What is a House purchase survey

A house purchase drainage survey is a specialist inspection that assesses the condition and layout of the drainage system in and around a property before its sale or purchase. Unlike general property surveys (such as the RICS HomeBuyer Report), a drainage survey is not typically included in standard homebuying packages, yet it plays a crucial role in identifying hidden defects, misconnected pipework, blockages, root ingress, or structural damage to underground drains.

The survey provides prospective buyers and their solicitors with critical information about the functionality, legal compliance, and future maintenance liabilities associated with the property’s foul and surface water drainage systems.

Why Drainage Surveys Are Important During Property Purchase

While structural and valuation surveys offer a broad assessment of a building’s condition, they often overlook below-ground infrastructure, which may be inaccessible without specialist equipment. A defective or non-compliant drainage system can lead to:

  • Costly repairs or replacements after purchase
  • Insurance complications if issues arise later
  • Disputes over property boundaries or shared drains
  • Environmental damage or pollution fines from illegal discharges
  • Flooding or foul odour issues

By commissioning a dedicated drainage survey during the conveyancing process, buyers gain peace of mind and legal clarity.

What the Survey Covers

A comprehensive house purchase drainage survey typically includes:

1. CCTV Drain Inspection

  • A camera is inserted into the drain system to record visual footage of pipe interiors
  • Identifies blockages, cracks, collapses, root ingress, displaced joints, and debris

2. Drainage Mapping

  • Produces a schematic of the property’s drainage layout
  • Shows connections to foul and surface water systems
  • Confirms whether drainage connects to mains sewer, septic tank, or soakaway

3. Condition Reporting

  • Highlights any structural defects or obstructions
  • Assesses flow conditions and pipe gradients
  • Checks for backfalls or poor installation practices

4. Misconnection Checks

  • Verifies that toilets, sinks, and appliances discharge to the foul system
  • Ensures surface water is not routed to foul drains or vice versa (a common pollution issue)

5. Ownership and Responsibility

  • Identifies shared drains or lateral sewers
  • Assists in clarifying what sections fall under the homeowner’s responsibility versus the water authority

Survey results are typically presented in a written report with images, diagrams, and professional recommendations for repair or maintenance where required.

When Is a Drainage Survey Recommended?

A drainage survey is especially important in the following scenarios:

  • Older properties with potentially outdated or unknown drainage infrastructure
  • Properties with a history of subsidence or flooding
  • Homes with extensions or renovations that may have altered drainage layouts
  • Rural properties using septic tanks or private systems
  • Properties near trees, where root intrusion may be a risk
  • Pre-auction purchases, where buyers have limited legal recourse

Some mortgage lenders or insurance companies may also request a drainage survey if concerns arise during the general property inspection.

How the Survey Is Carried Out

Most house purchase drainage surveys are completed in a single visit by a qualified drainage contractor. The process involves:

  1. Accessing manholes or inspection chambers
  2. Feeding a camera into the drainage system
  3. Recording footage and mapping the system using sonar or tracing dye if needed
  4. Analysing the data to produce a condition and connectivity report

No digging is usually required, and disruption to the property is minimal.

Compliance and Professional Standards

Drainage surveys should be conducted by professionals trained in CCTV inspection and reporting, often certified under:

  • NADC (National Association of Drainage Contractors)
  • WRC-compliant software and survey grading (e.g. to MSCC5 standards)
  • WRc Approved™ contractors where required for regulated works

For legal and technical accuracy, reports must be clear, well-documented, and suitable for presentation during the conveyancing process.

Benefits to Buyers and Sellers

For Buyers:

  • Gain assurance about underground infrastructure
  • Identify hidden issues before purchase
  • Strengthen negotiating position if repairs are needed

For Sellers:

  • Avoid post-sale disputes or claims
  • Speed up conveyancing by addressing drainage questions proactively

In some cases, sellers may commission a drainage survey in advance and include it in the property pack.

Conclusion

A house purchase drainage survey is a valuable due diligence tool that helps uncover defects in a property’s underground drainage network before contracts are exchanged. As these issues often lie outside the scope of standard building surveys, prospective buyers are strongly advised to commission a specialist inspection — particularly for older properties, those with complex drainage histories, or in flood-prone areas. With clear insights into drain condition, layout, and legal responsibility, a drainage survey supports informed decision-making and long-term confidence in property investment.