Guide
What you cannot discharge to a public sewer: section 111 explained
Updated
Recurring drainage problems on industrial sites are often a discharge problem wearing a blockage costume. Before you buy another jetting visit, it is worth knowing what the law says may not go into the sewer in the first place.
What section 111 actually prohibits
Section 111 of the Water Industry Act 1991 makes it an offence to throw, empty or turn into a public sewer, or into any drain or sewer communicating with one, several categories of thing (legislation.gov.uk). In summary, the section covers:
- any matter likely to injure the sewer or drain, to interfere with the free flow of its contents, or to affect prejudicially the treatment and disposal of its contents;
- chemical refuse or waste steam, or any liquid of a temperature higher than 43 degrees Celsius, in the circumstances the section describes as dangerous, a nuisance, or injurious to health;
- petroleum spirit or carbide of calcium, which the section names expressly.
The section sets out the penalties on summary conviction and on indictment, including the possibility of imprisonment and of daily penalties for a continuing offence. Read the section itself before relying on any summary of it, including this one.
What that means on a real site
- Fats, oils and grease are the everyday version of matter that interferes with free flow. A kitchen or food production line without working grease management does not have a blockage problem, it has a discharge problem that presents as blockages.
- Process effluent is a separate consent question. Trade effluent discharged to the sewer needs the sewerage undertaker's consent or an agreement, with its own conditions and charges. Ask your water company what your site holds before you assume anything is permitted.
- Fuel, solvent and oil-contaminated water belongs in an interceptor that is actually being serviced, not in the surface water system.
- Hot process water has a temperature limit written into the section. If your site discharges anything warm at volume, that is worth checking rather than assuming.
Turning a recurring blockage into a fix
- Survey before you jet again. A CCTV survey with a written report tells you whether the cause is a defect or a discharge. Repeated clearance visits with no diagnosis are a subscription, not a repair.
- Trace the source. Where a survey shows deposits rather than damage, the answer is upstream: a process, a wash-down, a kitchen, a failed separator.
- Fix the input, then the pipe. Cleaning a system that will be re-loaded next week buys a few weeks. Grease management, separator servicing or a process change is what stops the cycle.
- Record it. Keep the survey, the plan and the servicing records. They are what you produce when a water company, an insurer or an incoming tenant asks.
This page describes what the legislation says and is not legal or regulatory advice for your site. Trade effluent consents, discharge conditions and permits are matters for your water and sewerage company and, where relevant, the environmental regulator. Where you need work done, the contractors quoting through this site can survey the system and tell you what is coming from where.