“The amount of losses a utility should recover depends on the individual utility”
Water loss management can lead to water savings and net economic benefits, but is there an optimal level of water loss? Researchers use engineering and economic principles to take account of the heterogeneity of water losses to arrive at the most economically efficient level of water loss reduction.
As water utilities grapple with scarcity and uncertainty of water supplies, leak management offers an opportunity for water savings. While some leaks will be evident and accessible, others will be costly to find and repair. Dr Amanda Rupiper has been carrying out research related to wateruse efficiency and sustainability at the Center for Water-Energy Efficiency at UC Davis. We interview her about her research on water loss management and the implications for water suppliers as well as for policy and regulation.
Can you tell us briefly about your career path and your current research focus at the University of California, Davis?
I started my career out as an Environmental Scientist working for the California Department of Public Health as a regulator in the Drinking Water Program and then moved into a Chemist position in the State Drinking Water Laboratory. In these roles, I was able to visit many small water systems throughout Northern California and work with several Environmental Engineers. This work inspired me to increase my involvement in California water management issues and go back to school to get my Engineering degree – which brought me to the University of California, Davis (UC Davis).
Concerning water losses, what is best for one utility may not be best for another and a one-size-fits-all approach can be detrimental
I have been very fortunate while pursuing my Ph.D. to work with the Center for Water-Energy Efficiency at UC Davis and participate in a variety of research from decentralized water reuse to water loss management. Since completing my degree, I have stayed on with the Center for Water-Energy Efficiency as a post-doctoral researcher. I am currently working on a few projects including one related to energy load-shifting in the water sector. This work specifically examines the potential of water distribution systems to use their existing water storage to shut off their distribution pumps when energy costs are high and energy grids are strained and increasing pumping during low cost or low emissions periods to increase the integration of renewable resources with the Californian energy grid. Other projects I am actively working on include quantifying the impact of advanced metering infrastructure on water consumption and end-user water leaks and an equity assessment of various water rate structures in North and South America. In the fall, I plan to continue working on research related to efficient water management, water loss, and related topics in a new role as faculty at the University of California, Riverside.
Why is it important to assess water loss at the utility level?
Utilities are complex and unique - what is best for one utility may not be best for another and a one-size-fits-all approach can be detrimental for many utilities. The easiest way for me to explain this is with an example of two utilities of identical size, identical costs to produce a volume of water, and identical levels of leakage, 15% of their annual water demand. The only difference between these utilities is the rate at which new leaks develop within their system, a metric commonly referred to as rate of rise. Utility 1 has a newer distribution system where leaks develop somewhat slowly. Utility 2 has an older distribution system where leaks develop five times faster than Utility 1.
For some utilities the cost of achieving a uniform regulation exceeded the benefits of saved water, meaning they lost money
Assume a regulation did not take into account utility-specific data (e.g., rate of rise) and instead required each utility to bring their water losses down to 10% of their water demand. In order for Utility 1 to accomplish this, they may only have to search for and repair leaks every five years. In order for Utility 2 to accomplish this, they may need to perform leak detection surveys and repairs each year at a significant cost. This regulation will result in Utility 2 paying five times more than Utility 1 to achieve identical benefits (i.e., the value of water saved).
This example only considers one utility-specific factor, but you can imagine that other factors could have similar impacts. What we found when looking at models that did not assess water losses at an individual utility level, was that for some utilities the cost of achieving a uniform regulation exceeded the benefits of saved water, meaning they lost money. In addition, these approaches disproportionally affected utilities, causing some to pay as much as ten times what other utilities were paying per volume of water saved.
We tried to incorporate as many utility-specific characteristics as possible, including five values pulled from annual water audits
You found cost-effective leak management depends on utility-specific characteristics. Which characteristics do you take into account in your model?
