The government has published supplementary guidance for water companies on drainage and wastewater management plans for storm overflows.

In February 202 the government published the Guiding principles for drainage and wastewater management plans and committed to providing supplementary guidance for companies on the ambition for storm overflows.

Introducing the guidance, the government said the 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,” the guidance says.

The guidance consists of a series of headline targets and sub-targets which outline specific milestones for 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.

The related sub-target states that 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
• all (100%) storm overflows discharging in or close to high priority sites by 2045
• all remaining storm overflows sites by 2050

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

In addition, it will also ensure 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.

The target protects biodiversity at both a local and national scale and will result in the complete elimination of ecological harm from storm overflows.

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.

This target is intended to 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 and 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. This target is expected 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.

Achieving the targets

The guidance states that 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.

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

The water companies must also 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 guidance sets out the principles the government expects the water companies to adhere to when achieving the targets, including compliance with all their existing regulatory obligations and duties e.g. permits issued by the Environment Agency.

It also emphasises that 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.

The water companies must ensure all their wastewater and drainage assets are working as intended, before implementing infrastructure upgrades, including proactive management and adequate maintenance of assets, with timely replacements, upgrades, or repairs of assets as appropriate.

It also sets out the penalties the water companies could face if they are found not to comply with their legal responsibilities, 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 ahead

The requirements on water companies to undertake comprehensive long-term planning with regards to the capacity and resilience of the sewage network forms part of the water companies’ Drainage and Wastewater Management Plan objectives. The water companies are expected to have maps of their sewer networks upstream of overflows,

According to the guidance, 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.

They will also be required to 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 - key expectations

The guidance slso sets a number of expectations are expect water companies to meet, including:

• achieve year on year reductions in the amount of surface water that is connected to their combined sewer network.
• remove rainwater from the combined sewer system - this includes limiting any new connections of surface water to the combined sewer network. Any new connections should be offset by disconnecting a greater volume of surface water elsewhere within the network.
• prioritise a natural capital approach, considering carbon reduction and biodiversity net gain, as well as catchment-level and nature-based solutions in their planning.

The guidance flags up green infrastructure and other nature-based solutions as an effective option to reduce the harm caused by storm overflows which can provide multiple co-benefits e.g. separating surface water so that it doesn’t mix with sewage and is diverted to water gardens or wetlands. This improves water quality, creates new habitats for species and acts as a carbon sink.

The Environment Agency and Ofwat will actively encourage companies to consider green infrastructure in their proposals to achieve the targets and operate in partnerships across catchments maximising co-funding and green finance opportunities, where appropriate, including through market mechanisms.

The guidance also acknowledges 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.

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, the guidance says.

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 rainwater by water companies

The guidance says the government 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:

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

Click here to access the supplementary guidance in full.