Network Turbidity: Clean, Clear and Compliant

Tracing its roots back to the Caterham Spring Water and the Sutton and Cheam Water companies, SESW have been supplying water to residents of the Sutton and Surrey areas for over 150 years.

They currently cover 835 km2 (322 square miles) supplying 670,000 customers and 282,000 properties. Whilst being one of the smaller water utilities in the United Kingdom, the challenges they face, and the solutions they provide, are as big as any of those in the industry.

To meet demand SESW have 8 large treatment works, 7 abstracting from aquifer boreholes as is typical of southern England and Wales. Unlike other utilities however, SESW soften their borehole abstracted water prior to distribution. Whilst this helps to prevent future lime scale build-up and protect customer’s property, it does little to abate the historical calcite deposits lining the network mains and communication pipes. These deposits can be disturbed by high flow rates, causing significant turbidity issues if not dealt with properly.

Turbidity Challenge

Last year SESW experienced 392 customer contacts for taste, odour and turbidity, missing their target of 350. On a monthly basis this equates around 33 reported contacts against their target of 29.

The significant number of these events are the result of white and turbid water, stemming from the historical calcium deposits, which can become mobile at flow rates above 10 L/sec. Typical events that cause elevated flow rates are:

  • Bursts
  • Illegal unauthorised standpipe use
  • Network servicing activities.

Of those 392 customer contacts, only 60 were the result of network servicing related activities.

Prosecuting illegal standpipe users and ongoing investment in at risk mains will continue to reduce reported water quality events however these are generally medium to long term activities, and SESW already have some of the lowest burst rates in the country.

In order to quickly get back on track and meet their customer contact target, it was important for SESW to tackle the 60 events where they could control the outcome.

The biggest challenge to overcome was quickly and accurately establishing the turbidity of the mains water before returning it to service. This had been done visually by the network service teams with a sample collected for lab analysis the next day.

However, with a consent of 4 NTU it was near impossible to be sure if the visual assessment would match the laboratory results – especially when operations were occurring at night.

The image above shows how close a 0.05 NTU and 20 NTU standard appear to the naked eye.

The result of this difficult visual detection is increased customer complaints and the network team having to revisit serviced mains to carry out more flushing.

Small Investment – Big Payback

Damian Crawford (Wholesale Services Manager for Networks) decided to equip the network team with portable turbidity meters to allow them to objectively and confidently assess when a main can be reconnected. After trying meters by various manufacturers the Palintest Turbimeter demonstrated the best blend of laboratory and field performance in a package that was quick and easy to use.

Since introducing the Turbimeter in its network teams, Damian saw a 15% monthly reduction in customer contacts.

Focussing on water quality events from network servicing related activities, he projects that, based on current monthly rates, they expect to hit around 16 events this year, down from 60 last year.

All of this now means SESW are currently on track to meet their annual target, with an average of 28 monthly customer contacts against their target of 29. The impact of this is not just an improved customer experience but also increased compliance, fewer water quality penalties and improved service incentive mechanism (SIM) ratings, which ensure a minimal payback time on the investment in the Turbimeter roll-out.

More than Just Numbers

The benefits of rolling out the Turbimeter extend beyond performance numbers and have positively impacted the day to day responsibilities for the Customer Field Managers and Engineers, who have experienced significant time and efficiency savings.

“The instrument is easy to use, and getting a result takes clicking one button. It saves a lot of subjective debates stood in the rain at 4AM” – Adrian Palmer, Customer Field Manager at SESW.

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