Do you need an interceptor tank for your next project, but are wondering how much you should expect to pay for one?

If you need an interceptor tank to manage and treat unclean water, one of your biggest concerns may be that your substructure may leak and let in potentially polluted water into the water course – which isn’t really an option.

Unfortunately, this is one of the risks when it comes to traditional methods of below-ground construction such as in situ concrete or glass reinforced plastic.

However, if you’re open to a more innovative and reliable approach that’s 100% watertight and may even come in at around the same cost, this blog’s worth sticking around for.

As a subcontractor who specialises exclusively in prefabricated steel substructures, I wanted to talk about how much you can expect to pay for a prefabricated steel interceptor tank, so you can get a better idea about what to expect and whether it’s a suitable alternative for your project.

TIP: Check out my blog: ‘What is Steel Prefabrication Below-Ground and How Does it Work?’ to find out more.

How much should an interceptor tank cost?

As a rule of thumb, all interceptor tanks are built to be bespoke to the building or project where they’ll be used, and the cost you can expect to pay will vary depending on the size and complexity of the project – along with other variables.

Since there is no set size for an interceptor tank, I’m unable to give you a typical price range. However, as I mentioned in a different blog, the typical cost of a prefabricated steel substructure (which can include interceptor tanks) is around £800 – £3,000 per sq. metre.

I know that’s not much help, which is why I thought I’d share this real-world example of an interceptor tank we built for Wide Lane, Southampton.

In this case, the interceptor tank we constructed using prefabricated steel came in at 2m wide x 4m long x 4m deep, for a cost of between £20,000 – £25,000.

In this case, we were approached by our client Winvic Construction, and the installation of the interceptor tank was a great success. All invert levels of the connections were installed off-site, and ladders and manholes were then refitted.

Due to the size of the interceptor tank, we were able to construct it in one piece in our factory. It was installed in just five days. A big bonus is that it’s 100% watertight and de-risked an extremely difficult activity the on-site construction team would have faced when building it in situ.

What other factors can affect the cost?

A big factor to take into consideration when building a substructure to be used as an interceptor tank, is that it’d have to be built using stainless steel.

The reason we’d have to use stainless steel is because the inside of the unit will be submerged in water. Using stainless steel will eliminate any rusting and corrosion problems – but this may mean your substructure will come out on the higher end of the price scale I mentioned above.

However, there are other significant benefits that can mean building with stainless steel can still save you money over other traditional methods such as in situ concrete, as I’ve outlined in this blog.

So, even if a prefabricated steel substructure might work out as more expensive than in situ, for example, you could still save 70 – 80% of time spent on-site; not to mention other factors such as long-term costs that come from water ingress and other issues.

TIP: Prefabricated steel interceptor tanks are welded together in an off-site factory environment, and are likened to the hull of a ship – meaning they’re 100% watertight. They’re also built to much tighter tolerances than in situ interceptor tanks.

Advice from a specialist subcontractor

The best advice I can give you is to explore all of your options, such as in situ, GRP, and prefabricated steel.

Remember, every option will have different benefits – some will be short-term benefits like lower cost, or less time spent on-site leading to a faster ROI at the end of the day. Others will be longer term, such as avoiding water ingress over time (important for an interceptor tank!).

I’d definitely put some serious consideration into the long-term risk of cracks, leaks and problems going forward, before selecting what looks like the most robust method for your project.


Thanks for reading. I really hope this blog has given you a better idea of costs with regards to prefabricated interceptor tanks and some of their benefits.  

However, if you want to more closely compare your options, and get a quote for your specific project that includes everything from design to installation, I’d recommend getting in touch with me directly.

Alternatively, if you have any questions, just leave me a comment below – I’ll be happy to help!