An effective way to reduce non-revenue water, improve energy efficiency and lower operation and maintenance costs.
Pressure management has proven to be an effective tool for reducing the leakage part of non-revenue water (NRW), improving energy efficiency and reducing operation and maintenance costs. This article looks at the benefits of tackling these issues using pressure management, especially as the predicative models for burst frequency are now more precise (see Fig.1). Extended asset life, based on latest research results, is expected to be the largest benefit with pressure management.
Fig. 1: Multiple benefits of pressure management.
A major challenge facing many municipalities is how to deal with high levels of NRW. Although not all NRW is leakage, inefficient management of distribution system pressures is known to cause substantial excess leakage and bursts and other adverse consequences such as reduced infrastructure life.
We discuss here three main areas of benefits related to pressure management implementation, namely non-revenue water, energy efficiency and operation and maintenance costs.
Leakage component of non-revenue water
NRW is the difference between the amount of water put into the distribution system and the amount of water billed to the end-user. High levels of NRW affect the financial viability of water utilities through lost revenues and increased operational cost.
The total cost to water utilities caused by NRW worldwide is estimated conservatively at $14-billion per year, with a third of it occurring in the developing world, according to the Energy and Water Department of the World Bank Group.
NRW includes unbilled authorised usage (fire fighting, flushing, and others) and apparent losses (customer metering under-registration and unauthorised usage), both of which represent water used but not paid for, and are only influenced marginally by pressure management. The remaining component of NRW – leakage and overflows from water utility transmission and distribution systems – represents a wasted resource that can often be reduced significantly by means of pressure management.
The leakage component of NRW varies from 95% down to 50%, depending on apparent loss levels due to theft and customer meter under-registration, which is greatest in systems where customers have storage tanks.
On average, flow rates of individual leaks vary linearly with average zone pressure. By reducing both the frequency and flow rates of leaks, pressure management can reduce the amount of money spent on producing and/or purchasing water, and on the consumption of energy required to pump and treat water for distribution. Intelligent pumping solutions and advanced pressure reducing valves can make a significant difference, but care is needed in identifying those parts of a distribution system that will benefit most from pressure management, and also the particular form of pressure management that is most appropriate.
Energy efficiency
Water supply systems are massive users of energy along the multiple stages of water production and supply chain: water abstraction, treatment processes and pumping stations within the supply system.
For most water companies, energy is the highest operating cost item after manpower. According to the Environmental Protection Agency (EPA), water and wastewater systems spend about $4-billion a year to pump, deliver, collect, treat and clean water. The EPA also predicts that energy usage at water and wastewater utilities will grow by more than 20% in the next 15 years. About 90% of the energy used in water distribution is used by pumping systems.
Energy costs can represent, in water systems of large dimension, 80 to 90% of the total life cycle costs of pumping stations. Energy efficiency offers an opportunity to achieve cost reduction in the operation of water pumping systems, especially with regard to the expected rise of energy prices.
It is therefore clear that developing and implementing solutions that can reduce the use and the cost of energy is the right approach for efficient management of water distribution systems.
Historically and even now, the control functions in most water management systems are targeted to cope with operational constraints and demands without considering the drawbacks from too high pressure settings in the network. This is, however, due mainly to the lack of appropriate technologies that can address the cost function and lack of adequate knowledge about the consequences and related costs associated with excess pressure in the system.
Fig. 2: Characteristic relationship between AZPmax and burst
frequency for individual zones (reproduced with the permission of WLRand Ltd)
Operation, maintenance costs
Europe alone has 3,5-million km of water distribution networks. Water utilities face a number of challenges related to these distribution networks. In the next 10 to 30 years, large parts of water distribution networks will need to be rehabilitated. Based on experiences of major European water utilities and taking into account the state and performance of distribution networks, it is possible to estimate that €20-billion per year will be needed in Europe to upgrade distribution networks.
Prioritisation and optimisation of these investments is needed urgently.
Strategic prioritisation, allocation of capital expenditures
Employing dynamic pressure management tools can result in 10 to 15% savings on capital expenditures by directing investment strategically. Based on the estimate of the investments needed in Europe, such dynamic pressure management tools can save up to $2-billion annually.
Relationship between pressure, burst frequency
Until quite recently, calculations for the economic case for pressure management were traditionally based only on the predicted savings from the reduction of flow rates of existing leaks. Thornton and Lambert demonstrated that reduction of excess pressure in zones with high burst frequencies could have a substantial influence on reducing bursts, and that separate predictions were needed for mains and for services. Over 110 case studies in eleven countries showed an average percentage reduction in burst frequency of 1,4 times the percentage reduction in average pressure for mains and services, with corresponding significant reductions in overall repair costs.
