Decentralised water reuse as a building block of municipal resilience
Why centralised systems become more resilient through decentralised componentsMunicipal water supply and wastewater disposal are critical infrastructure. In addition to climate risks, physical and digital threats are becoming increasingly important. Decentralised solutions such as rainwater harvesting and water reuse are not a substitute, but a resilience-oriented addition to the central infrastructure.
Why resilience needs to be considered now
Municipal drinking water supply and wastewater disposal ensure basic services of general interest and must function reliably even in the event of disruptions. In the KRITIS water sector, this includes drinking water supply (extraction, treatment, distribution) as well as wastewater disposal, wastewater treatment, urban drainage and the control and monitoring of these systems. At the same time, physical and digital risks are becoming more of a focus. The EU has defined minimum requirements and supervision to strengthen the resilience of critical facilities; the protection of critical infrastructure is also being further tightened in Germany.
What the water industry can learn from the energy supply sector
Resilience has been a guiding principle in the energy supply sector for years (redundancy, island operation, decentralised feeders). The same principle applies to the water industry: the greater the dependency on a few centralised nodes, the greater the system vulnerability - and the more important it is to have supplements that distribute loads and create local reserves.
Security and crisis reference:
Decentralised systems as redundancy against failuresThe security situation in Europe has accelerated the debate about the protection and functionality of critical infrastructures. For local authorities, the question of how quickly supply and disposal can be stabilised after disruptions - and to what extent individual failures can have an impact - is therefore becoming increasingly important.
Decentralised systems contribute to this if they are integrated correctly in terms of planning and operation. They do not replace municipal responsibility, but expand the range of instruments - similar to emergency power, redundant pumping stations or additional storage volumes.
Contribution of decentralised systems to resilience
- Risk diversification: Several local units reduce dependency on individual centralised components.
- Emergency operation capability for partial functions: Non-drinking water-related applications can be backed up locally (e.g. process water, irrigation, toilet flushing).
- Operational transparency: Measuring and monitoring concepts support safe operation - especially with defined hygiene and quality requirements.
Rainwater management and sponge city: relief instead of expansion
In addition to the safety aspect, heavy rainfall, overloading of the drainage system and urban heat remain key municipal risks. Decentralised rainwater management (retention, infiltration, use) works where the pollution occurs - on the property and in the neighbourhood.
Sponge city approaches aim to retain, evaporate and infiltrate rainwater in a targeted manner. This can reduce runoff peaks, minimise substance inputs and support groundwater recharge - and at the same time contribute to cooling the urban climate through evaporation.
Traditional grid expansion tends to solve symptoms "downstream". Decentralised measures start "upstream" and can - depending on the local situation - postpone, reduce or target expansion. This often results in a practicable combination: central infrastructure remains the backbone, decentralised measures are systematically implemented as a second level.
From competition to cooperation
Implementation models for municipalities
- Neighbourhood solutions instead of individual systems (scaling, uniform operation)
- Operator/contracting models (maintenance, monitoring, responsibilities regulated)
- Incentive systems in the rainwater sector (e.g. via retention or runoff effect) - as part of local bylaws and fee calculation
- Pilot programmes with measurable targets (relief effect, volume, operating experience)
Conclusion
Decentralised water reuse and rainwater management are not an alternative to municipal infrastructure, but a necessary, resilience-oriented addition - technically, organisationally and increasingly also strategically.
One example of an integrative overall solution is the Aachen research and development alliance AIX-Net-WWR, which brings together centralised and decentralised components in an overall system.