Sewage Backing Up Into The Bath Or Shower

What's happening?

Water finds the lowest opening. When a drain run is fully blocked and something upstream keeps discharging into it, the sewage rises until it reaches the first fitting below the blockage that it can escape from — which in most UK houses is a ground-floor shower tray or a bath, because those sit lowest. That is why sewage in a downstairs shower is not a shower problem at all; it is a fully blocked drain announcing itself in the worst possible way. It also means the blockage is downstream of the whole house, so every additional flush, wash cycle and tap makes the flooding worse. Stop using water first, work out where the blockage is second.

What usually causes it?

• A complete blockage in the private drain between the house and the boundary
• A blockage in the shared lateral drain or the public sewer, so the whole property backs up
• A collapsed section of drain that has finally closed the bore entirely
• A mass of fat, wipes and sanitary items at a bend or a junction
• Tree roots that have filled the pipe and then trapped debris behind them
• Surcharging of the public sewer during heavy rain, pushing water back up private drains
• A missing or defective non-return valve on a property known to be at risk of backflow

When should you call a drainage engineer?

Ring your sewerage company immediately — internal sewer flooding is something they respond to as an emergency, and if it originates in the public sewer or a transferred lateral it is theirs to clear at no charge. Call a drainage engineer in parallel, or if the water company confirms the blockage is inside your boundary. Once the drain is clear, treat the cleaning and drying as a separate job and tell your insurer before anything is stripped out.

What will the drainage engineer actually do?

• Locate the blockage by reading the chambers from the house to the boundary
• Clear it by jetting or machine and relieve the backed-up sewage under control
• CCTV survey the run to find the collapse, root mass or defect that caused a total blockage
• Confirm which lengths are private drain and which are the sewerage company's responsibility
• Advise on a non-return valve or anti-flood device where the property is at risk of surcharge
• Provide a survey report suitable for an insurance claim and for planning any repair

Stop the flow first

1. Stop every flush, tap, shower and appliance in the property.
2. Close the door on the affected room and keep children and pets out.
3. Lift outside chamber covers to see how far the backup reaches.
4. Ring your sewerage company and report internal sewer flooding.
5. Photograph the affected rooms before anything is cleaned or moved.
6. Tell your insurer before agreeing to any strip-out or drying work.