DAY ZERO IN CAPE TOWN, SOUTH AFRICA
The world’s first major city is about to run out of water. The Theewaterskloof Dam reservoir—which normally supplies water to a city of four million people—is almost empty of water and is being filled with sand dunes. Since 2014, the drought has also affected the millions of inhabitants of Western Cape Province who depend on these water sources. The South African government has begun limiting water use. The city’s water system managers have projected a date when the city runs out of water, a date given the name “Day Zero.” At that point the city will have to install 200 centralized water rationing stations guarded by local police and security forces. Hospitals and other essential services will be exempt, but most residents will face severe restrictions on water consumption that could endanger basic health and sanitation. As the climate changes, Cape Town is not alone. From drought-stricken Syria to the fires of California, water scarcity is threatening the basic requirement for the existence of any city: a secure source of clean, potable water.
The response of the Cape Town government has been to ration the consumption of water by a cycle of ever-tightening restrictions. The residents of Cape Town have been told to limit their water use to only 23 gallons per day. By contrast, the average American uses up to 100 gallons of water per day. And now the city is preparing to reduce daily water usage once again to a mere 13 gallons per person, a rationing to be enforced by severe legal penalties and hefty fines. And this time, rationing is not limited to just city water consumed for personal use, it now will include private wells and irrigation systems. Despite these rationing programs, Cape Town’s populace is consuming 20% more water than is being allowed.
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Though the root cause of the water shortage is the unprecedented, extended drought, there are other factors making the situation far worse than it needs to be. The city’s water supply infrastructure is overburdened, antiquated, and in need of repairs and upgrades necessary to minimize further water losses from the water distribution system. “The current level of Non-Revenue Water estimated for the country as a whole is 36.8%” (Source: WRP Consulting Engineers (Pty) Ltd, The State of Non-Revenue Water in South Africa, Water Resource Commission, August 2012). So fully two-fifths of South Africa’s water supply is lost before it ever gets to the consumer. Eliminate these losses and even this severe drought becomes manageable.
What is left after these “non-revenue water losses” is not distributed evenly. The city’s population has exploded over the past few decades and extreme income inequality combined with inefficient planning policies have led to major distribution differences between urban regions and neighborhoods. Single-residence suburban communities consume 55% of available potable water. The informal settlements, with the bulk of the region’s population, use less than 5%.
Long-range plans include desalination plants and tapping deep underground aquifers. Though Cape Town is a coastal city and possesses significant groundwater resources, accessing these sources requires significant financial costs and energy use. But the city’s tax base and other sources of funding are as limited as their water supply. Current projects are underfunded and behind schedule. Aquifers are already being used by local farmers who depend on this water source for irrigation and supplying the city with food. South Africa’s non-revenue water losses are approximately equal to the average of such losses for the world as a whole. Cape Town, unfortunately, is not unique.
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WATER SYSTEM LOSSES
These water losses are usually referred to as “non-revenue water” (NRW), the water that escapes from the distribution system or is otherwise unaccounted for. NRW includes several different types of loss, not just actual physical leaks of water escaping the pipe distribution system. These other NRW losses include misread meters, meters that have been tampered with to give a lower reading, broken meters, poor bookkeeping back at the water system office, and actual physical theft. In addition to the loss of potential revenue from NRW, the presence of physical leaks can also allow impurities to enter the water supply, putting the health and safety of consumers at risk. Not all water that is not measured is considered NRW—some water use is authorized but not billed for. There is a classification for “unaccounted for” water such as water used for firefighting.
Water losses are measured by various metrics. NRW is measured over a fixed period of time, typically years for annual budgeting. It can be measured in terms of total losses per given time period (such as gallons per year), as a percent of the total water supply volume over a period of time, and water loss per length of pipe system (gallons per mile). Losses will vary with the age and conditions for each section of the distribution system, the type of piping used, the local pressure and elevation differences in the water system, availability of funding for maintenance and repair, etc.
