First stage in costing water leakage

The county of Staffordshire in England is renowned for pottery – and very close to Stoke on Trent, the heart of the pottery world, lies Cheadle, a town of about 8000 people. It’s an old market town and was previously supplied by a small private water company which had been established in the early 19th century. The water supply was from boreholes, and in recent years the combination of limited resources from the boreholes, growing customer demand for water and high levels of leakage from the aged distribution system had resulted in a very poor level of service to customers.

Severn Trent Water took over the Cheadle Waterworks Company in 1997 and put into effect substantial improvements. The main intention was to benefit the Cheadle customers – but at the same time we realised we had an opportunity to gain some valuable information about the costs and effects of distribution system improvements.

Because Cheadle was self-contained, we were able to measure the effect of the changes we made. One of the key features of what was planned for Cheadle was the wholesale renewal of the distribution system. At the time of incorporation in the Severn Trent supply system, Cheadle had a leakage level of over 50%, due to the poor condition of the old iron mains.

There is substantial debate on the economic level of leakage – that is, at what point is the value of the water saved by leakage repair work less than the cost of doing the work? Not least of the uncertainties in this debate is the effect of mains replacement on leakage level. So by the wholesale replacement of the Cheadle system, we established one point on the cost curve – we were able to show what it costs to take leakage down to the lowest conceivable level. From that point onwards, we can monitor the performance of the system over time and assess the costs of sustaining this very low leakage level.

MEASURING WATER USE REQUIRED METERS

To be clear in our assessment of the low level of leakage achieved by renewing the distribution system, we had some work to do on measuring customer use of water. Leakage is measured by taking the ‘night-line’ – that is, the flow into the distribution system at the time of lowest customer demand for water. But even at 2 a.m. there is still some customer use of water. To refine the leakage estimate, we needed to be able to say what customer use in the night-line really was. And that required the metering of all the properties in Cheadle.

Like the rest of the UK, Cheadle was largely unmetered. Households paid for water services on a charge related to the value of their property. To complete our information recovery, we needed to meter all the connections to the distribution system – but for our leakage analysis this was not quite enough.

Because we needed to be able to correct the night-line for customer use, we needed to take readings of customer meters at the same time as we were reading the distribution input meters. The challenge was to find a way of matching the timing of the meter readings. We decided that this had to be done using automatic meter reading, and that the method had to be fixed network rather than mobile, because of the need for simultaneous reading.

It has taken some 18 months to reach the stage where we have virtually completed the mains and services work and the metering work. The analysis of the data is underway, and we will be able to report later this year on the results.