If you’re a homeowner with a septic tank or sewage treatment plant, you may have wondered whether rainwater can go into it. Perhaps you’ve considered the possibility of directing rainwater from your roof or outdoor paved services, into your system.
The short answer is; no – you can’t do this – and there are important legal, practical and environmental reasons why not.
UK building regulations requirements
As stated in Building Regulations Part H, surface water drainage systems must be kept separate from foul water drainage. This applies throughout England and Wales, to ensure that rainwater and sewage follow different paths.
Wastewater should be connected to a public or private sewer, septic tank or cesspool. But surface water should be disposed via a soakaway, a watercourse, a surface water or combined sewer.
What do the General Binding Rules say?
The Environment Agency’s General Binding Rules have been in force since 2020 but have been updated periodically. They provide further clarity on the prohibition of adding rainwater to sewage systems. And this isn’t just a recommendation – you’re legally required to operate your system along these lines unless you want to apply for additional permits.
How does rainwater damage my system?
If rainwater enters your septic tank, it can negatively affect the active bacteria present. These micro-organisms are responsible for decomposing the waste products that enter your tank. But large volumes of rainwater can ‘thin out’ wastewater, meaning it contains less organic material to digest.
And this diluted flow, carrying more indigestible substances such as sand from roofs and paving, can cause bacteria to become less effective. This can lead to problems including blockages, unpleasant odours, tank damage or wastewater flow into your garden.
And for sewage treatment plants specifically, large volumes of rain may even flush out the microbes completely.
How do I stop rainwater entering my system?
There should be no rainwater downpipes or surface drains connected to your sewage treatment system. And all roof and surface water should be directed to a separate soakaway or drainage system, positioned well away from your foul water setup.
Ensuring a sufficient distance between rainwater and sewage soakaways should prevent cross-contamination and system overload. But if you’re unsure whether or not your current system complies with these guidelines, you should ask a professional.
An expert inspection will help ensure that you meet all legal requirements and protect you against unwanted repair and maintenance bills.
Ready to rain-proof your system?
Keeping rainwater separate from your septic tank or sewage treatment plant isn’t just about following the rules. Ensuring your system works compliantly and efficiently for years to come will protect your investment and your peace-of-mind.
If you’d like to talk to an experienced professional about keeping rainwater out of your system, please contact us.