The water distribution system where these losses occur is a complex network of pipes, valves, and appurtenances. A leak may occur at a crack in a pipeline or at any joint where these various fixtures meet. The water within the pipe is under considerable pressure from gravity and elevation differences and/or by applied pressure from water pumps. And while this pressure is unnecessary to move the water through the pipelines, it can greatly exacerbate water losses from even a tiny hole or crack.
Being mostly underground, flaws in water system pipes are not readily noticeable or even easy to locate. The main reason pipes fail and develop flaws is simple age and related deterioration from rust, biological clogging, corrosion, etc. These can act to weaken and thin the walls of the pipes over time until a sudden load, shift in adjacent soil, or expansion from temperature changes cause an actual breach in the wall or a separation at a joint.
Stress concentrations from these applied loads can occur at any of the potential weak points created where pipes join appurtenances (bends, valves, tees, wyes, or flanges). These connections are always weaker than the solid walls of the pipes themselves. The applied loads include equipment vibrations, pressure thrust, and water hammer created by the flow of water within the pipes themselves, exterior loads from soil overburden or the cavitation of soil under the pipe which removes its support from below, and the forces generated by temperature-induced expansion and contraction in the pipe or the freezing and thawing of water within the pipe.
Which types of pipes are more susceptible to water loss? Most modern water distribution systems are a mix of several different types of pipe, depending on their location branching off from the transmission pipe. Main aqueducts and water mains are made from large diameter reinforced concrete pipe segments. Branching off from these mains are the regional and neighborhood service pipelines constructed from several different types of materials such as cast iron, ductile iron pipe, stainless steel pipe, and polyvinyl chloride (PVC) pipes. Branching off from these service pipelines are the smaller diameter individual feeder lines usually made from Type K copper pipes or, in older systems, old-fashioned lead pipes.
Diameters vary as well, with larger mains and aqueducts measuring many feet in diameter. Service pipelines can vary from 6 inches to 16 inches, with 8 inches being the most common. Lastly, individual feeder pipes can vary from 0.5 inches in diameter for residential homes to 6 inches for commercial and industrial customers. The combination of material types and sizes determines a pipe’s overall strength and its vulnerability to failure and leakage, especially at the joints. Welded joints (such as those used with stainless steel pipes) completely seal off a pipe, effectively reducing leaks along a pipe segment. Older pipe systems with fitted joints, such as bell and spigot joints requiring a rubber gasket to complete the seal, will tend to be more vulnerable to leaks over time.
A desalination plant
The problem then becomes how to find and fix these leaks. Being buried underground makes leak determination and location inherently difficult. Pinpointing the sources of water loss, let alone determining the cause, is a major challenge. The first difficulty is the fact that not all NRW represents a physical loss. Some losses are just the result of cheating by consumers. However, with modern sensor and monitoring technology cheating and theft have become much more difficult to pull off and easier to detect. As such, this is now more of a problem in developing nations that lack the resources to install this technology. There, theft, misreporting, and illegal taps can still take up to 40% of total NRW losses.
And while theft can be easily detected and deterred, technology still has not advanced to the point where finding physical leaks is easy. So long as water pipes are buried underground, direct observation is impossible and indirect detection can be difficult and time-consuming. Often, only the most significant water loss occurrences, such as a water pipeline brake, are obvious and can have significant repair resources assigned to their correction.
The first step is determining if a leakage problem exists in the first place. This is accomplished by performing a water audit. Though often costly and always labor intensive, a water audit is a very cost-effective investment for a water utility. These audits can be either unvalidated (pencil and paper audits with error ranges as high as plus or minus 50%) or validated (utilizing specialized software tools, involving the sampling and testing of meters, review and elimination of billing errors, and the mapping of illegal taps by field surveys). An unvalidated audit is the initial stage screening process while the subsequent validated audits follow through and get to the root of the problem. To evaluate this data, an overall Infrastructure Leakage Index (ILI) has been developed. ILI has been defined as the ratio of the actual Current Annual Real Losses to the estimated theoretical Unavoidable Annual Real Losses (CARL/UARL). A perfectly managed water system would have an ILI of 1.0 (CARL = UARL). But for real-world water systems, ILI is always greater than 1.0.
