Drainage and septic tanks
What daily volume do the English general binding rules set for a small discharge to ground?
For a discharge to ground, the rules in force from 2 October 2023 say the discharge must be 2 cubic metres or less a day, and the sewage must be treated by a septic tank and infiltration system or by a treatment plant and infiltration system. A home survey does not measure that volume and cannot tell you the household meets the rule.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
“To ground” means an infiltration system, often called a drainage field, not a pipe to a ditch. The volume limit is on the GOV.UK general binding rules page. It is not a figure the surveyor calculates from the number of bedrooms, unless they have done that design, which a visual survey does not do. Exceeding the limit, or discharging without the infiltration system the rule describes, can take the system out of the binding rules and into a permit.
Ask the seller where the outlet goes and for any permit or registration papers. Your solicitor, not the surveyor, checks that against the drainage search. If the cover was not lifted and the field was not found, the survey has not proved compliance. Wales, Scotland and Northern Ireland have different rules. Do not carry the English 2 cubic metre line across the border.
What should you ask your surveyor?
- Did you see an infiltration system, or only a tank?
- Are you making any statement about daily volume?
- What papers should the solicitor ask for if the seller says the tank “meets the rules”?
What are the typical next steps?
- Do not calculate a volume yourself from a bedroom count and call it the law.
- Ask the seller where the effluent goes, in writing.
- If compliance matters before exchange, instruct someone who will trace the outlet, and tell your solicitor what they find.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is 2 cubic metres the same as the surface-water limit?
No. The surface-water rules on the same page use 5 cubic metres a day and require a treatment plant. Do not swap the numbers.
Does a new family in the house change the volume?
Use changes volume. The survey cannot predict your household. If you are close to a limit, ask an installer, not the condition rating.