-related costs (€0.40/m³). A standard single-sector analysis misses most of the value. Integrating a water balance module with avoided-cost valuation reveals the full picture.

3

Surplus rainwater generates critical WEFE co-benefits: Rainwater that cannot be used on-site can be directed to groundwater recharge, supporting local ecosystems and agricultural water availability during dry periods. These cross-sectoral benefits, reduced energy for treatment, ecosystem support, agricultural resilience, must be recognised in policy frameworks to justify collective investment.

4

Governance and contractual frameworks are needed to enable collective management: Multi-actor coordination between businesses, municipalities, water utilities (De Watergroep), and research partners is required. Contractual arrangements for collective rainwater trading and distribution, supported by the Flemish Blue Deal framework, provide a concrete governance pathway.

5

The CBA methodology is directly replicable across Flanders and beyond: The core framework, water balance combined with avoided-cost valuation, can be applied to other business parks, industrial zones, and residential areas. Scaling up to a regional programme under the Flemish Blue Deal, with standardised incentive structures and cost-sharing models, represents the next step.