Dry spilling
A spill in dry weather has no rainfall to excuse it. The same overflows do it year after year.
A storm overflow may discharge only in exceptional circumstances. Regular spilling in normal or moderate rainfall is a prima facie breach of regulation 4 of the Urban Waste Water Treatment Regulations 1994.
This reading follows the Office for Environmental Protection's December 2024 findings against Defra, the Environment Agency and Ofwat, which set out a two-stage test â was the discharge caused by exceptional circumstances, and was it nonetheless kept to a minimum â and Defra's 24 March 2025 guidance, which supersedes the 1997 guidance the regulators had relied on.
Repeat dry-weather offenders
Each overflow's per-spill confidence (gauge proximity, antecedent-dry window, monitor uptime) is shown on every event's evidence dossier.
How we decide a spill was dry
A spill is counted as dry when rainfall at the nearest gauge was ⤠0.25 mm on the spill day and the day before, and the spill lasted at least 15 minutes. Confidence rises with a closer gauge, a longer antecedent-dry window, and a monitor that was reporting reliably. Read the full method â
Why this now carries more weight
A dry-day spill is a pollution incident regardless of its volume. Dry-spill frequency is a scored metric in the Environment Agency's 2026â30 regime, and updated incident guidance removes companies' former latitude to downgrade these events. A pattern of them is exactly what a regulator is now expected to act on.
Dry-spill method â · figures reproducible against the pinned method version.