When building a home from scratch, there?s plenty that needs planning before you start – including drainage and sewerage. You need to work out where water comes in and waste goes out, and whether you’ll connect to the mains service, or come up with an off-mains solution.

There are two types of drainage: foul water and surface water. Foul water covers sinks, showers, baths and WCs; surface water is rainfall that drains off your property. If you can find a way to prevent rainwater from draining off your property and into the public sewers, consider using it: you may be entitled to a surface water drainage rebate, i.e. a discount on your water bill, even if your foul water empties into the public sewer system as normal

In any case, you’ll need plastic or clay drains, with plastic or brick inspection chambers at every point where there;’s a bend in the drain. What happens next depends on where the water’s going.


Connecting your drains to publicly owned mains sewers poses a logistical problem, since you can only build up to the edge of your property. To complete the connection, you need an approved contractor to extend your drain onto public property (the road and drainage system outside). We’re on the approved contractor list for Welsh Water and Severn Trent Water, and glad to provide quotes for connecting self-build properties to the mains in Wales and the West of England.

Deciding on drainage:
If you want a mains connection, you’ll have to hire an approved contractor.

The other problem you may face is a practical one. If your property is built at a lower level than the public drain, you may need a domestic pump – an installation which collects foul water and then pumps it upwards into the mains drain.


If your self-built home is too far from the sewers for mains drainage to be an option, you need an on-site solution. For surface water, you’ll need a soakaway: a series of covered trenches from which water can drain back into the ground.

For foul water, you’ll need a small treatment plant, a septic tank or a cess pit. Treatment plants treat the foul water to remove the worst of the contaminants, and a septic tank sifts the solid waste from the liquid, allowing the liquid to disperse into the ground. However, this depends on a few environmental factors – how porous your property’s soil is, and how close your tank is to natural watercourses or other prohibited areas. If a septic tank won’t work, or isn’t permitted, you’re looking at building a cess pit – a deep, sealed underground tank which contains all your foul waste, liquid or otherwise.

There’s a lot to consider when planning and building the drainage for a self build. There are legal restrictions and implications to all your choices, as well as extensive costs for more elaborate systems.

The good news is, we can talk you through the options before you, help you choose and plan, and carry out the work of installation and maintenance too. Tell us about your property and we?ll see how we can help.