What happens to water after it leaves my sink? Who owns which pipe?

Wastewater from your sinks, baths, showers, toilets and appliances flows through internal waste pipes into underground drains. These connect to a larger sewer, usually under the road.

Two terms matter for responsibility:

A drain carries wastewater from a single property. You own it and are responsible for it, including the section that runs under your garden.
A lateral drain is the part that runs outside your boundary before joining the public sewer. Since 2011, most lateral drains and shared private sewers in England and Wales are the responsibility of the water company, not the homeowner.

Knowing where your responsibility ends matters when a blockage strikes, because it affects who pays. If a blockage sits within your property boundary, it is yours to resolve. If it is in the public sewer, your water company handles it.

Most homes have one or more inspection chambers (manholes) where pipes meet or change direction. Lifting the cover lets an engineer see whether water is flowing or backed up, which quickly narrows down where a blockage sits.