How Weather Affects Cesspools and Septic Tanks

At KP Cesspool Services, we see first hand that problems with private drainage are rarely random. They follow the weather. A cesspool, a septic tank and a treatment plant all sit in the ground, and the ground changes through the year. Wet winters fill old tanks with groundwater and drown drainage fields, summer droughts crack clay and pipework, and storms take out the power a treatment plant runs on. This guide goes through the year and explains what each kind of weather does, which systems it affects, and what you can do about it.

Wet winters and a rising water table

Winter rain is the biggest weather problem for private drainage in Kent and East Sussex, because so much of both counties is either heavy clay or low lying ground with a high water table.

For a cesspool, the risk is water getting in. A sealed tank in good condition is unaffected, but an older brick or concrete one with a cracked wall, a failed joint or a loose cover lets groundwater and rainwater in. The tank then fills far faster than the household alone would explain, and you pay to have clean water tankered away. If your tank needs emptying much more often in winter than summer, that is the usual reason.

For a septic tank, the risk is the drainage field. It can only soak away liquid into soil that has room to take it. When the ground is saturated, or the water table rises close to the bottom of the field, the effluent has nowhere to go. It backs up into the tank and the house, or surfaces in the garden. That is why the British Standard for drainage fields measures the ground against its seasonally highest water table, not its level on a dry day. Replacing a failed drainage field explains what a field needs.

For a treatment plant, wet ground matters less to the treatment itself, but a submerged or silted outlet stops it discharging, and groundwater can get into an older plant's chambers just as it does a cesspool.

When the garden floods

If floodwater covers the tank or the drainage field, stop using water in the house as far as you can. A flooded drainage field cannot take anything, and every flush pushes sewage back towards the house.

Once the water goes down, have the system looked at before you rely on it again. A cesspool or septic tank may be full of floodwater and silt. A treatment plant's electrics may have been under water and should not be switched back on until they have been checked. And a lightweight plastic or fibreglass tank should never be emptied while the ground around it is still waterlogged, because the water pressure can push an empty tank up out of the ground.

Frost and freezing

Hard frosts are less of a worry than people expect. Tanks and buried pipes are protected by the ground around them, and the waste water going into them is warm. The weak points are pipes that are exposed above ground or near the surface, and the blower or control box of a treatment plant if its housing is damaged and letting cold air and damp in. Keep pipe lagging in good order and the blower housing closed.

Summer drought

Long dry spells cause a different kind of damage, especially on clay. Clay shrinks as it dries, and the ground can move enough to crack old clay pipes, open up joints and shift a pipe out of line. The first sign is often a blockage in a pipe that has never blocked before, or a smell in the garden in late summer. What causes blocked drains and tanks covers the rest.

Warm weather also makes smells more noticeable. That is not always a fault, but a strong or persistent smell is worth investigating. What to do if you notice smells helps you work out the cause.

Storms and power cuts

High winds bring down branches and blow leaves into gullies and inspection chambers, which can block the pipes leading to a tank. A quick look at the covers and gullies after a storm saves a callout later.

Storms also cut the power, and a treatment plant stops treating without it. The building regulations expect a plant that depends on power to keep working adequately for up to six hours without it, or to have a backup supply, so a short cut is rarely a problem. After a long one, keep water use down for a day if you can and watch for the alarm.

Autumn leaves

Leaves are a nuisance for any property with yard gullies or rainwater drains. If a blocked surface water drain overflows into the foul drainage, it can send rainwater into a cesspool or septic tank, and that water has to be paid for or soaked away. Clearing gullies in autumn is cheap insurance.

A year round plan

Most weather problems are easier to handle on a system that is already in good order. Empty a cesspool on a schedule set for the wettest months rather than the driest, so it is never close to full when the ground is at its worst. Have a septic tank emptied and looked at before winter, so the drainage field is not taking sludge as well as rain. Keep a treatment plant serviced, with its alarm working. And keep rainwater out of the foul system altogether. Downpipes and yard drains should go to a soakaway or a surface water drain, never to the tank.

Your legal duties do not change with the weather

A septic tank or treatment plant still has to meet the General Binding Rules in a wet winter, and a cesspool still must not overflow. If bad weather causes sewage to reach a ditch or the surface, the owner is responsible, and the Environment Agency can take action. Dealing with a weather problem quickly is the best protection.

Help when the weather turns

Our cesspool emptying, septic tank servicing and emergency callouts cover Kent and East Sussex day and night. KP Cesspool Services has over twenty years' experience across both counties, and you can read our reviews on Checkatrade. Call 01233 720725, email kpcesspoolservices@hotmail.com, or contact us.