Top 5 Drainage Checks Every Buyer Should Make Before Buying a London Home

One of the biggest misconceptions among homebuyers is that a standard homebuyer or RICS survey includes a detailed inspection of the property's drainage system. In reality, underground drains are rarely examined beyond visible signs of concern, meaning serious defects can remain hidden until after completion.

This is particularly important in London, where Victorian and Edwardian homes make up a significant proportion of the housing stock. Many of these properties still rely on ageing drainage infrastructure that may be vulnerable to cracking, root intrusion or historic repairs. Across England, around 37% of homes were built before 1945, highlighting the prevalence of older housing and infrastructure.

Whether you're buying your first flat, moving to a family home or investing in a buy-to-let property, carrying out a few simple drainage checks before exchange can help you avoid costly surprises later.

Quick Buyer Checklist

Before exchanging contracts, make sure you have:

✓ Considered a CCTV drainage inspection

✓ Confirmed who is responsible for the drains

✓ Reviewed drainage and flood-risk information

✓ Checked for mature trees near drain runs

✓ Understood how the property's drainage system is connected

What a CCTV drain survey shows

Many drainage problems are impossible to identify during a viewing. A property can appear perfectly maintained while hidden defects exist beneath the ground.

This is why many buyers choose to arrange a professional CCTV drain survey before committing to a purchase. Using specialist camera equipment, the survey can reveal cracks, displaced joints, root ingress, collapses, blockages and bellied (sagging) pipework that would otherwise remain unseen.

A pre-purchase drain survey can also identify signs of previous repairs, recurring issues and ageing infrastructure that may affect future maintenance requirements.

When to book it during conveyancing

The best time to arrange a drain inspection before buying a house is after your offer has been accepted but before contracts are exchanged.

If defects are discovered at this stage, buyers can seek further information, obtain specialist advice or use the findings to support negotiations. Once the exchange has taken place, any hidden drainage issues generally become the buyer's responsibility.

For many purchasers, a homebuyer's drain survey provides reassurance that one of the property's most important systems has been properly assessed before completion.

Public vs private drains since the 2011 sewer transfer

Responsibility for drainage infrastructure is not always straightforward.

In October 2011, ownership of most private sewers and lateral drains connected to the public network transferred to water and sewerage companies, according to the guidance published by Ofwat. The change was introduced to simplify maintenance responsibilities and reduce disputes over shared infrastructure.

However, responsibility can still vary depending on the pipework's location and purpose, so it is always worth confirming the position during conveyancing.

Shared drains in terraced streets

This is particularly important in London's terraced streets, where multiple properties often share sections of drainage infrastructure.

While some shared sewers may fall under the responsibility of the local water company, drains serving only the individual property and located within the boundary commonly remain the homeowner's responsibility.

Useful questions to ask include:

• Who is responsible for shared drains serving the property?

• Have any drainage repairs been carried out recently?

• Are there known drainage disputes or access arrangements?

Watermarks, tide lines and the “musty” basement test

Even without specialist equipment, buyers can often spot warning signs during viewings.

Common signs of drainage problems in older homes include damp patches, watermarks, musty smells, slow-draining sinks, gurgling pipework and unpleasant odours around kitchens or bathrooms.

Outside, look for standing water, uneven paving, recently disturbed ground or inspection chambers that appear to have been repaired or replaced.

While none of these signs automatically indicate a serious defect, they may justify further investigation.

Checking the flood-risk and drainage searches (CON29DW)

Property searches can reveal issues that are not immediately visible.

The CON29DW drainage and water search provides information about connections to public sewers and water mains, while flood-risk checks can help identify potential exposure to river, coastal or surface-water flooding.³

It is also worth asking the seller or estate agent whether the property has experienced flooding, drainage-related insurance claims or recurring drainage issues in the past.

Which trees cause the most drainage damage

Trees are often a desirable feature, but mature root systems can sometimes create drainage problems.

Species such as willow, poplar and mature sycamore trees are known for seeking moisture underground. Where older pipe joints have weakened over time, roots can exploit small openings and gradually enter the drainage system.

This risk is particularly relevant in older London properties that still have clay pipework beneath the ground.

How root intrusion shows up on a survey

Tree roots in drains do not always produce obvious symptoms at first. In many cases, they cause minor restrictions before developing into recurring blockages or structural damage.

Drainage specialists inspecting Victorian and Edwardian properties across London frequently encounter root intrusion in ageing clay pipes. A CCTV survey can confirm the extent of the problem and whether remedial work may be required.

Combined vs separate systems in older London areas

Not all drainage systems operate in the same way.

Many older London homes were built with combined drainage systems, where rainwater and wastewater enter the same sewer network. Newer properties are more likely to use separate systems.

Understanding how the property is connected can help buyers better understand how the system may perform during periods of heavy rainfall.

Surface water, soakaways and where the rain actually goes

It is also worth understanding where rainwater from roofs, patios and driveways ultimately drains.

Depending on the property, surface water may discharge into a public sewer, a soakaway or another approved drainage arrangement.

Ask whether extensions, landscaping works or driveway installations have altered drainage routes, and whether any drainage plans are available as part of the conveyancing process.

A drainage concern does not necessarily mean you should walk away from a property.

Instead, treat it as valuable information that helps you make a more informed decision. Some issues may require little more than routine maintenance, while others could justify further investigation before contracts are exchanged.

Speak with your conveyancer, request clarification from the seller and seek specialist advice where appropriate. The aim is not to eliminate every risk but to understand the property's condition before committing.

Because drainage systems are largely hidden from view, a small amount of due diligence before exchange can help prevent inheriting disruptive and potentially expensive problems later on.