To ask the Secretary of State for Environment, Food and Rural Affairs, how many sewage treatment works are operated by each water company in England; and how many of these have temporary storm storage tanks with sufficient capacity to prevent overloading of the treatment works.

At some sewage treatment works, where the permitted treatment capacity may be exceeded due to rainfall, storm tanks form part of the treatment process to limit spills of storm sewage (mixture of sewage and rainfall) to the water environment. These discharges are permitted by the Environment Agency under the Environmental Permitting Regulations.

The number of sewage treatment works and permitted storm tanks at sewage treatment works for each water and sewerage company in England are set out in the table below:

1. Information from the Environment Agency Water Information Management System
2. Information from the Event Duration Monitoring – storm overflow – annual returns published by the Environment Agency Event Duration Monitoring - Storm Overflows - Annual Returns - data.gov.uk

The requirement for storm tanks is that they must settle out solids and have a minimum capacity of 68litres/head served or a storage equivalent of 2 hours at the maximum flow rate to the storm tanks.

In the current water company investment programme for the period 2020 to 2025 there are 534 sewage treatment works where there will be upgrades to storm tanks to meet the requirements. Information on these upgrades from the published Environment Agency Water Industry National Environment Programme is summarised in the table below: