Report on sewage clean-up costs shows why a systems approach is vital

Built Environment, Energy & Climate Change, Natural Environment, Processed Water

None of the options presented in the newly published Storm Overflows Evidence Project (SOEP) are cost beneficial. Of course not! Sewage pollution – and the solutions to it – has to be dealt with systematically and not just through water companies.

Some of the numbers in the report are eye-watering. Media over the past few days has reported costs to “fix” the problem of anything up to £660bn, to £3.9bn for tackling just the worst performing overflows. There’s been a lot of criticism of the uncertainties and range in possible costs – presented as government not having a clue. SOEP hangs some detail on that range.


The SOEP used modelled hydraulic data from water companies on their expected discharges, from their latest planning rounds. It did this because it wanted to understand the volume of water that might need to be dealt with to significantly reduce overflows.

It didn’t use the Environment Agency’s observed data that is being so widely scrutinized by the public – something that will undoubtedly irk campaigners. This data only measures frequency and duration, not quantity though. So, if you’re trying to understand how much you need to increase sewer capacity it won’t help.

The solutions modelled include increasing storage in sewers and treatment works through more storm tanks in the network, or using sustainable drainage (SuDS) including tree pits, raingardens, water butts and storage basins to stop a proportion of surface (rain) water entering combined sewers.

Wider benefits?

The study showed it’s cheaper and easier to fix the problem by just building more concrete storm tanks and putting in bigger pipes. Solutions that deliver no additional benefits.

It acknowledges that wider benefits from SuDS – from air and quality urban habitat improvements to mental wellbeing or managing flash floods – will vary considerably depending on where they’re constructed. As a national level look, local opportunity to maximise these benefits is lost from the picture.

The report also notes that costs can be reduced significantly by taking the opportunity to put in sustainable drainage at times when other street works are happening, or in partnership with other bodies such as local councils to manage other local pressures like flooding or air pollution.

The authors point to many reasons for the current high levels of discharge and inadequate capacity and condition of sewers.

These include blockages caused by people putting wet wipes and fats down the drain, groundwater entering sewers though cracks and holes in sewer pipes, or the effect of local, intense rainfall associated with climate change. But tackling these – at source – aren’t factored into the costs or benefits.

So the fact there is such a wide range of uncertainty in the figures shouldn’t be a surprise. This is a first, high-level look at the problem. A problem that will need to be tackled overflow-by-overflow, in the best way for each. Context will give clarity on cost.

Collaborate to unlock opportunities and efficiencies

But to keep costs as low as possible we need to hit all the contributors, and do it in a joined-up, systematic way.

Why spend £50bn, say, on extra storage when we could reduce that bill by choosing not to chuck wet wipes and fats that cause blockages down the drain as part of a more systematic approach – for free?

Why do one SuDS scheme somewhere to tackle storm overflows and another down the road to deal with surface water flooding when good link-up between a local authority and water company could hit two birds with one stone and share costs? But funding frameworks aren't really optimized to enable this co-delivery.

New water company Drainage and Wastewater Management Plans are supposed to drive that kind of strategic, collaborative approach with other bodies. But in practice it can be challenging to bring everyone to the table and work together effectively, everywhere, because of lack of capacity and skills in the right places.

Are we going to stop putting additional load on sewers from new housing, roads and other development? Schedule 3 of the Flood and Water Management Act 2010 (yes, from a decade ago) was designed to do this, but considered later to be a ‘burden’ on developers and not implemented. Instead, a half-hearted fudge of an approach exists which will result in the same kind of under-delivery as has befallen sewer networks.

Schedule 3 is under review at the moment but will surely face opposition from old-school orthodoxy around regulatory burden and the environment.

It was the right thing 11 years ago. It’s the right thing now.

So what does SOEP tell us? That whatever way you slice it, sewage pollution from storm overflows isn’t going to be cheap to clean up. But also that we shouldn’t look at this as just the water companies’ problem to fix.

Sure, they have an awful lot to do. But, looking at this problem - or tackling it - through a water industry lens absolutely won’t give us the best outcomes, or the best bang for our buck. It would just mean a lot of money gets spent in one area while the range of exacerbating factors continue elsewhere, and likely get worse.

We can sort this issue out whilst also making our towns and cities far nicer, cleaner, greener places to live. Places that are more resilient to the floods and heatwaves that are coming more often with climate change. That’s quite a raft of fringe benefits.

There are all kinds of pots of money out there to deliver these win-wins. If we can join them up we can get better progress, quicker - something SOEP acknowledges but doesn't dig into. At CIWEM we’re working on mapping out how we can do just that.

Water Minister Rebecca Pow said in the Commons recently that this is a cross-government issue. Too right – environment, housing, transport and business departments all have a role.

All had a role in ensuring infrastructure was delivered in a way that failed to take proper responsibility for the health of our rivers and wider environment. All now need to come together and be part of the solution.

Alastair Chisholm

Director of Policy, CIWEM

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