Emfuleni, South Africa
The Alliance to Save Energy facilitated a performance contract for the implementation of a water efficiency system known as advanced pressure management on the bulk water supply pipeline into the Sebokeng/Evaton residential area. This area was characterized by excessive water wastage due to leakage. Because of the consumption of large amounts of electricity to pump water to where it is needed, the water saved as a result of implementing this project translates into savings in electricity, which also implies savings in the use of fossil fuels and especially low-grade coal to generate the electricity. This in turn translates into substantial reductions in CO2 emissions.
What is it?
Metsi-a-Lekoa, (the Water and Sanitation unit of Emfuleni Municipality), entered into a partnership with the Alliance to Save Energy to address the problems of water inefficiency that plagued both Sebokeng and Evaton, two residential areas of the municipality.
How does it work?
The Municipality of Emfuleni lies within the Province of Gauteng. Rand Water supplies bulk water from the Vaal Dam to the entire Province.
Because Metsi-a-Lekoa owed Rand Water a large sum of money, Rand Water conducted studies on why Emfuleni was losing such vast amounts of water.
Rand Water installed a data logger on the bulk supply line to Sebokeng and Evaton residential areas, which continuously measures and records the flow of water into the area under review.
The data logger indicated that the Minimum Night Flow (or the MNF, the best indicator of the level of water leakage and wastage for a particular area) for Sebokeng and Evaton was around 2,800 m3/hour, enough water to fill two Olympic sized swimming pools every hour.
80% of all water flowing into Sebokeng and Evaton was being lost mainly as a result of leaking plumbing fixtures on private properties. Thus, Rand Water quickly realized there was a big opportunity to implement a water efficiency project.
The Alliance to Save Energy (ASE) was made aware of this potential project and partnered with Metsi-a-Lekoa to facilitate the conceptualization, planning and implementation of an appropriate intervention measure.
ASE concluded that the best technical solution was advanced pressure management. By reducing pressure in the network, the amount of water that leaks through small undetected holes is also reduced.
Advanced pressure management consists of time and flow related pressure control valves housed in a single large above-and-below ground chamber together with other appurtenant plant and equipment.
In this instance, the equipment is comprised of five horizontal pressure control valves in parallel to the two co-located and parallel bulk water supply pipelines supplying the greater Sebokeng/Evaton area with water.
A pressure control valve is essentially a modulating (continuously opening and closing) valve that throttles the supply (flow) of water passing through it according to a desired (set) downstream pressure in the water network.
The downstream pressure (via the control valve) can be controlled via a time related electronic controller allowing the water pressure to be varied according to time of use over any 24 hour period. The electronic controller has up to ten settings per hour, allowing for water pressures in the network to be reduced especially at nighttimes when real water use in residential areas is very low (or when no one is using water).
ASE facilitated the signing of a performance contract between the municipality and WRP Consulting Engineers for the installation of the chamber and equipment. This contracting mechanism was deemed to be the best approach in light of the municipality’s limited ability to access capital and its lack of technical capacity, to implement, operate and maintain the required infrastructure.
A performance contract is a type of BOOT (Build-Own-Operate-Transfer) contract, with remuneration paid to the contractor through the resulting savings in water purchases from the bulk supplier of water to the municipality. The contract period in this instance is five years.
- Metsi-a-Lekoa and the Alliance to Save Energy are investigating the potential for further pressure management by dividing the water network area in smaller supply zones so that each one of these areas has its own advanced pressure management system.
- Active leakage control is also being considered, involving the detection of network leaks using sophisticated underground pipe leak detection equipment.
- Advanced pressure management works best in specific locations: places with high water wastage, high water pressure etc.
- The effectiveness of advanced pressure management is also dependent on the topography of the potential implementation area, working best in locations where bulk water is supplied from a high point to a low point.
- The application of advanced pressure management is much more complex where multiple supply points supply water into a large area. The fewer the supply points, the better (in this case there are only 2 supply points).
- In certain instances more localized (secondary) pressure control stations can also be installed downstream to a large control station where pressures in the network are still high due to undulating topography, but only where it is possible to ring-fence supply into smaller localized and discreet supply zones.