Southern Water is proposing an investment of £63 million to strengthen the resilience of its Hardham Water Supply Works following loss of water supply to some 25,000 customers in areas of Sussex in May 2023. 

The water company has set out its proposal in a summary report of the findings of an internal investigation after Hardham Water Supply Works was automatically shut down late in the evening on Friday 12 May when sampling highlighted a change in water quality. 

Around 25,000 homes and businesses were affected at the peak of the incident, although supply was restored to 22,500 properties by Monday 15 May. All remaining customers’ supplies were restored a day later.

The report says Southern Water is continuing to invest in upgrading its critical water sites and has put a detailed four-site improvement strategy in place which is focussed on upgrading its largest and most critical water supply sites.

The water company has proposed a £63 million spend on improving the resilience of Hardham Water Supply Works after 2025, subject to confirmation by Ofwat following the 2024 price review process and is “in discussions with regulators to make this happen as quickly as possible.” The improvements would reduce risk at Hardham by 30% by 2025 and by 80% by 2033.

Tim McMahon, Southern Water’s Water Director, said:

“We are very sorry to those who were impacted by this disruption. We have carried out a thorough internal review into what happened, as it is vitally important we are transparent with customers when we fall short of expectations.  

“Our investigations found that the water entering Hardham from the nearby river and storage reservoir was unusual in that it contained more sediment and impurities than normal, which caused difficulties for our treatment processes.

“Unfortunately, there is no way of knowing the exact source given the number of potential factors, such as agricultural and industrial run-off, but we have fully reviewed our own on-site policies and procedures so we are as prepared as we can be if this were to happen again.”

The investigation found that the probable cause was an unusual peak in turbidity in the raw water entering the treatment works from the river and storage reservoir, leading to treatment challenges – in particular, chlorine dosing issues.

The report says this affected the clarification, filtration and disinfection treatment processes on site - made worse by a blockage of the main chlorine dosing system, because of calcification build up in the water softening system.

Southern Water says it took immediate action and has since reviewed the policies and procedures at all its treatment sites. In addition to site-specific ongoing improvements now being put in place on site, the water company is also implementing the following measures across its water treatment assets:

• review of control and procedure for clarification and filtration.
• review of criticality of softening.
• immediate instruction to ensure that Sodium Hypochlorite with Calgon is used at all water
• supply works
• check of all static mixers and dose injectors
• review of chlorine dosing systems
• inspection, testing and remedial work on both contact tank cells to investigate bubbling of tank
• wall lining
• assessment of the raw water transfer main (to be exposed) so trials can be carried out on different flows to see if there is a leak
• acceleration of proposed improvements to the online monitoring and control system
• fast track issue of updated site check lists
• review of all documentation on site
• method of recording alarms for handover to be developed
• individual filter logs to be introduced.

The final report summary includes a full list of recommendations, actions planned and those already completed. Click here to download the summary report