Drainage and septic tanks
A water-company map in the pack shows a public sewer in the road, not in the garden. Why does that map not describe the private run under the lawn?
That map does not describe the private run under the lawn, because it is a water-company plan of the public sewer and it shows that sewer in the road. A private drain in the garden is not the line the sheet was drawn to show. The survey does not turn the map into a plot of the private pipes, and putting the map in the pack does not make it one. A chamber or a gulley may have been seen. The private run under the lawn was not mapped by that sheet.
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?
Public sewer maps show the undertaker's sewers, here said to lie in the road. Private drains, the pipes from the house to the public sewer or to a tank, are often absent from that sheet even when they cross the lawn. The map is doing its job by showing the public line. Expecting it to trace the private run confuses two networks. The home survey does not redraw the company plan, and a company plan does not become a CCTV report because it was stapled in the pack.
The solicitor uses the water-company search for the public sewer and for any agreement the search actually reveals. The private run, if you need it, is a drain inspection on the ground. Tell them the map in the pack stops at the road. Do not assume the lawn has no drain because the coloured line is in the carriageway. Absence from a public map is not absence from the garden.
What should you ask your surveyor?
- What does the water-company map actually show, and where?
- Have you kept the private lawn run off that sheet?
- Did the survey plot private pipes, or only see what was open?
What are the typical next steps?
- Read the map as the public sewer in the road.
- Do not use it as a plan of the private drain under the lawn.
- Inspect the private run separately if you need it described.
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
If the map is a recent print, does it start to include private drains?
A recent print is still the product it says it is. This one shows a public sewer in the road. Recency does not add the private lawn run. The survey has not upgraded the sheet into a private-drain survey of the garden.
Can a public sewer in the road still take a private connection from the garden?
Yes. That is a common arrangement: a private pipe in the garden and a public sewer in the road. The map shows the public part. It does not draw the private connection. The survey has not traced that link either.