Drain misconnections: ask where each appliance discharges

Thames Water describes a misconnection as household wastewater plumbing connected incorrectly to a surface water drain. That can take untreated wastewater into rivers and streams. The problem is the destination, so apparently normal drainage does not settle whether the connection is correct.

Do not assume that every home has separate foul and surface water systems. Northern Ireland's nidirect guidance also explains combined drainage. Ask a competent professional to establish the arrangement before concluding that a particular pipe is wrong. The same drawing should not be applied to every property.

Sources: Thames Water; nidirect.

List the appliance or room concerned, any recent plumbing alterations and the reason for the concern. Include any letter from the water company and offer existing drainage plans. Describe what you have noticed without claiming a cause you have not established.

Our suggested appliance list has a row for each item, its location, any known alteration and a blank space for the investigator's confirmed destination. Leave unknown outlets blank. You do not need to open chambers, disconnect appliances or run a home dye experiment to prepare the list.

• Kitchen and utility-room appliances.
• Bathroom and toilet connections relevant to the concern.
• Altered rooms or recently added plumbing.
• Any supplied reference, plan or previous investigation.

Sources: nidirect; Thames Water.

Thames Water describes dye tracing as one method its team may use to follow wastewater. Ask the professional whether tracing, CCTV, a plumbing inspection or a combination is needed for your question. Agree the method and safe access arrangements with them, rather than buying a camera package by name alone.

Request a clear distinction between a route observed during testing, a route inferred from a plan and a connection that could not be checked. Ask how the receiving system has been identified. A record that water appeared at a chamber is only useful if the report explains which chamber and what that observation establishes.

Sources: Thames Water.

Use the appliance list to check the returned findings. For each tested item, ask for the identified route, method, result and any uncertainty. Request a marked sketch or labelled photographs where they help explain the conclusion. These are proposed reporting questions, not a promise that every investigation supplies those formats.

If correction is recommended, ask which recorded connection is to be changed and who must agree the work. Obtain a separate written proposal. Ask how the contractor will demonstrate the corrected destination afterwards and who needs the result, particularly if the water company initiated the investigation.

Sources: Thames Water; nidirect.

Thames Water's guidance concerns its service area. The nidirect advice is for Northern Ireland and directs tenants to their landlord about correcting wrong connections. Elsewhere, check with the relevant sewerage provider, landlord or local authority as appropriate. This page does not determine legal liability or permission to alter a public sewer.

Do not enter chambers or pour chemicals into a drain to try to establish a route. HSE identifies serious confined-space risks. If you suspect active pollution, use the relevant provider or environmental regulator's reporting route rather than waiting for a routine survey appointment. This website cannot receive or dispatch an emergency report.

Sources: Thames Water; nidirect; HSE.

• Are we checking a separate or combined drainage system?
• Which appliances and outlets will be traced?
• What method will establish the destination?
• Which connections remain untested or uncertain?
• Will the report link each finding to an appliance and outlet?
• Who needs to agree any correction?
• How will the corrected connection be checked afterwards?

Find and check a drainage contractor when you are ready to ask for quotes.