Following a supply outtage which saw around 58,000 Southern Water customers left without water supply in the week before Christmas, CEO Lawrence Gosden has warned that similar incidents cannot be ruled out in future.

The warning comes in an open letter of apology from the water company chief published on 20 December acknowledging that Southern Water had let its customers down in its response to a water supply interruption due to a technical issue at its Testwood water supply works in Hampshire.

The community served by the Testwood water works has suffered similar interruptions in the past and the latest outtage was a repeat for many who live in the area. It was the single biggest water supply incident in the company’s history.

Testwood serves just over 70,000 homes and businesses - the consequences of its shutdown over a technical fault were “widespread and extremely rapid”.

Lawrence Gosden writes:

“I want to acknowledge specifically what we got wrong and what we’ll do about it.

“With 58,000 properties left without water, opening just one bottled water station on the first day was far from adequate. We had a lot of willing employees ready to staff more stations, but we and our partners failed to obtain sufficient quantities of bottled water. This left people queuing for hours, in cars or on foot. This fell far short of what the community needed.

“In addition, our more vulnerable customers – those on the Priority Services Register – were poorly served, having to wait too long for deliveries to arrive, and in some cases not receiving a delivery at all...

“In this note I also set out a commitment to compensate customers, costing £9.7 million, and I promise to review this incident thoroughly and learn the lessons.”

According to the CEO, there is always a degree of confusion over the Priority Services Register during an incident, as the company has to merge its lists with those of councils and the NHS. People also phone in to let the utility know that they or a relative are vulnerable. The list more than tripled inside a day to 20,000 households.

Lawrence Gosden promised customers Southern Water will “review very thoroughly what went wrong in the Testwood incident, and learn the lessons”, which includes “taking whatever steps are needed to ensure that we are better prepared for such incidents in future.”

The letter says that at Testwood itself over the next 7 years, Southern Water will invest a quarter of a billion pounds on improving the site for customers which will be spent on modern equipment, making Testwood efficient and resilient - far less prone to failure.

However, the Southern Water Chief warns:

“Unfortunately, similar incidents cannot be ruled out across the region in future. The new management team at Southern Water is determined to deliver improvements, and a turnaround for the company. But we have a lot of ageing infrastructure, like Testwood water works, which needs to be modernised or replaced. It should have been done a long time ago, but investment was squeezed as customer bills remained static for more than a decade. This badly needed investment is now coming, and is the main reason customer bills are going to rise significantly over the next 5 years.”