The latest established relations between pressure and burst frequency
(see Figs. 2 and 3) are now being used to make practical predictions of changes in burst frequency in an increasingly wide variety of countries and situations. However, the largest financial benefits are likely to be deferred pipe renewals and extension of asset life, as explained here.
Fig. 3: Mains repair frequencies pre and post-pressure management Durban CBD showing more than 50% drop in burst frequency and therefore similar savings in maintenance costs (reproduced with the permission of Ethekwini Municipality).
Deferred renewals, strategic prioritisation, allocation of expenditures
Significant reductions in burst frequencies on mains and services following large-scale pressure management are beginning to have an influence on the numbers and choices of pipes which are renewed each year. Water utilities with policies to replace their mains and services based on defined customer service criteria such as “X bursts in Y km in Z years” are now retaining some mains and services that would otherwise have been replaced. Early indications from Australia are that financial savings arising from this can be several times the annual savings in burst repair costs.
A careful analysis is needed to identify those parts of a distribution system that will benefit most from pressure management and to assess the specific benefits.
How pressure management may affect usage
Some water utilities are concerned with potential losses in revenue after pressure reduction. When system pressure changes, some of the components of metered consumption may be affected and pressure management may result in a change in the income received by the water utility from metered customers.
Based on prediction models recently developed in Australia, probable changes in consumption can be predicted, based on assumed change in average system pressure, estimated percentage of annual residential consumption outside the property, presence of private storage tanks, and/or private booster pumps.
However, whether reductions in consumption from pressure management are considered to be a benefit or a cost, the volumes usually seem to be relatively small in relation to the reduction of leak flow rates, burst frequency and extension of infrastructure life. Because consumption is charged at retail price, the financial implications should be calculated so that the implications on the revenue of the water utility are predicted and identified.
Benefits for resource management, customers and communities
Additional benefits from pressure management include:
Water resource management
Pressure management permits the water utility to vary pressure over both the seasonal and daily cycles of demand, providing the minimum required standard of service for pressure at customers’ premises.
Pressures can be reduced further during drought periods when water supply restrictions apply. The alternative to imposing intermittent supply is most likely to increase burst frequency and damage the distribution system permanently.
Countries such as Italy now require water utilities to report their average pressure along with their water balance calculations and NRW performance indicators, and this should be regarded as best practice for others to follow.
Improved customer service
Regulators are increasingly focused on customer service issues by introducing key performance indicators for interruption, continuity of supply, minimum pressure, and others. Pressure management schemes are normally designed to comply with such criteria in a cost-effective manner.
Minimised community disruptions
Water mains bursts and other major system failures lead to disruptions in daily life – thousands of hours of lost productivity in addition to the cost of repair. Continuous pressure and flow monitoring, which is a normal part of pressure management, reduce the number, severity and duration of these disruptions.
Minimised damages to customers’ plumbing
National plumbing standards specify and reduce the maximum permitted pressure that customers receive to avoid reducing the life of customers’ appliances (taps and fittings) and for reducing excessive noise.
Reduced liability costs
Many water utilities suffer catastrophic water pipe failures every year. In addition to losing precious water and costing millions of dollars to repair, these failures also cause interruption to the everyday life of the end-user and damage to the water utility.
Many variables can contribute to a catastrophic failure but excess pressure at night or pressure transients are often found to be the straw that breaks the camel’s back. Pressure monitoring and management can assist in reducing the frequency and the effect of these failures, so saving money for the water utility and improving customer satisfaction.
Opportunities and solutions
Pressure management represents one of the biggest opportunities to improve water utility performance. When considering pressure management, the first objective is to identify the presence of pressure transients and to minimise their adverse effects. The second objective is to move from intermittent supply to continuous supply (also known as “24/7 supply”) at a lower pressure, if necessary. Reduction of bursts through the control of pressure transients and slow refilling of systems is one key aspect of this policy. The other key aspect is that lower continuous pressure reduces leak flow rates when the system is pressurised.
Reducing average and maximum excess pressure by only 10% produces a reduction in leakage, reduction in pipe bursts, deferred renewal and extension of residual asset life, as well as energy savings.
Table 1: Three different control approaches evaluated against their effect on water leakage,
energy efficiency, and operation and maintenance costs.
Problems facing water utilities and benefits with different modes of operation
Intermittent supply: (Not “24/7” operation).
Continuous supply: (excess pressure).
Optimal pressure management: (demand driven distribution).
NRW – high leakage component
Leakage flow rates reduction due to limited time of pressurisation. Very high burst frequencies on mains and services. Big risks of contamination when the pipes are not pressurised.
High burst frequencies due to higher than required maximum pressures for much of the time. High leak flow rates due to higher than required average pressures.
