WaterSubject

The effect of employing demand and pressure management techniques on the cost of water reticulation systems is analysed in this paper. The analysis is based on the cost of supplying a cluster of 4000 households serving a range of hourly demands using pipes of various pressure classes. Demand management reduces costs by 25–45% and pressure management increases savings by a further 20–55%. For demands below 50 l per household per hour there is a cost shift from reticulation infrastructure, to properties, to cover the costs of water storage and fire sprinkler systems. The analysis highlighted the hidden cost within water supply infrastructure to provide fire protection based on street hydrants.In Australian cities, as in most cities of the world with high living standards, design of water supply networks for peak flow has become the accepted norm. This has led to an overcapacity in the distribution system for most of the year and, on a diurnal basis, for most of the day. However, today water distribution systems are gradually coming under increasing strain as population growth exerts more pressure on existing water resources, as discussed. Urban consolidation and fringe area developments increase demand on distribution systems––both, however, are population growth (demand) effects––hence the widespread move towards the introduction of demand management measures, and the use of alternative sources, e.g. rainwater storage tanks. Alternative supply methods that encourage more sustainable consumption of water may need to be considered in the future. Many studies in Australia and overseas have researched and analysed the options for the future. Along with conservation strategies, solutions are required to reduce the cost of infrastructure. Because the pipeline network in the water supply system conservatively accounts for around 75% of the total infrastructure costs associated with water collection, treatment and distribution, this is the area where major savings in infrastructure costs can occur with advances in technology or operational methods. Only small savings in infrastructure costs can be made in the area of water treatment and storage and, in fact, with increasing concerns over water quality, it is expected that the costs of water treatment infrastructure will increase in the future rather than decrease, as technologies such as membrane filtration are required. The responsibility of meeting these challenges lies with the water authorities. However, like many other organisations, water authorities, whether in the public domain or operated as commercial enterprises, are affected by two of the major forces in the world today––fiscal restraint and environmental awareness. On a basic level, one usually does not complement the other because environmental solutions cost money. With creative solutions, however, many sectors of the economy are finding that in fact the two can go hand in hand. Water authorities are no exception; they are expected to meet these challenges while delivering potable quality water to consumers at a reasonable price, maintaining and upgrading the infrastructure to ensure security of supply, and also protecting stored waters.

This report is based on costing of pipeline systems in a conventional water service and in several conceptual scenarios with normal and reduced demand levels. The peak instant residential demand on the reticulation system in Australia is about 220 l per household per hour (l/hh/hr). However, for some locations, this demand can be much higher, especially during summer peaks. If the load is spread more evenly across the full 24 h it can be reduced significantly. Consequently, demands of between 8 and 415 l/hh/hr are considered in this analysis to cover the expected extremes. Regulation of supply pressure is also considered as this has a significant impact on the cost of supply pipelines. Most networks in Australia are designed for 1600 kPa pressure (PN16 pipe). Traditionally water authorities have tried to supply their customers with a minimum peak demand pressure of 150 kPa. By regulating the supply at the local distribution level to 250 kPa maximum, while maintaining the 150 kPa minimum at peak demand, it is possible to design a reticulation network with lower class pipe in areas with flat terrain, thus limiting the total pressure in the pipe. With the current widespread use of plastic pipe, the potential exists for significant savings. Therefore the paper also analyses the cost implications of using PN4, PN6.3, PN8, PN12.5 and PN16 pipes in the reticulation system.Analyses of a conventional reticulation water system and alternative scenarios based on reduced demand and pressure reduction, have shown that considerable savings can be achieved by water authorities or property developers in the cost of providing these services.

Regulation of the pressure supplied to households to deliver a minimum pressure of 150 kPa at peak demand, allows the use of lower pressure class pipes. This offers water authorities (property developers) savings of up to 58% in the reticulation network to supply a cluster of 4000 properties when PN4 pipes are used.

The use of demand-reduction techniques, whilst allowing water authorities considerable additional savings in the reticulation network, shifts the majority of these savings as an extra cost across to the property owner, by requiring the property owner to provide for on-property water storage and in-house fire-suppression systems.

The analysis has highlighted the cost of providing infrastructure for public firefighting services and indicated that alternatives are available, however, these are currently considered controversial and are in need of further research.