Finding a leak is often a methodical and time-consuming process of bracketing its location. The first step is to take water pressure measurements at key nodes, connections, and branch lines. The measurements can create a pressure isobar contour map across the system (after taking into account pressure differences due to different elevations of the pipe inverts). Areas of lower pressure would tend to have leaks exposed to atmospheric pressure regimes. Further data is provided by meter readings that record flow rates and usage by each consumer. These too can be mapped and can show water losses between point A and point B based on these meter readings. However, it has been found that monitoring changes in water losses over time or benchmarking them between utilities is not an appropriate measurement since water loss quantities can vary considerably over time relative to total water consumption. A better way to measure water losses is in terms of absolute losses per connection per day. Though more time consuming and expensive, this approach yields greater accuracy of results.
Together these data sets can help a water utility zero in on the potential location of a significant leak. Once a potential location has been determined, acoustic readings can be performed along the length of the suspected pipeline to detect the telltale hiss or rush of escaping water. Once the potential site is isolated, exploratory excavation (preferably performed with a hydro or air excavator to minimize potential damage to the pipeline and any other adjacent buried utilities) can be performed. Once exposed, the leak can be repaired and its associated appurtenance replaced if necessary.
The effective management and minimization of NRW is based on four principles: active leakage control, pressure management, infrastructure management, and speed of repair. Active leak control is the process described above where leaks are isolated, located, and repaired. But this approach soon reaches a point of diminishing returns as the more obvious leaks are found and repaired and each new round of smaller leaks become harder and harder to locate. Pressure management involves the installation of add-on pressure reducing valves (PRVs) that reduce high-pressure locations in the system and minimized the potential for leakage. But the use of too many PRVs is costly and can affect necessary pressures and resultant flow rates within the system. Active infrastructure management can determine and predict which components will soon fail or be most prone to leaks. Again, this approach also faces a point of diminishing returns as the more obvious failed components are replaced. Quick reaction to leaks emphasizing speed of repair reduces the amount of leakage by limiting the time the pipeline is leaking. But this approach is labor intensive and most water utilities have limited manpower resources.
And while there is no perfect, one size fits all approach to leak management, the effort itself makes financial sense up to a point—a point defined by the system’s economic level of leakage (ELL). The International Water Association (IWA) has defined ELL as “the level of leakage where the marginal cost of active leakage control equals the marginal cost of the leaking water” and as the “economic level of real losses [that] occurs when the sum of the value of the water lost through real losses and the cost of activities undertaken to minimize real losses is at the minimum.” In other words, it is the point where money expended on leak management and improvements to the water supply system (such as additional metering, pressure controls, improved pipe materials, and telemetry applications) exceed the amount of revenue saved by preventing the leaks in the first place.
CONCLUSION—THE ISRAELI NEGEV
Water losses are not something we have to accept. The technology and methods exist to reduce them to insignificance. “According to 2010 reports, the average NRW rate in Israel is 12.9%…this value is composed [of] 2% of physical NRW caused by leakages and pipeline bursts and [of] 10.9% administrative NRW mainly caused by lack of public consumptions registration, inaccurate water meters, lack of water meters and illegal connections to the water supply network leading to illegal consumption.” (Source: Yoav Yinon, “Documentation of Best Practices in NRW Management – Case of Israel,” Documentation of Best Practices in Non-Revenue Water Management in Selected Mediterranean Countries, Sustainable Water Integrated Management (SWIM), February 2013.)
Think about that. Israel experiences less than 13% water supply losses, of which only 2% are from actual physical leaks. The world average for non-revenue water losses is almost 37%. The average city water utility in the US experiences 30% non-revenue water losses. Israel certainly has the most efficient water supply system in the world. What can they teach the rest of us about managing and preventing water supply losses?
