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Septic tanks vs. sewage treatment plants - what's the difference?

Sam Warren's Photo
Written by Sam Warren

Ok so 'septic tanks vs. sewage treatment plants' might not be much of a battle worth watching, but if you have a property with an off mains drainage system - or are thinking of buying one - it's worth knowing the difference.

This is all the more important bearing in mind the change in legislation to do with septic tanks which takes effect in 2020. This will make certain types of drainage systems involving septic tanks no longer legal. So knowing whether you have a septic tank or a sewage treatment plant lurking underground at your property could save you a whole lot of trouble and possibly a weighty fine.

If you're buying a property, it's really important too - buy a house without knowing whether it has a septic tank or a sewage treatment plant at your peril, as you could find yourself on the hook for a big fat bill to upgrade your system in 2020.

So, what are the main differences between septic tanks and sewage treatment plants?

First of all, let's take a look at an example of each:

Blog septic Tank diagram
Septic Tank
Sewage treatment plant diagram
Sewage treatment plant

Here are the main differences between the two

  • Sewage treatment plants have mechanical components, which means that they need a permanent electrical supply to operate. There are no such components in a septic tank, and so it operates without a power supply.
  • As you can see from our example diagrams above, a typical septic tank has two 'zones', whereas a sewage treatment plant typically has three.
  • A sewage treatment plant provides treatment of the waste, whereas a septic tank simply separates it - this means that the waste water that leaves a sewage treatment plant is cleaner than what leaves a septic tank. You still might not want to brush your teeth with it, but it's certainly a lot more environmentally friendly.
  • As a result of the cleaner waste water that leaves a sewage treatment plant, you can discharge the waste water straight to a local watercourse. There are a lot of properties out there which currently have a septic tank that discharges to a local watercourse (instead of to a soakaway system or drainage field). As of January 1st 2020, this is no longer legal. What does this mean to you? If you own a property with this drainage system, you must upgrade it by that date. If you are selling a property with this system in place before 2020, you must upgrade it before selling. If you are buying a property with a septic tank discharging to a watercourse and this hasn't yet been discussed - don't! Until agreement has been made about upgrading the system. Click here to find out about our Home Buyer Drainage Surveys and the peace of mind you get from knowing exactly what you are taking on.

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Sam Warren's Photo
Written by Sam Warren

Sam's career prior to UKDP was spent in the marketing and service industries, so she is focused on making sure we look after our customers – and getting the UKDP message out there! Sam has overall responsibility for business operations and for delivering the best customer service we can.

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