England Storm Overflow Discharge Duration and Frequency Annual Reports

Annual regulatory returns detail the frequency and duration of discharges from monitored storm overflows in England. Data spans from 2020 to 2025, with key summary tables and long-term trends from 2016. The Environment Agency compiles this information from submissions by 10 Water and Sewerage Companies.

Use Cases

• Analyze trends in average spill duration and average spill count per water company from annual summary tables.
• Identify storm overflows with high spill counts and investigate provided reasons for high discharges from 2021 onward.
• Compare long-term performance trends from 2016 to 2025 using the consolidated trend data file.
• Assess the operational status of event duration monitors by reviewing reasons for monitors providing data for less than 90% of the reporting period.

Strengths

• Covers 6 consecutive years of annual data (2020-2025) for longitudinal analysis.
• Includes data from 10 distinct Water and Sewerage Companies operating in England.
• Provides explanatory metadata for data gaps (monitor uptime <90%) and high spill events from 2021.

Limitations

• Specific row counts and column details for the raw overflow-level data are not provided.
• Data is limited to England, excluding other UK nations.
• Relies on self-reported data from water companies, subject to their internal data collection quality.

Provenance

Source

Environment Agency, UK.

Collection Method

Mandatory annual returns submitted by Water and Sewerage Companies (WaSCs) under the Environmental Permitting Regulations.

Time Range

Primary detailed data from 2020 to 2025, with summary trend data from 2016 to 2025.

Freshness

Updated annually; most recent data is for 2025, with files updated in March 2026.

Geography

England.