Being a very dry country (with an average of only 23 inches of rainfall each year—an amount that has fallen by half in the past few decades), Israel had to become a technological leader in water management out of necessity. Its population has grown tenfold in 70 years to 8 million people and now has a water surplus. Having a secure water supply was essential for national survival and its advancement has provided a tool for bringing peace to its neighbors. In doing so, Israel has set the gold standard for water management and given an example for the rest of the world to follow.
From the very beginning, Israel directed its scientists and engineers to come up with methods for reducing water consumption and water waste. As early as the 1950s, Israel was already treating its sewage water and reusing it for agriculture. Currently, 95% of Israel’s sewage is purified and 85% is reused. Most of this water is used by agriculture. Israel has literally made use of every drop through the invention of drip irrigation. As a result, no farm in Israel needs to use flood irrigation methods—a standard, if wasteful and inefficient, practice in the rest of the world. No agricultural industry anywhere in the world, including California, can match Israeli water technology.
By developing more salt-tolerant crop species, Israel has reduced the demands on desalination efforts and allowed for the use of more saline soils. And Israel remains a world leader in desalination as well. Its desalination technology is so advanced and widespread that desalinated water makes up 94% of water used for domestic consumption. It doesn’t just desalinate seawater, Israel also treats brackish groundwater to make it usable.
On a more human scale, but no less advanced, are Israel’s management techniques for minimizing non-revenue water losses. These include:
- Implementation of administrative water loss surveys through customer interviews, which allows the water supplier to fully understand the elements of the water distribution system and determine which contribute the most to potential non-revenue water losses.
- Performing through physical surveys to locate leaks and other locations of losses as a guide for maintenance, repair, and future capital investment for system improvements. Together with the customer surveys, physical surveys are their first line of defense against water loss.
- The use of pressure management and system modeling to improve network performance (getting the most water to customers with the least amount of energy expended or water lost) while preparing for future rehabilitation efforts.
- The installation of new meters and replacement of old faulty meters allowing for better understanding of water usage by managers in specific sections of the distribution network.
- Pressure management reducing the actual physical losses by reducing the driving head on existing leaks and reducing the consumption of energy (especially effective in mountainous terrain).
Sewage Treatment Plant, in the Sorek Valley, Israel
From California to Africa to the Middle East, drought poses a major threat. In the past, simple changes in rainfall patterns were enough to snuff out a civilization. And in many ways, our hyper-connected, complicated civilization is more vulnerable to climate changes than past civilizations. But it also possesses the knowledge and the means to prevent the worst from happening, preserving every drop of water from loss. “Waste not, want not,” goes the old saying. With these technologies we should never have to want for water.
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Since 2015, one of their most effective programs is their Water Optimization and Low Flow Program (WOLF). This is an innovative training and support program designed to assist selected companies and utilities in developing water efficiency programs for their customers. WOLF has been a positive response to drought conditions in the American West and has expanded nationwide. It applies their comprehensive knowledge of water efficiency and years of experience gained from field testing, lab testing, relentless research, and thousands of water efficiency programs to the problem of water conservation. Organizations joining the WOLF program can partner with Water Management Inc. to educate themselves on water conservation and utilize their resources to improve water efficiency. Starting with a Desktop Water Assessment (Water Assessment Process) to quantify where the greatest opportunities for savings exist, specific sites are selected for onsite inspections and audits. These teams utilize specialized water auditing tools, including the T5 Flush Meter, to obtain data on water usage and the current state of their water system infrastructure. With this information, fixture replacement costs can be calculated and potential operational savings identified, including ROIs and IRR (internal rates of return) for each proposed water conservation measure. These final savings models provide a path forward for their partners. Variations of the basic WOLF program include WOLF Water Provider, WOLF Installer, WOLF Property Management, and WOLF Diagnostician.