Stephen Eades – Do “storm overflows” operate in dry weather, and how would we know if they do? – Jul 2026

When Marinet campaigned in Parliament in 2020 on the Environment Bill (2021 Act) to secure reform of the water industry, Parliament agreed to make the water companies install monitoring equipment on all of their sewer overflow outlets. There are 14,403 outlets registered in 2025.

It seemed like a huge step forward at the time because, before then, there was no official monitoring system, and most of these overflow outlets were operating totally below the radar and no data on their use was being published. Of course, when operating they discharge raw sewage.

The monitoring now records every time the outlet is used, and for how long. Therefore, we know that collectively in 2025 these overflow outlets operated 291,492 times, for a total of 1,873,751 hours, with the average overflow lasting 6.4 hours. Moreover, half of the outlets (50.6%) operated more than ten times a year. We don’t know the volume of raw sewage that was discharged as the water companies aren’t legally required to measure this (see section 141DA of Part 5 of the 2021. Env. Act). Nationally however, 1.8 million hours of raw sewage dumped during the year into our rivers will be a great deal of sewage, and will cause serious pollution.

As it happens, 2025 was a ‘dry year’ weather-wise. 2024 was a ‘wet year’ and, as a result, these overflow outlets operated more often. In fact, 450,398 times, for a total of 3,614,428 hours, with the average overflow lasting 8.0 hours. Also, 61% of the overflow outlets operated more than ten times during the year. In a wet year the sewer system is under much greater pressure, and so the overflow outlets discharge more raw sewage to prevent the system being overloaded and flooding homes and streets.

Whether the year is ‘wet’ or ‘dry’, the high level of raw sewage being discharged reveals the massive the under-capacity in the nation’s sewage treatment system and, equally importantly, the failure of the water companies to invest to correct this. As the figures show, there is a great deal of sewage pollution in England today, and the public health risks that we are running are a growing cause for concern.

Amazingly, the figures above are not the whole story. There are around a further 6,000 emergency overflow outlets at the sewage works themselves, and they are not included in the above figures. Only about a quarter of these overflow outlets have monitors fitted, so we don’t know how often they are used or for how long. Moreover, under current plans it is going to be ten years before all the rest of these emergency outlets at sewage works have monitors fitted. You might reasonably ask, why not fit the equipment now, and not over the next ten years, so that we have an idea about much raw sewage is going out from these overflows?

There are other shortcomings too. For example, this blog is being written on 24^th July 2026 and there has been virtually no rainfall during the month across England. In fact, average rainfall has been 1mm and just 3% of the long-term average. Last year, in July 2025, England averaged 58mm, or 89% of the long-term average. Therefore, this July, you would imagine that not a single storm overflow would be operating.

However, you’d be wrong!

We know this because there is an online site which does up-to-date monitoring of the water companies. It is WaterWatch, founded in 2026 by Daniel Walls, a sixth-form student. He is the website’s sole developer, and the online platform he runs has no corporate structure, no investment, and no agenda beyond making the data genuinely understandable. It monitors all the water companies and provides an up-to-date-picture of the performance of their sewage overflow outlets – see the data on each company.

Whenever you go to the WaterWatch site and look up a particular water company, you’ll find out how many of the company’s storm overflow outlets have been operating during the last 48 hours. For example:

13 and 14^th July 2026.

Source: Water Watch 14th July: https://water-watch.co.uk/companies

21^st and 22^nd July:

Source: Water Watch 22nd July: https://water-watch.co.uk/companies

Therefore, the reality is that around 1% of all the storm overflow outlets in England are operating on any particular day regardless of the weather e.g. even when there is zero rainfall anywhere. Why?

The answer is that that there are around 2,200 sewage works in England operated by the water companies (2022 data) and that a significant number of them, perhaps between 1% and 2% (around 40 sewage works), do not even have sufficient capacity to treat all the sewage arriving on a rainless day. As a result, they have to dump raw sewage from somewhere downline in the sewer network that feeds them to prevent them from overflowing. And, don’t forget, every sewage works has an additional overflow outlet at the sewage works itself that can be used if necessary – but three-quarters of these additional outlets have no monitoring equipment fitted to them, and no data about the use of any of them (i.e. all of the 2,200 works) is published.

When, in 2022, Marinet surveyed the size of the sewage works in England in terms of their capacity to treat all of the sewage arriving at them during normal weather conditions i.e. including days when it rained, Marinet found that there is massive under-capacity in the nation’s sewage works.

Government requires, since 2018, that every sewage works is able to treat a volume of sewage that is equivalent to three times the volume that arrives on a day with dry weather. This is known as the ‘dry weather flow’ (DWF) and so every sewage works should have treatment capacity equal to 3DWF. Extra capacity (i.e. beyond 1DWF) takes the form of storage tanks that collect the extra sewage on wet days, and then feeds this extra sewage into the treatment process once the rain stops. As it takes only 12 hours to treat sewage through all of its treatment stages from start to finish, having treatment/storage capacity equal to 3 dry days flow is adequate to ensure that all sewage is fully treated, except during exceptionally stormy weather.

Marinet’s 2022 survey found that virtually no sewage works in England has treatment capacity greater than 1.5DWF, i.e. no works has more than 50% of the legal capacity that is required, and that the whole sewage treatment system in England is operating at between1DWF and 1.5DWF. In other words, there is massive under-capacity in the nation’s sewage works, none can meet the legal standard of 3DWF, and as a result raw sewage is being dumped routinely into our rivers – and even on dry days by those sewage works that do not even have 1DWF capacity.

So, the water company owners have been routinely taking money out of their companies in the form of dividends every year, despite knowing that the company they own and are required by law to operate to a clear legal standard is failing to do so, and Government has been allowing this abuse, in fact illegal conduct, to carry on without any serious enforcement action.

The result is that our rivers and coastal waters are routinely polluted by raw sewage.

Government now says (Environment Act 2021) that a Storm Overflow Discharges Reduction Plan exists that the companies must implement in full by 2050 and that this will ensure at sewage treatment works will have adequate (3DWF) treatment capacity by 2025. However, it will take 25 years to deliver! And, guess who is paying for it?

The money is not coming from the owners of the water companies. All of the money is coming from the public by continual annual increases in the water bill for the next 25 years! So, the owners of the water companies contribute effectively nothing, continue to take their annual dividends, and at the end of 25 years they will own water companies that are ‘legally compliant’, all paid for by the public!

Meantime, our rivers and coastal waters continue to suffer serious sewage pollution, and we run a very serious public health risk – see the recent Marinet blog by Brian Morgan on this subject: Is the incidence of some fatal diseases linked to untreated sewage discharges?

When will government in England, indeed throughout the whole of the Kingdom, begin to perform its most basic of duties – to ensure that all human sewage is treated properly?

As the traditional rhyme puts it: Will it be this year, next year, sometime, or never?

What is certain, there is a great deal of work to be done – and, it needs to be done now.