Blocked Drain vs Blocked Sewer: How to Tell the Difference

Why the Distinction Matters

When water backs up in your sink, toilet, or outside gully, the instinct is to call a plumber immediately. That's usually the right call — but understanding whether you have a blocked drain or a blocked sewer affects who fixes it, how quickly, and importantly, who pays. In some cases, the problem isn't yours to resolve at all.

The Difference Between a Drain and a Sewer

A drain carries wastewater from a single property. Everything from your kitchen sink, bath, toilets, and washing machine runs through your private drains until it reaches the public sewer. Your private drains are entirely your responsibility — from the fittings inside the house to the point where they connect to the main sewer, typically under the pavement or road outside.

A sewer is a shared pipe that collects wastewater from multiple properties and carries it to the treatment works. Since the Water Industry Act 2011, most sewers in England are the responsibility of the regional water and sewerage company — in Peterborough, that's Anglian Water. You are not responsible for a blocked shared sewer, and you should not pay to have it cleared.

The boundary between your drain and the public sewer is the point where your private pipe connects to the shared one — usually around the edge of your property or just beyond it.

Signs It's Your Private Drain

The clearest sign of a private drain blockage is that the problem is confined to your property. If water backs up in your kitchen but your neighbour's drains are fine, the blockage is in your private drainage. Other signs include:

• A single fixture slow to drain — just the bath, or just the kitchen sink, while others work normally
• Gurgling from a waste pipe or drain that corresponds to use of one specific appliance
• A smell from one drain in particular rather than throughout the property
• Water backing up through a ground-floor drain when you run water upstairs

Most private drain blockages are caused by accumulated grease and food waste in kitchen pipes, hair and soap residue in bathroom wastes, or physical objects flushed down toilets. Our guide to unblocking a drain covers what you can try yourself and when to call a plumber.

Signs It's the Shared Sewer

If the problem is affecting multiple properties simultaneously, the shared sewer is the likely cause. Indicators include:

• Your neighbours have the same drainage problem at the same time
• The outside inspection chamber (manhole) is overflowing or backed up
• All drains in your property are slow or blocked at the same time, with no obvious single source
• Raw sewage appearing in your garden or outside drain — particularly if it affects adjacent properties

If you suspect a shared sewer blockage, report it to Anglian Water directly on 03457 145 145. They are legally obligated to investigate and clear blockages in the public sewer network at no charge to you.

The Complication: Shared Private Drains

There's a third scenario that causes confusion — a private shared drain. This is a drain serving more than one property but which was not adopted by the water company under the 2011 Act. These remain the joint responsibility of the properties they serve, meaning you and your neighbours share the cost of clearing and maintaining them.

If you're unsure whether a drain is shared or adopted, Anglian Water can provide drainage maps showing the extent of the public sewer network. Your conveyancing solicitor should also have noted any shared drainage arrangements when you bought the property.

Inspection Chambers: A Quick Check

The fastest way to get information is to lift the nearest external inspection chamber (manhole) on your property. If it's full of standing water or sewage, the blockage is likely downstream of that point — either in a shared sewer section or further along your private drain. If it's empty and clear, the blockage is between the chamber and the house, squarely on your private pipework.

Not sure where your inspection chambers are? Our drainage team can locate, lift, and assess external chambers as part of any call-out. If the blockage appears to involve the shared network, we'll document the findings so you can report to Anglian Water with evidence. Book online or call 02039514510.

Frequently Asked Questions

Who is responsible for a drain under my driveway?

If the drain only serves your property, it's your responsibility regardless of where it runs — including under your driveway, garden, or even under the pavement to the sewer connection point. The public sewer begins where your drain meets the shared network, which is often slightly beyond your property boundary.

My neighbour and I share a drain — who pays to clear it?

If the drain was not adopted by Anglian Water under the 2011 Act, it remains a private shared drain and both parties share maintenance responsibility. Costs are typically split equally. It's worth checking with Anglian Water whether the drain qualifies for adoption — many post-2011 adoptions are still being processed and yours may now be a public sewer.

Can Anglian Water refuse to clear a blocked sewer?

No — if a blockage is confirmed to be in the public sewer network, Anglian Water is legally obligated to clear it under the Water Industry Act 1991. If they fail to respond within a reasonable time and sewage is escaping onto your property, you can escalate to the Consumer Council for Water (CCW).

Can I use drain unblocker chemicals on a shared drain?

Chemical drain cleaners are generally ineffective on anything beyond minor household waste blockages, and can damage older clay drain pipes. For any blockage beyond a single sink waste, mechanical or jetting clearance from a qualified drainage engineer is more effective and far less likely to cause collateral pipe damage.

Private Drains vs Public Sewers: Who Is Responsible?

Understanding this distinction matters because it determines who is responsible for clearing the blockage and who bears the cost. In England, the boundary between private drains and the public sewer network was extended in 2011 when Ofwat transferred responsibility for shared private sewers to water companies. Most lateral drains — the pipes running from your property to the public sewer — are now Anglian Water's responsibility in the Peterborough area.

Signs the Problem Is in Your Private Drain

If only your property is affected — one or more drains are slow or backed up but your neighbours' drainage is working normally — the blockage is almost certainly in your private drain, which runs from your property's external wall to the public sewer connection. You are responsible for clearing this section.

Signs the Problem Is in the Public Sewer

If multiple properties in your street are simultaneously experiencing drainage problems, the blockage is likely in the public sewer. Contact Anglian Water's emergency number — 03457 145 145 — to report the issue. They will attend, investigate, and clear blockages in their network at no cost to you. Do not engage a private contractor to clear a public sewer blockage — you will be charged for work that Anglian Water is obliged to carry out for free.

What to Do If the Public Sewer Is Blocked

If your investigation of inspection chambers confirms the blockage is beyond your property boundary — in the lateral drain or the public sewer — contact Anglian Water immediately. Their contact number for drainage emergencies is 03457 145 145 (24 hours). Report the blockage with your full address and a description of the symptoms (inspection chamber overflowing, sewage backing up, number of properties apparently affected). Anglian Water has a statutory duty to maintain the public sewer network and will attend, typically within 4 hours for a confirmed sewer flooding situation. Do not attempt to clear a public sewer blockage yourself — the network is under their ownership and liability.

Private Drain Repairs vs Sewer Adoptions

The 2011 transfer of lateral drains to sewerage undertaker ownership was not retrospective for all drains — there are edge cases, particularly for private sewers shared between properties but not yet formally adopted, where ownership boundaries remain unclear. If Anglian Water attends and determines that the affected drain is not on their asset register (not yet adopted), they will leave without clearing the blockage. In these cases, you will need to commission a drainage engineer yourself and may need to liaise with adjacent property owners if the drain is shared. A CCTV drainage survey mapping the drain route and confirming its connection to the public sewer provides the evidence needed to challenge a refusal of adoption. Call 01733 797074 for drainage surveys and blockage clearance across all PE postcodes.