Power pollutions: Is the water sector doing enough to protect itself?
Water companies have reported that over 200 pollution incidents last year were caused by power issues. The data raises thorny questions over resilience, accountability, and how well the sector is working with the grid.
By Ella Jessel, water editor
Power pollutions: Is the water sector doing enough to protect itself?
Water companies have reported that over 200 pollution incidents last year were caused by power issues. The data raises thorny questions over resilience, accountability, and how well the sector is working with the grid.
By Ella Jessell, water editor
Earlier this year, Southern Water’s control room was alerted to a power failure at one of its treatment works during a nighttime storm. Staff drove a backup generator to site in 90 minutes, but it was too late to stop a sewage spill. “The additional factor of heavy rain meant that there wasn't an hour-and-a-half's worth of storage within our network,” explains Chris Perkins, the firm’s head of pollution performance.
The incident is one of hundreds of power-related pollutions reported by water and sewerage companies in England and Wales last year. Their pollution incident reduction plans (PIRPs), a new statutory requirement this year, show 226 incidents caused by power failures at treatment works and pumping stations in 2025.
The data, which is self-reported and disputed in some cases by electricity networks, shows that more than half were attributed to “root cause” failures on the grid. These were mostly due to weather conditions, though 2025 was a year with fewer named storms than the year before.
It comes as the frequency of extreme weather events is pushing the risk of interdependence and resilience to climate change up the agenda. Trade bodies Water UK and the Energy Networks Association (ENA) recently held workshops in a bid to drive collaboration between the two sectors on the issue.
Yet there is still tension over where the responsibility rests. While water companies might have identified power as a root cause, the incident will still be logged as a water company pollution. The Environment Agency has made it clear it expects water companies to be resilient to all weather events.
In response to the PIRP data, Alexandra Howe, the ENA’s director of policy and external affairs, said any suggestion that power outages are a significant cause of water pollution events is “wrong” and risks misrepresenting who is responsible for operational resilience.
Meanwhile, Water UK has previously backed arguments made by individual companies, such as Northumbrian Water, that the responsibility for risks beyond its control should not be placed on water customers or companies.
Source: water companies' pollution incident reduction plans for 2025
Storm hotspots
Storm events and high winds increase the potential for power supply disruptions which, as Southern Water’s example shows, can set off a chain reaction resulting in pollution incidents at pumping stations and wastewater treatment works, or a loss of water supply.
Data from the PIRPs shows that all 10 water and sewerage companies reported incidents linked to power issues, but there was big variation by region. The water firms that cover the largest geographical areas reported some of the highest numbers of power-linked pollutions, including United Utilities (66) and Anglian Water (35). Wessex Water also reported 42 power-related pollutions, amounting to over half of pollution incidents at pumping stations in 2025. Northumbrian Water reported 27.
United Utilities, which also reported 66 power-related pollutions in 2024, said it was seeing an increasing number of storm-related power interruptions. The firm said 12% of its total wastewater pollutions for the year happened during Storm Éowyn in January 2025.
One of the utility’s main pressure points is Cumbria, which contains the Lake District National Park - a very rural area supplied by lots of overhead power lines with plenty of trees. According to Tom Lissett, United Utilities bioresources and green energy director, the firm’s pollution data shows that more than half of its pollution events caused by power disruption in 2025 were in this area.
“When we have storms, we can experience blackout-like power disruption which can obviously impact on our service,” he says. “Those overhead lines can also be impacted by 'brownout activity', where the power remains on, but surges on rural networks can disrupt our assets.”
Lissett says the company is carrying out a range of projects to boost resilience. Ahead of winter it has been surveying every site in the Windermere catchment to protect its sites from power disruption. This has resulted in significant investment in backup power such as batteries, generators, and Uninterruptible Power Supplies (UPS), devices which provide emergency battery backup power when the main power fails.
Some water companies are installing permanent backup generators at critical sites, but not all treatment works need permanent backup power, and due to the cost of installation water companies have to prioritise based on the risk. Many water companies, such as Thames Water, are investing in fleets of mobile generators which have the benefit that they can be moved around depending on where they are needed.
Water companies are training staff to deploy mobile generators in an average of two hours, but in these extreme weather events multiple sites can lose power at the same time, meaning it can be difficult to respond in time.
Proportion of pumping stations that would spill before a mobile unit could restore power, according to a consultants' report.
The cost of installing permanent backup power at 84 Northumbrian Water sites. Ofwat rejected the bulk of the investment
Northumbrian Water appealed to the Competition and Markets Authority (CMA) last year after Ofwat turned down most of its request for £59 million to install permanent backup generators at 84 sites. Ofwat had queried its requirement for permanent generators over the cheaper mobile units, but Northumbrian countered that these arrive too late in storms. It cited a consultant’s study saying 91% of pumping stations would spill before a mobile unit could restore power.
Perkins explains that one of Southern Water’s first big power projects was to invest in auto pump resets, so that it does not have to get staff to site for a manual reset if a power dip trips the electrics. Over 1,000 pumping stations have now got auto reset capability, and it is now working on standby generation in high-risk areas.
“We are exploring battery energy storage systems (BESS), which can give you several hours of running if you suffer a blackout,” Perkins says. “But they also really help with the voltage depressions because they buffer out the fluctuations that we see.”
Southern has also invested in monitoring technology which looks at the incoming power supply to gauge where sites are having lots of depressions or spikes or outages. “It's the same technology that SSE and UK Power Networks use. So we're able now to talk the same language with the electricity distribution operators (DNOs).”
