The City is using its recently approved mid-term adjustment budget of R54,2 million to replace pipes in Cape Town’s water network - in the first six months of the current financial year, it has already replaced some 21 km of pipes.

Water pipes are replaced when they have burst, largely because of ground movement, particularly where they have been laid in clay and cohesive soils. They may also burst because of inadequate compaction, or where certain types of trees are incorrectly planted over or are too close to water mains, in which case the root system dislodges the pipe as it grows.

The City’s 11 500 km pipe network comprises rigid materials such as cast iron and coated steel. In the more recent past, internally bitumen coated fibre cement pipes were used and nowadays the most common material for use in suburban streets is UPVC, which is able to withstand small movements without fracturing or bursting.

Pipes can also burst because of high internal water pressures which may burst them at a weak point. As water is normally gravity fed from the service reservoirs on the hills surrounding the city, the water pressure in the pipe network rises substantially (sometime to more than twice the daytime working pressure) once the majority of people have stopped using water, particularly at night.

To overcome this, some years ago the City began installing major pressure reducing valves that work in whole suburbs to adjust the water pressure as it rises. The first of these, the largest in the world at the time, was installed almost 10 years ago in Khayelitsha and another major scheme was installed in Mitchells Plain in 2008. Several other smaller scale pressure management projects are currently underway in Lwandle, Delft, Fisantekraal and Gugulethu. Commissioning of the Atlantis project will take place shortly.

”Pressure reduction devices will continue to be installed throughout the city where these projects show beneficial results. A start needed to be made and this has initially been focused in those areas where water losses have been the highest and where we can best put into practice our Water Conservation and Water Demand Management Strategy,” says Clive Justus, Mayoral Committee Member for Utility Services.

He notes that these pressure management devices not only reduce the incidence of pipe bursts and save the City’s valuable water, but also reduce leaks and bursts in residents’ homes. The Khayelitsha pressure management scheme is saving an estimated one million litres of water an hour which would have otherwise gone down the drain through leaks and bursts.

The City’s water reticulation performance is measured against international benchmarks and reported monthly at the Utilities Portfolio Committee meeting. Pipe replacement initiatives recently undertaken have improved the burst incident performance from 60 bursts/100 km/year down to 50 bursts/100 km/year.

Whilst a database for bursts is maintained, the planned replacement programme is at present informed by the reactive burst incident record, and is also governed by the available remaining capital budget allocation. A metro-wide, proactive (planned) programme for pipe replacement is not yet available; however the proposed Integrated Asset Management Plan will address this shortcoming. “Pipes which have reached the end of their useful life are however, being replaced,” says Justus.

The majority of pipes requiring replacement are 100 mm diameter, and these are replaced at an average cost in excess of R1000/m. Approximately 6 km was replaced in 2006 and this figure has grown to 46 km in 2008/09 financial year. Some 21 km of pipe has already been replaced in this financial year.

Justus says that budget reductions in the second half of the year caused by the general economic downturn may however prevent similar replacement rates as last year.

Residents can report burst water pipes to the Technical Operations Centre on 0860 103 054.