Due to the seriousness of the water shortage crisis over the past decades, the need to manage water usage has become increasingly important. NRW is water that has been produced and is “lost” before it reaches the customer. Losses can be real losses through leaks, sometimes also referred to as physical losses or apparent losses, for example, through theft or metering inaccuracies. A rough estimate says if the water losses in the developing countries be halved, the saved water would have been enough to supply around 90 million people.
Besides unauthorized consumption, water losses increase for :
- Leakage on transmission and/or distribution mains
- Leakage and overflows at utilities storage tanks
- Leakage on service connections up to point of customer metering
Among the NRW management strategies, water pressure management is the most popular towards the goals of effective and efficient water use. In an effort to improve the level of services provided to consumers, minimise its operating expenses and reduce water leakage and pipes’ bursts, water utilities reply on water pressure management.
Pressure management in urban water distribution networks is one of the options that can significantly reduce water loss. The pressure reducing valve (PRV) and the variable speed pump (VSP) are two devices that are most used in water distribution system (WDS) pressure management.
Due to increasing water demand in urban communities as well as reducing water resources, water loss management is one of the major challenges faced these days. Reports indicate that about 30%, or even more, of the total water entering the distribution network is wasted. There are many factors that contribute in leakage quantity in water distribution system (WDS), such as the water pressure, the pipe age, the quality of valves and fittings, the characteristics of the soil around the pipe, etc. Due to the direct relationship between pressure and leakage, pressure management is one of the effective methods to reduce leakage in WDSs.
The WDS is designed to deliver adequate water to consumers with the minimum acceptable pressure throughout the operation time, especially during the peak hours of peak days. Apart from that, during other operational period ‘when water demand is lower’, the network’s nodal pressure is more than the minimum acceptable pressure. This causes an increase in the background leakage, the pipe failure, and also energy losses (in order to create surplus pressure on the WDS). Therefore, pressure management of WDSs can play an important role in decreasing the water and energy losses, which has an effect on the sustainability of consumption and the protection of the environment.
The pressure reducing valve (PRV) and variable speed pump (VSP) are most used for WDS pressure management. PRVs, regardless of changing the inlet pressure or flow rate, can reduce inlet pressure to a steady lower set pressure. PRVs can be controlled with different approaches such as hydraulic or electronic controllers. PRVs with electronic controller can be used perfectly in supervisory control and data acquisition (SCADA) systems according to the momentary operation conditions. VSPs are pumps with variable speed drive (VSD). The VSD regulates the rotational speed of the pump’s electric motor by changing the frequency of the input power. Changing the speed of the electric motor can change the hydraulic performance of the pump, such as power consumption, outlet flow, and pressure etc.
Studies are on to find the relationship between network pressures and leakage losses and evaluate the effect of pressure control on water network leakage. Some mention about a linear theory method to find the optimal control valve settings to minimize the nodal excess pressure and also water leakage. The set point of the control valve need to be adjusted so that the pressure at the critical point (junction with the highest elevation or at the far end of the water network) remains within the allowable range. In a bid to effective pressure management, the minimum night flow (MNF) has been reduced by about 25% with nodal pressure reduction by controlling the outlet pressure of PRV.
Water loss through leaking pipes, have been a major threat to water utilities around the world. It is a general agreement that reducing pressure will reduce the leakage flow rate as well as the possibility of pipe burst. Frequent variations in pressure, are associated with higher frequency of new leaks. There is no doubt that pressure management is a fundamental tool in any leakage management strategy. Several pressure management strategies are available for leakage reduction in water distribution systems.