10% reduction of average pressure produces 10% to 20 % reduction in annual leakage (depends on pipe materials and type of leaks).
Energy efficiency
High energy costs for pumping as higher flow rates are imposed to move the same volume.
Excess energy costs due to excess pressurisation from pumping.
10% reduction of excess average pressure produces around 10% decrease in energy costs from pumping.
Operation and maintenance
High manpower costs for valving operations. High repair costs.
High repair costs, high liability costs.
10% reduction of average pressure decreases economic intervention costs of active leakage control by 10%.
Active leakage control is difficult due to insufficient pressure.
High active leakage control costs due to higher rate of rise of unreported leaks.
10% reduction of average pressure decreases economic intervention costs of active leakage control by 10%.
Short asset life time due to poor operation and pressure transients.
Short asset life time due to excess pressure.
Deferred renewals, residual asset life extension. This benefit can be very substantial; prediction methodology for pressure reduction being developed.
Methods and concepts now exist to calculate payback periods and financial benefits for different pressure management options in different parts of the water utility’s distribution system.
Pressure management by means of smart pumping technologies and pressure-reducing valves can be leveraged to help address these water challenges. Awareness of the benefits of pressure management in distribution systems in combination with practical methods to make predictions of these benefits and the capability to make a sound financial case for such investment make that possible today. Advancements in technology that deliver enhanced data allow the adjustment, control and monitoring of pressure, and then quantifying and certifying the results achieved. It is important to understand the business case for using proper pressure management technologies as an alternative to investing heavily in capital expenditures, and to assess the potential annual savings related to pressure management implementation.
The way forward
Pressure management will begin to take hold when the potential value for water utilities becomes clear and capturing that value is made easier. This shared understanding, while necessary, is not sufficient to drive widespread adoption of pressure management. Only with a concerted effort from all major stakeholders can the water industry be redefined and overcome the challenges posed by water scarcity and water quality.
Provided water players join forces, the following key challenges for implementing pressure management are not insurmountable:
Lack of awareness of achievable benefits: Most water utilities are still not fully aware of the benefits achievable with pressure management implementation. Design of new or extended systems to operate at low steady pressures would be very beneficial.
Lack of funding: Possible solutions to lower the barrier to entry include risk-sharing contracts to lower upfront investment required and third-party suppliers who implement technical solutions and analyse the data.
Lack of political and regulatory support: Regulatory support, as well as incentives, would be critical for kick-starting pressure management, beginning in water scarce areas where the need for water efficiency and conservation is greatest.
Resolving issues with pressure management
The network pressures must be measured and the pumping station controlled according to these measurements to obtain the best possible pressure management. However, online communication between the network pressure sensors and the pumping station is expensive and hard to set into operation. This is solved with the demand-driven distribution solution from Grundfos (see Fig. 4).
Demand-driven distribution measures the pressure in the network using a number of battery-driven data loggers that transmit the measured and logged values to the demand-driven distribution controller via the GSM network, using just one SMS text message per sensor a day. The measured data is then used in a smart adaptive control approach that controls the pumping station, keeping the pressure in the network at the desired value without analysis and re-configuration of the system.
Pressure transients are one of the main reasons why cracks are created in piping. To avoid the pumping station creating such transients, pressure ramping is standard in the demand-driven distribution controller.
Fig. 4: The demand-driven distribution controller connected to network
pressure sensors via the GSM network allows control of the pumps in
accordance with the logger data via a smart adaptive control algorithm.
Progress on pressure management
Pressure management is developing further and includes research into pressure management benefits as well as new technologies for pressure management implementation. Some of the areas being looked at include:
Intelligent technologies to optimise distribution, pump pressure and pressure-reducing valves’ pressure.
Pressure-bursts relationships and the influence of pipe materials.
Validation of scheme results and implications of extended asset life.
Guidelines for transient analysis in water transmission and distribution systems.
Pressure management in very low-pressure zones.
Acknowledgements
This article was prepared by Marco Fantozzi, Studio Marco Fantozzi, Italy, with contributions from Allan Lambert, Water Loss Research and Analysis, UK; Carsten Skovmose Kallesøe, Abdul-Sattar Hassan, Danny Stærk, Allan Nielsen, Jørgen Bach and Morten Riis, Grundfos Holding, Denmark.
The authors wish to acknowledge the assistance of the Water Services Association of Australia; Ethekwini Municipality, South Africa; APA-NOVA Bucharest, Romania; Essbio, Chile; Frederikshavn Forsyning, Denmark and other water utilities who permitted their data and experiences to be cited in this article. Members of the Water Loss Specialist Group are also thanked for their contributions to the ongoing research into pressure management benefits.
References
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Contact Linda Gradidge, Grundfos, Tel 083 629-7149, lgradidge@grundfos.com
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