We tried to incorporate as many utility-specific characteristics as possible. In our study, we applied the model to almost 900 utilities, which meant we were somewhat limited in which utility specific values we had available to us. We used five different utility-specific values pulled from annual water audits; length of mains, number of service connections, average pressure, current annual real losses, and variable production costs. Everything else in our study was based on defaults found in literature or estimated using data from several water suppliers that provided us with detailed data. For our analysis, we felt comfortable using defaults because while the actual values for an individual utility are likely more or less than that default, on average we would be representing utilities as a whole. If an individual utility were to use our model to estimate what is the most cost-effective level of water losses for them, they should replace as many of these defaults as possible with values specific to their system. We built the model to use utility specific data for many parameters including: leak detection survey costs, leak detection method accuracy, infrastructure condition factors, rates of rise, pressures in individual zones of the distribution system, water cost growth rates, and others.
How does the model you developed arrive at an economically efficient level of water losses?
Economic efficiency relates to the level of water loss reduction that maximizes the difference between benefits and costs to a supplier
Economic efficiency relates to the level of water loss reduction that maximizes the difference between benefits and costs to a water supplier. In other words, this is the level of losses where the incremental (a.k.a. marginal) cost of an action like leak detection and repair is equal to the incremental benefit, which in this case is water savings. To find the level of water loss reduction where this occurred we used utility specific data to create a cost curve as a function of leak reduction activities. Assuming that every unit of water saved is equal to the last (i.e., constant marginal benefits), we were able to maximize the net benefits (total benefits – total costs) by minimizing the total cost equation.
In practice, we did this for two water loss management activities, leak detection and repair and pressure management. Minimizing the cost curves for each of these activities allowed us to estimate how often a utility should perform leak detection and in what zones of the distribution system to reduce pressure. Once we identified these activities, we could translate them into new water loss levels.
How does your approach to water loss management differ from existing engineering standards of practice?
Much of what went into our approach is not new, we took advantage of principles that are fundamental to engineering and economics and brought them together. I think the most important thing about our work that has not been done in this way before was that it took a big picture approach. By examining hundreds of utilities from several states, we were able to see the implications of policy and modeling choices on individual utilities as well as overall and the benefits of managing water losses efficiently.
Can the model be adapted to the situation in different countries?
Yes, definitely. Since we designed the model to use as much utility specific data as possible, it is very adaptable to different situations and conditions. The one big assumption that the model does make is that water distribution pipes are constantly pressurized. So long as this is true for a water system using the model, everything else can be tailored using data specific to the water provider.
Uniform approaches to water loss regulations will result in some utilities doing too much, some doing too little, and some losing money
One important thing to note is that we populated the model with defaults in the place of missing data. We selected defaults to represent the US states whose data we used in our study. If this model is adapted for a different country it may be worthwhile to consider which defaults should be changed.
How can your findings inform water loss policy and the development of regulations?
There are many ways to approach water loss regulations and since creating a unique water loss standard for each utility can be onerous and require significant amounts of data and knowledge, which may or may not be available or reliable, it is tempting to apply a blanket regulation. For example, all utilities should get their water losses down to 10% of their annually distributed water, should reduce their current levels of losses by 25% or should perform leak detection surveys every two years. However, all three of these ‘uniform’ approaches will result in some utilities doing too much, some doing too little, all of them paying different normalized costs to achieve the standard, and some utilities losing money.
If nothing else, what our findings have shown us is that while there is a great opportunity to reduce water losses at a benefit to the water supplier, the amount of losses a utility should recover depends on the individual utility.
To what extent may novel technologies to detect leaks and monitor pressure in water systems influence water loss management?
New and emerging technologies are increasing the accuracy of leak detection, continuous leak monitoring is finding leaks earlier, improved data and metering accuracy is helping better understand and characterize real water losses, and improved pressure monitoring can help identify even small or short durations when pressure can be reduced to decrease leak flows. All of these technologies and advancements can help reduce water losses in a system, but they come at a cost. As the cost of installation of these new technologies comes down, the economically efficient level of water losses will also decrease. This means that all else being equal, it will become more economically beneficial for a utility to save more water if the actions or technologies employed to save water are either cheaper or more efficient.
The saying that change is the only constant in life applies here. As technologies change and improve, as utilities grow and update their systems, as the cost of water fluctuates, so too will the economically efficient level of water losses. Leaks that make sense today might not make sense tomorrow and should be regularly reassessed using sound economic and engineering principles.