Guidance

Supplementary guidance: drainage and wastewater management plans for storm overflows

Updated 26 August 2022

Applies to England and Wales

In February 2022 the government published the Guiding principles for drainage and wastewater management plans. The government committed to providing supplementary guidance for companies on the ambition for storm overflows.

This Storm Overflows Discharge Reduction Plan sets out clearly the pace and scale of action required by water companies to protect people and the environment and meet acceptable usage of storm overflows.

We expect water and sewerage companies in England to meet the targets in the Storm Overflows Discharge Reduction Plan, and set out how they will achieve these reductions in their drainage and wastewater management plans.

Targets for water companies

Protecting the environment

Headline target: Water companies will only be permitted to discharge from a storm overflow where they can demonstrate that there is no local adverse ecological impact.

Sub-targets

1. The headline target must be achieved for most (at least 75%) of storm overflows discharging in or close to high priority sites (as defined in Annex 1 of the Storm Overflows Discharge Reduction Plan) by 2035.

2. It must be achieved for all (100%) storm overflows discharging in or close to high priority sites by 2045.

3. Water companies must achieve this target for all remaining storm overflows sites by 2050.

What will these targets achieve?

This target will ensure storm overflows are only permitted to discharge where water companies can demonstrate there is no local adverse ecological impact. This target will ensure that no water body in England should fail to achieve good ecological status due to storm overflow discharges.

The target ensures there is no wider local impact, rather than just considering the impact at a sampling point which can be far away from a storm overflow as has been done in the past. The local impact will be assessed by water quality monitors near the overflows. This target protects biodiversity at both a local and national scale and will result in the complete elimination of ecological harm from storm overflows.

The sub-targets outline specific milestones for companies. This will help government and regulators assess progress in line with the Storm Overflow Discharge Reduction Plan’s expectations at each subsequent review point.

Protecting public health in designated bathing waters

Headline Target: Water companies must significantly reduce harmful pathogens from storm overflows discharging into and near designated bathing waters, by either: applying disinfection; or reducing the frequency of discharges to meet Environment Agency spill standards by 2035.

What will this target achieve?

This target will address the harm to human health from storm overflow discharges in designated bathing waters, where people are most likely to use water bodies for recreation. This target applies to both inland and coastal areas. It will require all storm overflows near to existing, or any newly designated, bathing areas to comply with a rigorous standard for bathing, which sets a limit of 3 or fewer discharges per bathing season, with some bathing waters having tighter limits.

8% of overflows are close to designated bathing waters. We expect this target to reduce discharges from overflows close to designated bathing waters by over 70% during the bathing season and for reductions to also occur outside of the bathing season.

These first 2 targets (ecology and public health) and their sub-targets will ensure that the overflows causing the most harm, to public health or the environment, are addressed first.

This target will also be supported by the government’s work to promote the designation of more bathing waters and rivers, and ensure that users are informed in near-real time of any overflow activity or impacts on water quality in bathing waters.

Achieving the targets

Water companies will need to look for the best value solutions for people and the environment to achieve the targets at a local level.

Water companies must plan to achieve all relevant targets when developing solutions. For example, where analysis shows that the ecological harm can be eliminated but storm overflows are still being used too frequently, both the environmental and rainfall targets should be achieved.

The government also expects water companies to adhere to the following principles when achieving the targets: 

Complying with regulations

1. Water companies must comply with all their existing regulatory obligations and duties, including permits issued by the Environment Agency.

Water companies need to maintain and upgrade their wastewater systems to ensure they meet their statutory service obligations and keep pace with all the pressures that add surface water to the combined sewer network. Before implementing infrastructure upgrades, water companies must ensure all their wastewater and drainage assets are working as intended, are not limiting capacity of their sewage system, and are compliant with all relevant legislation and permits. This includes (but is not limited to) proactive management and adequate maintenance of assets, with timely replacements, upgrades, or repairs of assets as appropriate. Upgrades as a result of non-compliance do not fall within the scope of this plan.

If water companies are found not to comply with their legal responsibilities, Ofwat and the Environment Agency can take robust action. This may result in, for example:

• fines for water companies responsible for serious and deliberate pollution incidents, to be taken from water company profits
• potential prison sentences following successful prosecution for Chief Executives and Board members whose companies are responsible for the most serious incidents

Planning and forward look

2. The government expects water companies to have maps of their sewer networks upstream of overflows, and understand where properties with separate rainwater pipes are connected to their combined sewer network.

3. Water companies will clearly set out how they will meet their storm overflow targets in their drainage and wastewater management plans.

