Thames Water outage: CEO Cathryn Ross explains why up to 13,000 people lost water for several days

Thames Water’s CEO, Cathryn Ross, has given a detailed update of what caused thousands of homes and businesses to be left without water for several days. The incident affected up to 13,000 people across seven postcodes with many having to resort to using water bottle stations.

Just last week water supplies cut out again for some in the Guildford area after weeks of issues. On Wednesday night (15 November) Zoe Nguyen posted on the social media platform X, formerly known as Twitter: “No water again in GU2 4 postcode. When can it be fixed? I’m sorry doesn’t do it!!! This is 3rd times without water in the last month - 7 days last time. How long it will take this time?”. Another user whose water supplies had also been affected posted on X telling Thames Water that its “management should be under police investigation”. 

MP Jeremy Hunt was demanding answers from the water company on behalf of his constituents. Ms Ross addressed a letter to him setting out three reasons why the water supplies ran dry and adding that the company will be happy to attend a public meeting to explain everything to those who were affected. The first reason given for the water outage was Storm Ciaran which Thames Water says “affected the power supply at Shalford, Netley Mill and Ladymead treatment works” on 2 November. It added that “without power the sites could no longer produce clean water so local reservoir levels dropped” and so this meant that a “relatively small number of customers” were impacted overnight.

Sites were back up and running the next day on 3 November but the problems continued. Thames Water said there was “an increase in turbidity” from the river sources supplying the Shalford works which caused the water to become more cloudy due to “stirred up sediments in the water". 

The company blamed this on the “heavy rainfall caused by the storm" adding that the change in turbidity led to a “failure of the treatment process" which had a knock on effect to “parts of our north and south west supply zones in Guildford.” By 4 November up to 13,000 people had been affected.

Thames Water said it restarted the Shalford works several times between 2 and 4 November and staff were “working around the clock to restore water supplies" but the ongoing turbidity “made it impossible to initially bring the works back into operation". On 5 November the company “completed an intensive operation to wash all treatment filters" which brought the works back online.

Over time, Thames Water said it slowly increased the “output of the site, which is not designed to be rapidly restarted taking care to ensure we maintained water quality standards.” Then on 9 November a motor failure at the Ladymead treatment works meant some customers in the GU1 and GU2 postcodes went without  water again. The company said “we sent a text message to customers and updated our website. The motor was replaced on Friday morning and water supplies returned alongside plumbers attending customers' properties where airlocks were reported.”

In the letter Thames Water outlines it will be spending £93.1m to improve the water infrastructure around Guildford and Godalming. The letter ends with an agreement to hold a public meeting to explain what happened. However, Ms Ross says this will likely not be until mid-December as this will be the time when the company will be better placed to provide answers.