Which system suits your property? Matching a cesspool, septic tank or treatment plant to your ground, your space, the nearest water, power, access and use.
At KP Cesspool Services, we regularly speak to homeowners who are unsure which private drainage system suits their property. The honest answer is that the site usually decides, not the owner's preference. The ground, the space, whether there is a stream nearby, how far the tanker has to reach and how the house is used will rule some options out before cost even comes into it. This guide works through those features one at a time, so you can see which system your property points towards. If you want the systems themselves compared side by side first, cesspools vs septic tanks and the difference between a treatment plant and a septic tank cover that.
Start with the sewer
If a public sewer runs within reach, connecting to it nearly always beats all three. The General Binding Rules cannot be used at all if a public foul sewer is within 30 metres of the property's boundary, and the Environment Agency will not permit a private discharge where a connection is reasonable. Only if there is no sewer to reach does the choice below arise.
Your ground
The ground decides more than anything else, because two of the three systems put water back into it.
A septic tank needs a drainage field, and a drainage field needs soil that drains at a moderate rate. The ground has to pass a percolation test within a set range, there must be at least 1.2 metres of unsaturated soil above the water table at the wettest time of year, and the field has to sit at least 10 metres from any watercourse and 15 metres from any building.
On the chalk of the North Downs and on lighter, sandier soils, those tests are often passed, and a septic tank is usually the simplest and cheapest system to run. On the heavy clay of the Weald, they are often failed, because clay drains too slowly. On low lying ground such as Romney Marsh and the levels around Rye, the high water table usually rules a drainage field out. Replacing a failed drainage field explains the tests in detail.
The nearest water
A treatment plant can go where a drainage field cannot, because what it discharges is clean enough for a stream or ditch. That only helps if there is a watercourse that flows all year within reach. A ditch that dries out every summer does not count. And near a protected site, a new discharge to water cannot use the binding rules within 500 metres, so the plant may need a permit.
So the pattern is simple. Good ground points to a septic tank. Poor ground with a flowing watercourse points to a treatment plant. Poor ground with no watercourse points to a cesspool, because a cesspool discharges nothing and needs neither.
Space on the plot
A septic tank needs room for the tank and the drainage field at the required distances, which takes a good share of an ordinary garden. A treatment plant needs room for the unit and a route for the outlet. A cesspool needs only the tank, but a large one, at least 18,000 litres for two people plus 6,800 for each extra person, and it has to be within 30 metres of where a tanker can park. On a small plot, the space can decide the system before the ground does.
Power
A treatment plant needs a permanent electricity supply, running all day, every day. On an isolated site without mains power, that counts against it. A septic tank and a cesspool need no power at all.
How the house is used
A treatment plant depends on a steady population of bacteria fed by steady use. A holiday let that stands empty for weeks and then fills up, or a property occupied only at weekends, is harder on a plant than a family living there all year. A septic tank copes better with uneven use. A cesspool does not care how it is used, but every litre still has to be tankered away, so a busy household on a cesspool pays for it in emptying.
Access for the tanker
Every system needs emptying, a cesspool every few weeks, a septic tank about once a year and a treatment plant at least once a year. The building regulations expect a septic tank or cesspool to be within 30 metres of vehicle access. On a property at the end of a long track or down a narrow lane, a system that needs emptying less often has a real advantage.
The long run cost
Put it together over ten years rather than on installation day. A cesspool is often the cheapest to install and the most expensive to run, because of the emptying. A septic tank is moderate to install and cheap to run, as long as the ground suits it. A treatment plant costs most to install and adds electricity and servicing, but it can go on sites where a septic tank would fail. How much does a cesspool cost, how much does a septic tank cost and what a sewage treatment plant installation costs break those down.
Permissions, whichever you choose
Any new system needs building regulations approval, may need planning permission, and should meet the British Standard for its type. A septic tank or treatment plant must also meet the General Binding Rules or have an environmental permit. A cesspool sits outside those rules because it discharges nothing, but it must never leak or overflow.
Getting it right first time
Most of these questions are quicker to answer on site than on paper, and getting them wrong is expensive. We look at the ground, the space, the water and the access, and tell you which system genuinely suits the property, including when it is a cheaper one than you expected. Our new tank installations page covers the work, and do I need a sewage treatment plant goes deeper on that one decision.
KP Cesspool Services has emptied, serviced and installed all three kinds of system over twenty years, and you can read what customers say about that work on Checkatrade. Call 01233 720725, email kpcesspoolservices@hotmail.com, or contact us to arrange a site visit.
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