Collaboration ‘patchy’
While water companies are working on resilience projects, there will always be a risk of an outage. "We can't control when the power stays on, and the DNOs aren't regulated and funded by Ofgem to provide an ‘always on’ service,” says Lissett. “From a system perspective, there’s a gap and therefore always a risk that we could have a disrupted electricity supply."
Lissett says United Utilities has a strong relationship with SP Electricity North West (SP-ENW), and it has monthly meetings to discuss hot spots in the network, aligning investment and asset plans and issues like winter preparedness. “These relationships and this collaboration are critical,” he says. “Ultimately, we are providing essential services to the same customers, and we all want to avoid a situation where they have lost both electricity and water supply at the same time.”
The two utilities are working together in areas including improving communication on network issues, co-ordinating responses and critical treatment works sites flagged on the operator’s control system to help with real time decision making and control of the network.
Mark Mercer, licence director for SP-ENW, says the conversations have been “really valuable” and it was continuing to explore new ways of working. “We share the same North West customer base with United Utilities and recognise the value in working together to drive excellence for our customers,” he says.
One of the issues for water companies are “brownouts”. Unlike a blackout, a brownout is a temporary, partial drop in voltage in an electrical power system. These dips in power often remain within a DNO’s statutory limit, meaning they might not be logged as an outage. Yet according to the water companies, their treatment works will still be affected.
“Definitely what we're seeing is our more modern equipment is susceptible to these depressions within that statutory limit,” says Perkins, adding these can cause plant asset failures, trips, and control systems not responding as they should.
Perkins says the company has seen an increase in brownouts, which is down to a number of factors including stresses on the network from the South East being a growth area, and the impact of switching to smaller renewable units.
SSE declined to comment. A UKPN spokesperson, meanwhile, said it was "working closely" with Southern Water to better understand their resilience issues, including data sharing, and that outage volumes can fluctuate from year-to-year, often depending on the weather.
However, it added that initial data recently provided by Southern Water indicates their current conclusions around DNO power supply outages are "not sufficiently accurate" and "need further validation."
UKPN added that brownouts are milli-second duration voltage dips that infrequently occur on all distribution systems and are universally not classified as power outages. "Industry standards exist which require user equipment to ride through these milli-second events. However, as stated we are working with Southern Water to see where we may be able to help."
"Overall, UK Power Networks and Southern Water are having proactive meetings to understand their resilience issues and validate their reporting process."
But while collaboration is happening in pockets, there are regions where things are more challenging. According to Lissett, who attended one of the recent workshops hosted by Water UK, there is a “mixed picture” across the UK in terms of power resilience and water company to DNO relationships.
“We have spent a lot of time building a shared understanding across the North West and I can see other regions doing the same but there is clearly more that we can do working together towards a common goal,” he says.
Liability tensions
One of the tensions is around responsibility for pollution incidents. According to Hannah Bloomfield, an academic at Newcastle University working on climate resilient energy systems, this is a key issue in the discussion around cascading events in the utility sector. “It’s really hard to find evidence on where the liability sits for these events, and without seeing the timing of outages and potential causes in DNO data, it is hard for water companies to directly attribute these pollution incidents to the weather-induced faults,” she says.
On the energy side, the ENA says the UK has one of the most reliable and resilient electricity networks in the world, and no system can provide absolute continuity of power. “Owners of critical national infrastructure must have their own resilience strategies and business continuity plans in place,” adds Howe.
Yet water companies have been pushing back, and have argued they are not given enough funding to protect themselves against third-party failure. In its PR24 price review, Ofwat allowed over £1.5 billion for resilience, more than double the previous period. That includes £300 million for climate resilience, particularly against power interruptions and flooding.
Northumbrian’s ask of £59 million for generators for PR24 was reduced to £4.5 million by Ofwat for six sites with repeated power-related pollution, plus about £7 million from the sector-wide uplift for resilience. This was later bumped up to £15 million by the CMA.
This was despite Northumbrian arguing that its patch suffers some of the worst effects of storms, and criticising the “stark” disparity in how resilience is funded by regulators. It said that after Storm Arwen in 2021, Ofgem provided efficient investment to energy networks to address extreme weather. Whereas Ofwat rejected its “sensible proposals” for backup generation on its treatment works. Both regulators were approached for comment.
The water firm also criticised the lack of a coordinated cross-government approach or collaboration between regulators for when power failures hit pumping stations, and questioned whether water customers and companies should “pay the price for a lack of resilience in energy networks”.
Water UK declined to comment, but it has also made similar arguments. Its response to the draft PR24 determination, submitted in 2024, said that water companies and customers should not hold responsibility for outages at treatment works, stemming from “failing power distributors”. It has since called for legally-binding resilience standards, a measure the Starmer administration committed to introducing.
At Southern Water, where the backup generator arrived too late for the spill, Perkins says it's not enough to rely on “response alone”. The company is expanding its standby generation and has seen a “step change” in its engagement with DNOs. “We're not going to be able to solve this on our end, and they're not going to be able to solve it on their end. We need to work together, and that's what we're starting to do."
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These debates are only likely to intensify as the UK sees more extreme weather events in both summer and winter. Bloomfield adds that one of the biggest challenges in resilience are the emerging weather patterns at the moment where summer drought is followed by storms, as well as the country's increasing reliance on electricity.
“These conversations between utilities do need happen right at the top level, and there needs to be a little bit more openness between all these players,” he says. “Because things are going wrong and there are lessons we can learn from it.”
