Devon and Cornwall septic tanks linked to 91 pollution incidents

If your home is not on mains drainage, the tank at the bottom of the garden is your responsibility. And new figures suggest that across Devon, Cornwall and the Isles of Scilly, things went wrong 91 times in a decade.

The numbers come from a Freedom of Information request to the Environment Agency (EA), submitted by septic tank and waste management specialist CSG. It asked how many pollution incidents involving septic tanks or private sewage systems were recorded between 2015 and 2025.

What the figures show for Devon and Cornwall

According to the EA, there were 91 incidents in Devon, Cornwall and the Isles of Scilly over that period. Of those, 17 were recorded in 2025.

Across England the total was 1,184, with 69% of cases at domestic properties.

Nationally, 120 incidents were recorded in 2025, up from 78 in 2024 and 89 in 2023. The highest year in the figures was 2021, with 152.

The full statistics from the FOI request are on the CSG website.

Who relies on septic tanks

CSG says an estimated three million UK households use cesspits or septic tanks instead of the main sewage system, usually through necessity.

The company cleans more than 20,000 septic tanks each year. Group Operations Manager David Cashmore said: “There are millions of people across the country who rely on private sewage systems. The vast majority are maintained effectively but we wanted to find out the extent of the pollution problem.

“Faulty septic tanks can cause serious issues, including polluted streams and waterways, contamination of watercourses, bad smells and harm to fish and wildlife.”

What owners are expected to do

EA rules state that septic tank owners must arrange emptying once a year, or in line with the manufacturer’s instructions.

David added: “Under Environment Agency rules, non-compliant septic tanks can lead to enforcement notices and fines so it is important owners take the issue seriously and deploy a robust maintenance strategy.”

Fewer officers, one prosecution

The same request asked about enforcement. According to the information obtained from the EA, the number of Land and Water Environment Officers responsible for septic tank enforcement and compliance fell from 303.5 full-time equivalent posts in 2014/15 to 182.5 in 2024/25.

And between 2015 and 2025 there was one prosecution for “illegal discharging by septic tanks or private sewage systems”. It was in 2019, in the Cumbria and Lancashire region.