Rainwater harvesting serves a dual function as a means of drainage and as a means of water supply. As a result, it has fallen in a no-man’s-land of lost opportunity, not fully the interest of Local Authorities, the Environment Agency, central Government or Water Companies.
Rainwater harvesting doesn’t just save water – it prevents flooding, increases sewer capacity and, by limiting surface water runoff, helps reduce pollution in the water environment. In our policy-making, we must break down the silos in our thinking. There’s no one single bullet. A range of measures will be necessary to enable the full potential of rainwater reuse if we are to avoid water shortages.
1. Embrace Digital Technologies to Improve Cost-Benefits
New digital technologies have made it practical and cost-effective to use a single tank for both rainwater harvesting and surface water drainage. SDS Intellistorm® uses weather prediction data to manage tank levels automatically, so that they have the capacity to accept water when it starts to rain heavily. Such systems are making cost-benefit justifications significantly more attractive, especially for commercial and community-level residential schemes. Our policy making, and accepted design guidance, needs to take full regard of the availability of these technologies to ensure future-proof standards and regulations.
2. Make Water Metering Compulsory
Introducing compulsory water metering for all domestic households would encourage more people to see the true value – and cost – of water. This would go a long way to changing perceptions around water reuse. Wherever mains water is provided as an unlimited resource, there can be no in-built incentive to consumers, or to businesses, that encourages water-saving.
3. Discount Surface Water Charges for Consumers
There is no consistent and automatic mechanism for Water Companies to reward homeowners for reducing their surface water discharges, except where they demonstrate a 100% disconnection. This does nothing to encourage rainwater harvesting schemes which attenuate rainwater at source, but still rely on a managed, although much reduced, discharge at times of peak rainfall.
Since the early 2000s, householders in Germany have been entitled to a discount on their property taxes and surface water charges, which is broadly proportionate to the reduction in the volume of water entering the sewer. This system has incentivised both an increase in the use of property-level permeable surface features and SuDS, as well as a marked uptake in the installation of rainwater harvesting systems.
4. Change Building Regulations
Since the abandonment of the Code for Sustainable Homes five years ago, water efficiency for new residential developments has been governed by the Building Regulations (part G) standard of 125 litres per person per day with an optional requirement of 110 litres per day through local planning policies. Some people argue that making 110 litres or even 100 litres the general standard is needed to accelerate water efficiency in the UK and prevent future shortages.
5. Incentivise Developers Through Infrastructure Charges
Ever since the recommendations of the 2008 Pitt Review, arguments have been made to remove the developer’s automatic right to connect to the public sewer. However, this approach has been strongly resisted by housebuilders. A carrot-rather-than-stick approach looks more promising and some Water Companies have trialled incentives that discount the water and sewerage infrastructure charges developers pay to connect to the network if they can demonstrate water efficiency measures and/or incorporate SuDS to reduce the surface water load on sewers. Further work by Water UK, Water Companies and OFWAT to encourage such schemes can be a significant driver for water efficiency and rainwater harvesting.
6. Insist on Water Reuse as First in the Suds Hierarchy
In the hierarchy used by drainage engineers to design SuDS schemes, re-using rainwater is the number one priority. This is advised in the SuDS design bible, CIRIA 753 The SuDS Manual. However, many Local Authority, Water Company guidance and indeed English Planning Practice Guidance (PPG) for SuDS overlooks reuse and encourages designers to consider infiltration as the first option.
In London, where the London Plan already places rainwater harvesting at number one in the hierarchy, more rainwater harvesting schemes are beginning to emerge, including at some prestigious commercial developments.
If using rainwater as a resource is a priority in best-practice SuDS design, then let’s make sure it informs any changes in policy.
7. Reinstate “Schedule 3”
In Wales, rainwater reuse is first in the design hierarchy through its statutory technical standards for SuDS, supporting Schedule 3 of the Flood and Water Management Act. In England, Schedule 3 was abandoned in favour of regulating SuDS on new developments through National Planning Policy Framework. Some people hope that the experience in Wales will prove the value of the original approach and persuade this, or future, Governments to reverse the decision.
8. Revise Non-Statutory Technical Standards for SuDS in England
In England, the Non-Statutory Technical Standards for SuDS make no mention of water saving, nor does the corresponding Planning Practice Guidance which begins with discharging surface water to ground through infiltration. Rainwater harvesting must be fully considered as part of the standards that guide planning authorities in how to deliver best-practice SuDS designs in their areas.
A review of the standards is currently underway and a survey, organised through CIRIA, closed on 25 June.
9. Introduce a Residential Property Resilience Certificate
The BREEAM sustainability assessment scheme has become an important driver for encouraging rainwater harvesting and other water efficiency measures in commercial buildings. Landlords see an ‘Excellent’ or ‘Outstanding’ rating for their properties as an attraction for potential tenants. Rainwater and greywater schemes help them to meet the standards.
The Westminster Sustainable Business Forum is among influential groups lobbying for a similar Property Resilience Certificate as part of the proposed Future Homes Standard. It has the potential to become a driver to include SuDS with rainwater harvesting on domestic schemes.
10. Compulsory Building Regulations
One way to guarantee the inclusion of rainwater harvesting schemes on new developments is to make them compulsory on new properties as part of building regulations. Viewed in isolation, this requirement might be resisted as too much of a cost burden for affordable housing. However, schemes could be made feasible through imaginative partnership working with Water Companies and Local Authorities on community-level schemes that also deliver multiple benefits through SuDS.
Whether installed in a single property, street, community scheme or commercial building, rainwater harvesting systems have the potential to make a huge contribution to the UK’s water-saving efforts. Retrofitted in existing properties, or included in new developments, there’s so much more to be done to exploit their full potential.