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Severn Trent cautioned for supplying water 'unfit for human consumption'

Severn Trent Water has been cautioned by the Drinking Water Inspectorate (DWI) for supplying water that was 'unfit for human consumption'.

The caution relates to an event in March 2016 when consumers in 3,700 properties were advised by Severn Trent not to use their water for 26 hours due to elevated levels of chlorine.

The event occurred at Castle Donington Service Reservoir, Derbyshire, and involved the contents of a sodium hypochlorite storage tank draining into the inlet main to the service reservoir. The DWI’s investigation has concluded that this serious event “was avoidable, and that there were a number of missed opportunities to identify and rectify the problem before the event”.

Severn Trent, which admitted supplying water unfit for human consumption under Section 70 of the Water Industry Act (1991), isolated the chlorine dosing equipment at the service reservoir, and flushed the supply network to remove the affected water. However, the incident resulted in the supply of unwholesome water to some consumers, some of whom rejected the water supplied to them.

The company has replaced the chlorine dosing equipment at the service reservoir site to prevent a recurrence of the event. It has also audited more than 190 similar secondary chlorine dosing rigs currently operational across its asset base, and has instigated corrective actions as necessary.

Other actions taken to further mitigate the risk of a similar event occurring at other sites include a competency assessment of all staff involved in operational activities at service reservoirs and at chlorine booster stations; a review of chlorine booster station alarm settings and telemetry stations for reliability; changes in procedures; a review of the use of GIS systems to more accurately and rapidly identify areas affected in any future event scenario; and a review of alternative supply management arrangements. 

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