The case for a national rainwater strategy: managing rainfall where it falls

20 May 2025

Rain is both a flood risk and a vital water resource – yet current policy treats it as either problem or afterthought. A joined-up national strategy is overdue

The rhythmic drumming of rain on our roofs and pavements has long been a familiar soundscape of the United Kingdom.

Yet our approach to managing this ubiquitous element has remained stubbornly fragmented, often viewing it as either a nuisance to be drained away or a resource considered only within the confines of centralised water management plans. This siloed perspective is no longer fit for purpose in an era defined by increasing climate volatility and mounting pressures on our water infrastructure.

It's time for a paradigm shift: a national rainwater management strategy that recognises the inherent potential of rainwater as both a valuable resource and a crucial element in mitigating flood risk, managed effectively right where it falls.

Asset or liability?

Currently, national strategies treat rain disparately: it is considered an asset in water resource management and a liability in flood risk management. This segregation leads to inefficiencies and missed opportunities, focusing on centralised assets and responsibilities rather than embracing a distributed and local approach.

The consequences of this binary approach are becoming increasingly apparent. We face the dual challenges of escalating surface water flood risk – with nearly 1.8 million properties at high risk by the mid-21st century – and growing water stress, particularly in densely populated areas. The summer drought of 2022 starkly illustrated how rapidly the UK can move from relative water comfort to significant pressure.

The traditional response to managing surface water runoff has relied heavily on directing it into combined sewer systems, a practice that exacerbates the issue of storm overflow discharges and strains the capacity of our wastewater treatment infrastructure.

When sewer capacity is challenged, the current approach often involves constructing large, energy-intensive storage tanks, a symptomatic "end-of-pipe" solution that fails to address the root cause. This reliance on centralised, grey infrastructure is not only environmentally costly but also overlooks the significant potential of managing rainwater at its source.

Sustainable drainage: the enabler

A more sustainable and forward-thinking approach lies in embracing the principles of sustainable drainage systems (SuDS). These encompass a wide array of techniques designed to capture, store, infiltrate, attenuate and convey surface water runoff in a way that mimics natural processes.

These nature-based solutions, ranging from swales and filter strips to permeable pavements and green roofs, offer a multitude of benefits beyond just drainage. They can enhance water quality through natural filtration, mitigate the urban heat island effect, and provide valuable amenity and biodiversity benefits. SuDS are often designed to handle significant rainfall events, offering a considerable capacity improvement over traditional highway drainage that is designed to manage rainfall events with a return period of every year or two at most.

However, the widespread adoption of SuDS at the requisite scale continues to face hurdles. While the still un-commenced Schedule 3 to the Flood and Water Management Act 2010 aimed to mandate SuDS in new development and remove the automatic right to connect surface water to public sewers, the direction for delivering remains uncertain under this government.

The current planning-led approach to encouraging SuDS has proven inadequate, suffering from inconsistent design and delivery, and a lack of clear mechanisms for adoption and long-term maintenance (see ‘To have and to hold’ in the Summer 2025 print edition, available exclusively to CIWEM members). Even apparent rules within the planning system, like the National Planning Policy Framework are open to interpretation by planners. This creates an adversarial environment where planning conditions and decisions are often challenged, causing delay and public expense.

This deficiency means new developments are often contributing unnecessarily to flood risk because they are insufficiently resilience, and are placing additional burden on water companies' drainage infrastructure. Meanwhile, developers increasingly express a willingness to work with more of a rules-based approach provided it is proportionate and enables seeking clarity and a consistent approach nationwide.

Rainwater harvesting

Alongside SuDS, rainwater harvesting and reuse present a vital opportunity to unlock the resource potential of rainfall. Capturing rainwater from rooftops and stormwater from hard surfaces can provide a reliable source of water for non-potable uses such as garden watering, toilet flushing and washing machines, and achieve significant reductions in per capita water consumption.

Furthermore, rainwater harvesting tanks can also provide crucial stormwater attenuation, especially when equipped with smart technology that allows for proactive drawdown in anticipation of rainfall events. A ‘smart SuDS’ approach can effectively bridge the gap between water resource management and flood risk mitigation at the property and development scale. But even non-smart rainwater tanks frequently used for toilet flushing will have spare capacity to store stormwater most of the time.

Regulatory review needed

Despite the clear benefits, the widespread implementation of rainwater harvesting and reuse is hampered by outdated regulations and guidance. The legal definition of "wholesome water" in the Water Industry Act 1991 currently prevents statutory water companies from providing or adopting domestic water reuse schemes for non-potable purposes.

This regulatory barrier should be urgently reviewed and updated to enable more ambitious water efficiency standards and unlock the potential of rainwater reuse. Revising Part G of the Building Regulations to require more efficient fixtures and fittings and to include an optional standard necessitating water reuse for toilet flushing would drive significant progress.

Then of course, we need clarity over whether the government is going to drive delivery of consistent quality SuDS with a clear mechanism for adoption and maintenance, either through Schedule 3 of the Flood and Water Management Act 2010 (which is currently un-implemented), the planning system or some third way.

National rainwater management strategy

To truly transform our approach to rainwater management, we need a national rainwater management strategy. This must better integrate development planning and regulation with wider water management planning and delivery. This will require collaboration across government departments, regulators, risk management authorities and local authorities. Key components of the strategy should include:

• Introducing a mandatory framework for SuDS in new developments, setting clear standards for design, delivery, adoption and maintenance. This could involve implementing Schedule 3 of the Flood and Water Management Act 2010 or exploring alternative, streamlined mandatory mechanisms that learn from the experience in Wales and potentially leverage existing frameworks for highway adoption and surface water drainage charges. But it must be mandatory.

• Making the right to connect surface water to the public sewer system conditional on first having maximised SuDS options. This fundamental shift will incentivise on-site rainwater management and reduce the burden on combined sewers.

• Ensuring that approval and adoption mechanisms apply equally to both new development and retrofitted SuDS. If we’re going to have a mechanism for new development it should also work for the ongoing maintenance of retrofit SuDS.

• Actively encouraging the integration of smart SuDS technology, such as smart rainwater harvesting tanks, within wider SuDS approaches through updated guidance and standards. This will maximise the dual benefits of water resource management and stormwater attenuation.

• Updating the legal definition of "wholesome water" to enable the widespread adoption of non-potable water reuse in homes by statutory water companies.

• Revising Part G of the Building Regulations to mandate more ambitious water efficiency standards and to encourage rainwater harvesting and greywater reuse.

By embracing a national rainwater management strategy, we can move away from treating rainwater as a mere waste product to be disposed of and instead recognise its potential as a valuable resource and a vital component of a resilient and sustainable water future.

Managing rainwater where it falls is not just a drainage solution; it's an opportunity to enhance water security, reduce flood risk, improve water quality and create more liveable and sustainable communities. The time to reimagine rain is now.

Alastair Chisholm contributed to the 'Managing rainwater where it falls: EWSC response to the Independent Water Commission', produced by the Enabling Water Smart Communities (EWSC) project.

This article originally appeared in the Summer 2025 print edition of The Environment. CIWEM members can read the issue in full (and all back issues dating back to 2016) via MyCIWEM. You can also stay up-to-date with our free monthly 'The Environment' newsletter. Subscribe here.

Alastair Chisholm is director of policy at CIWEM