Your options
- Septic tank with a drainage field. The tank settles the solids. The liquid drains away through perforated pipes laid in the ground, where the soil treats it. It needs free-draining soil and enough land.
- Sewage treatment plant. A powered unit that treats the waste water to a higher standard. It can discharge to a drainage field or, where the rules allow, to flowing water. It needs an electricity supply and regular servicing.
- Cesspool. A sealed tank with no discharge, emptied by tanker. It is normally the last resort, used where no discharge is possible, because of the cost of frequent emptying.
The rules a new system must meet in England
A new or replacement system must meet the general binding rules for small sewage discharges, or have an environmental permit. The main points are:
- The tank or plant must meet the British Standard that was in force when it was installed. For new equipment that is BS EN 12566.
- A drainage field must be designed and built to BS 6297:2007.
- A septic tank must not discharge directly to surface water.
- The installation needs Building Regulations approval, and a new discharge needs planning permission.
- A new discharge is not allowed if any part of the building is within 30 metres of a public sewer.
- You need a permit to discharge more than 2,000 litres a day to the ground or 5,000 litres a day to surface water, or to discharge to the ground in a groundwater source protection zone 1.
The government's guide to septic tanks and sewage treatment plants gives the full rules. Building Regulations guidance is in Approved Document H. The rules are different in Wales, Scotland and Northern Ireland, where a system is registered with or consented by the environmental regulator.
What an installer will need to know
- How many bedrooms the property has, or how many people the system will serve. This sets the size.
- Whether there is an existing tank, and what is wrong with it.
- Where the system can discharge: the size of the garden, the type of soil, and any ditch or stream nearby.
- Access for an excavator and a delivery lorry.
- Whether you already have a drainage survey. If not, see septic tank surveys.
A good installer visits the site and carries out a percolation test, which measures how fast water drains through the soil, before recommending a system. Ask each firm what their quote includes: the unit, excavation, the drainage field, electrical work, Building Control fees and making good.
How to get quotes
Use the form at the top of the page. Tell us whether it is a new system or a replacement, and your postcode. We pass your request to installers that cover your area. Installation is groundworks, not tanker work, and most emptying firms do not offer it, so we match the request to the work. Get more than one quote, and compare what each includes.