Quick answer
Thames Water clears blockages in the public sewers that it owns. However, it does not look after the drain that serves only your home inside your boundary. If only your home is affected, the blockage is probably in your own pipe. If the problem is outside your boundary, or in a pipe shared with neighbours, report it to Thames Water.
What Thames Water says it owns
Thames Water says it owns and repairs the public sewers under roads and footpaths. It also says it looks after sewers that you share with neighbours. That stays true even though the pipe may run under your garden or driveway.
The reason goes back to 2011, since shared drains and the parts of a drain outside the boundary moved to the water companies that year. The guide to the 2011 private sewer transfer explains what moved and what did not.
What stays with the householder
Thames Water says you are responsible for waste pipes inside your boundary, as long as they serve only your property. That covers gullies, gutters and drains. For a blockage in that part, its page tells you to contact a drain clearing company.
Government guidance from 2011 says the same thing. Specifically, a drain that serves one property and sits inside its boundary stays with the owner or occupier. If your own pipe is the problem, blocked drain help in Aldershot is one way to start a request.
How to tell which pipe is blocked
Thames Water gives two simple clues on its blockages page. For example, a blockage may be yours if only one home has a problem. It may be the company's if the problem lies outside your property boundary.
Citizens Advice adds some practical steps. You can ask the sewerage company, check your deeds, request a sewer map or ask the local council. A CCTV drain survey can also help, because it shows the condition of a pipe and where a fault sits. The post on who is responsible for a blocked drain goes through the three pipe types in more detail.
Why you should not dig up or jet a public sewer yourself
Government guidance is clear on one point. A householder may only commission work inside the private drain, and you need to contact the sewerage company first before any work in a public sewer or public lateral drain.
The same guidance warns that interfering with a public sewer without consent may lead to prosecution. As a result, it pays to find out who owns the pipe before anyone starts work. If you think the pipe may be public, report it first.
What usually causes the blockage
Thames Water lists the usual causes on its blockages page. Fat, oil and food scraps that set hard in pipes come first. Wet wipes come next, and the company says that even wipes labelled flushable still block pipes. Sanitary items are the third cause it names.
Those causes can block your own drain just as easily as a public sewer. For example, a blocked toilet that keeps returning often points to something flushed that should have gone in the bin. The blocked toilet page explains what to send in a request for that problem.
Which company covers your town
Council documents from 2014 to 2018 name Thames Water as the sewerage company for most of the towns on this site. That includes Rushmoor, which covers Aldershot and Farnborough. It also includes Guildford Borough.
Those documents are several years old, so check which company serves your road before you rely on them. If you are in Farnborough, the drain unblocking page for Farnborough explains what to send in a request.
What to say when you report a problem
Good details help whoever picks up your report, because they show where to look first. Say where the water is coming from and which fixtures are affected. Say whether neighbours have the same problem. Say whether sewage is coming up inside the home.
Sewage inside the home is the most urgent case. The emergency drain services page explains what to send in that situation. If you are in Guildford, the emergency drain page for Guildford covers the same ground for your area. You can also read the emergency drain problems guide while you wait.
What if Thames Water says the pipe is yours
Sometimes a report ends with the answer that the blockage sits in your own pipe. In that case, Thames Water advises you to contact a plumber or a drain clearing company when the blockage is inside your drains. At that point the work becomes a private job between you and the engineer.
The Thames Water pages used for this post do not say whether a charge applies to public sewer work. Therefore, ask when you report the problem. Keep a note of what you were told, and the date. A clear record helps if you later need to explain who said what.
When to send a request
If the blockage looks like it sits in your own drain, you can send a request through the contact page. While you wait, keep notes of what you see. You send your details through the form. The site passes the request on so an engineer can respond.
The engineer who takes your job runs a separate business. As a result, the engineer sets the price, the arrival time and what cover applies afterwards. Ask for a written quote and agree all three before work starts. If you think the blockage is in a public sewer, report it to Thames Water instead.