Decision Support for Rainwater and Stormwater Harvesting

When is it sustainable to recycle rainwater and stormwater, and according to whom? And is it appropriate to flush toilets or water lawns with clean drinking water?

Rainwater from roofs, as well as stormwater in general, is technically water that could be utilised on a larger scale and for various purposes, and different systems are available on the market. Increased rainwater harvesting could also mean that capacity-enhancing measures in stormwater systems can be postponed. Reducing the load on drinking water and stormwater networks can be a major benefit for water utilities, but it often falls outside their mandate and control, as property owners must bear the costs and efforts involved.

The project has examined the reuse of rainwater and stormwater by analysing technical, social, environmental and economic aspects. It was carried out as an SVU project led by Tyréns, with LBVA, VA SYD, Sweden Water Research and Sweco participating and contributing case studies and experience from previous recirculation projects.

Purpose and Method

The aim of the project was to further develop and apply multi-criteria analysis (MCA) as a decision-support tool for stormwater use by comparing different reuse systems with traditional drinking water supply and stormwater management. This was done in three case studies where alternative recirculation solutions were compared based on sustainability criteria. Scoring and weighting of criteria were carried out by representatives from water utilities, property owners, consultants and researchers.

Results

The project has resulted in an SVU report (Decision Support for Stormwater Reuse – Guidance for Multi-Criteria Analysis, report number 2025-20), which is now published and can be used as guidance in planning and decision-making regarding stormwater reuse. The main findings of the report can be summarised as follows:

• The MCA methodology proved to be a useful tool for structuring complex decisions on the reuse of rainwater and stormwater, particularly when several stakeholders with different goals and perspectives are involved.
• By involving different stakeholder groups in scoring and weighting, a shared understanding and dialogue was created on how technical, social, environmental and economic aspects should be valued when choosing a solution.
• Experience shows that tools based on MCA do not automatically provide a ready-made decision, but they create the conditions for well-balanced decisions by highlighting the strengths and weaknesses of different alternatives.
• The report also includes suggestions for criteria and scoring methods that can be applied in similar projects and in future planning processes.

The report is an important resource for water utilities, urban planners and property owners who wish to assess when the reuse of rainwater and stormwater is a sustainable alternative to traditional water supply. Download the report (in swedish, short english summary) as pdf.

Project manager: Johan Kjellin, Tyréns, johan.kjellin@tyrens.se