Drainage and septic tanks
Does a home survey prove the drainage field meets the general binding rules?
No. The rules cover volume, the type of treatment, pollution, and distances from wells and protected groundwater, among other points. A surveyor walking the garden cannot certify those. They can say the system was not assessed against the rules.
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?
The official rules for small sewage discharges in England are a legal checklist. They include, for discharges to ground, a published limit of 2 cubic metres a day and restrictions near wells and source-protection zones. A home survey does not measure daily flow and does not map a groundwater zone. Treating a “tank seen” note as compliance is a mistake.
If compliance decides whether you buy, instruct someone who will assess the system against the rules and say what must change. Ask your solicitor to ask the seller what they know. Keep the survey’s drainage rating for the condition of what was visible: a broken cover, a flooded chamber, a smell. That rating is still useful. It is just not a permit.
What should you ask your surveyor?
- Please confirm you did not assess the general binding rules. That confirmation is worth having in writing if a seller claims you did.
- What visible defects should I still take seriously?
- What specialist should I ask, as distinct from another home survey?
What are the typical next steps?
- Do not tell a lender or a buyer of your own, later, that the survey signed off the tank.
- If you need certainty, pay for a proper drainage assessment and read the rules yourself.
- Separate “the cover is broken” from “the discharge is lawful”. Repair the first. Investigate the second.
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
Can the surveyor be sued for not checking the rules?
The terms of engagement set the inspection. A visual survey that says drainage was not tested has usually drawn that boundary. Read your terms. This page is not legal advice.
Does a building-control certificate for an old tank prove today’s rules are met?
It proves what was approved then, if the certificate is genuine. Rules have changed, including the October 2023 binding rules in England. Ask a competent person whether this system meets the current ones.