4. In developing the best solutions, water companies should base their decisions on robust evidence and explore ways in which they can maximise wider benefits where solutions can address multiple issues, delivering best value for people and the environment.

The requirements on water companies to undertake comprehensive long-term planning with regards to the capacity and resilience of the sewage network shall form part of water companies’ Drainage and Wastewater Management Plan objectives. Proper planning and mapping will enable water companies to act when separation of surface water is the best solution to achieve sustainable reductions in sewage discharges. Water companies must prioritise removing existing surface water connections from the combined sewer network over building additional storage, wherever this achieves the best outcome for people and the environment.  

Drainage and wastewater management plans allow water companies to deliver the storm overflow targets in an integrated way. Water companies will be required to clearly set out how they will meet their storm overflow targets in these plans. Given the importance of the local context, water companies will work closely with local partners, such as local councils, highway authorities, drainage asset owners and managers, to ensure that their plans strategically link to other local plans, such as local flood risk management strategies. Projects proposed as a result of drainage and wastewater management plans will be reviewed by the Environment Agency and Ofwat as part of the business planning process. The Environment Act 2021 allows the drainage and wastewater management plans to be made statutory. The government will implement the relevant provisions during the next Drainage and Wastewater Management planning cycle (2023 to 2028).

Driving better solutions

5. We expect water companies to achieve year on year reductions in the amount of surface water that is connected to their combined sewer network.

Water companies must remove rainwater from the combined sewer system as part of effectually draining their areas. This should include limiting any new connections of surface water to the combined sewer network, and any new connections should be offset by disconnecting a greater volume of surface water elsewhere within the network. 

6. We expect water companies to prioritise a natural capital approach, considering carbon reduction and biodiversity net gain, as well as catchment-level and nature-based solutions in their planning.

Traditional solutions to reduce discharges, such as increasing storage capacity, are carbon intensive. The costs and benefits of such interventions must be considered in decision-making. Solutions should be effective over the long-term and account for future pressures. 

Green infrastructure and other nature-based solutions are an effective option to reduce the harm caused by storm overflows and can provide multiple co-benefits for the environment and society. For example, separating surface water so that it doesn’t mix with sewage and is diverted to water gardens or wetlands improves water quality, creates new habitats for species and acts as a carbon sink.

In addition to the targets on storm overflows set out in this Plan, the government has committed to halt the decline in species abundance by 2030 in the Environment Act, and committed to net zero by 2050 in the Climate Change Act. The government has also committed to raise at least £500 million in private finance for nature’s recovery every year by 2027 and more than £1 billion a year by 2030. These objectives, focussed on protecting our natural environment must be approached in a cohesive way. The Environment Agency and Ofwat will actively encourage companies to consider green infrastructure in their proposals to achieve the targets set out in this plan, and wider government priorities set out in the government’s strategic policy statement to Ofwat. As set out in our strategic policy statement to Ofwat, we expect companies to operate in partnerships across catchments maximising co-funding and green finance opportunities, wherever appropriate, including through market mechanisms.

We are aware that green infrastructure enhancements often have longer delivery timelines than traditional concrete solutions and may therefore be seen as riskier investments by water companies. For that reason, the Environment Agency and Ofwat will work to ensure assessment processes promote and incentivise the use of nature-based solution in favour of more carbon intensive alternatives.

To promote sustainable solutions, green infrastructure projects started before 2027 and delivered as quickly as possible will count towards completion of the targets. This will be the case even when the full environmental impact of these projects has not yet been realised by the target end date.

7. We expect water companies to consider treatment of sewage discharges as an alternative solution where appropriate.

Water companies need to significantly reduce their untreated sewage discharges from storm overflows. In some cases, it may be better to treat discharges, rather than to reduce their frequency. In these instances, water companies may consider treatment of sewage discharges as an alternative way to eliminate public harm, rather than reducing their frequency. For example, this may be the case for highly diluted overflow discharges caused by groundwater infiltrating pipes which are difficult to repair. Where treatment is used, there will be checks to ensure compliance with the required standards.

Better management of our rainwater by water companies

We will expect water companies to value rainwater as a resource which benefits people and the environment, and to protect the natural water cycles that maintain biodiversity and full flowing rivers. Rainwater should be managed following these 2 principles:

8. Rainwater should be treated as a resource to be valued for the benefit of people and the environment, not mixed with sewage or other contaminants.

9. Rainwater should be discharged back to the environment as close as possible to where it lands or channelled to a close watercourse without first mixing it with sewage.

Water companies should prevent additional rainwater from entering the combined sewer network and remove existing rainwater connections where it is the best value solution.