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Solutions for Cities

A. Leak Detection and Repair Strategy

Reducing leaks and losses is a critical part of any utility's water efficiency strategy. While the best water utilities have water losses of up to 10 percent, this figure goes as high as 50 percent in many systems. A review of 54 developing country projects financed by the World Bank found the average water loss in water supply and treatment was 34 percent.

A comprehensive leak detection and repair strategy allows the utility to take advantage of the information gleaned from loss accounting by coupling it with specific action to reduce losses. This strategy may include regular on-site testing using computer-assisted leak detection equipment, a sonic leak-detection survey, or another acceptable method for detecting leaks.

In addition to the physical water losses, another effect of leakage is the reduction in system pressure. The double jeopardy of major leakage problems lies in the fact that not only does the system require more water to actually meet consumer demand, but also because leaks also cause pressure loss, system operators may be forced to increase system pressure. The pressure increase not only wastes energy by supplying more pressure than is really needed, but it also further exacerbates the leakage.

Leak reduction can involve pipe inspection, equipment cleaning, and other maintenance efforts to improve the distribution system as it currently operates and prevent future leaks and ruptures from occurring. Just replacing a valve or sealing a joint can provide substantial financial benefits. To reduce non-leak related losses in system maintenance, utilities can consider methods for minimizing water used in routine maintenance procedures. (See information on the potential for Galati's leak reduction program).

Seepage from canals is a common water loss problem for both rural and urban water systems. Both canal lining and piping can reduce seepage. Unlined canals often lose 30 to 50 percent of water, depending upon the type of soil, but a well-operated and lined system can reduce losses to under 10 percent. Using buried pipes rather than canals can similarly result in distribution efficiency improvement on the order of 30 percent.

B. System Piping Redesigns

System piping redesign can offer several potential efficiency improvements. First, municipal water authorities may be able to remove a pump by taking advantage of gravity. In addition, systems can be developed to reduce or eliminate the need to pump water at expensive peak hours by creating additional gravity-fed storage units. Also, since much of the energy to be used in moving water is actually expended in battling friction in the water lines, the conscientious selection of pipe sizes, pipe materials, valves, elbows, and other system components can have a tremendous impact on efficiency by reducing friction losses in the pumping system. One water utility in India made very impressive gains by switching to PVC plastic piping.

Furthermore, selection of inappropriately-sized equipment for normal operation is another major redesign opportunity that stems from system designers overestimating the needed capacity to meet highest flow conditions. Operational problems of over-design can include excess flow noise, pipe vibrations, and poor performance. Over-design can also result in unnecessarily large costs for materials, installation, and operation.

Corrections to over-design include:

  • Installing a correctly-sized pump
  • Installing a adjustable speed drive motor
  • Reducing impellers
  • Adding a smaller pump to reduce intermittent operation

The effect of any of these changes is to reduce energy losses, and hence operational expenses, in the existing system.

C. Equipment Upgrades

Upgrading to newer, higher efficiency equipment such as pumps will likely improve system performance if they are correctly sized and integrated into the entire water system. System enhancements can also be gained through the proper application of:

  • Variable Speed/Variable Frequency Drives
  • Impellers
  • Lower friction pipe and coatings
  • Capacitors

For the most part, proper equipment installation and application will result in savings for energy, operations, and maintenance. However, in some cases, the facility will need to assess trade-offs that will exist between different scenarios of increasing and decreasing the costs for energy, operations and maintenance.

Impellers: Another alternative to improve efficiency is installing a smaller impeller or trimming the impeller in the existing pump. An impeller is the spinning component in a centrifugal-type pump that pushes fluid through the system. Similar to the VFD motor, a smaller or trimmed impeller decreases the speed of the fluid to reduce energy losses.
Lower friction pipe and coatings: Pipes made of smooth material such as polyvinyl chloride, versus traditional cast iron pipes, can reduce friction losses. Lower friction pipe can increase energy savings by 6-8 percent. Applying certain resin and polymer coatings to the insides of a pump can achieve another 1-3 percent improvement. Coatings can also reduce erosion and corrosion in pipes and pumps

Capacitors: Installing capacitors can reduce the energy required to run certain equipment. Capacitors are devices that store electrical energy and are used to correct low power factor. Low power factor is caused by certain electrical equipment that create magnetic fields in their operation, such as transformers, motors, and high intensity lighting. Often this equipment represents a major portion of the electricity used at a facility. A problem low power factor can cause is premature equipment failure. Additionally, electric utilities often levy penalty fees for low power factors, so use of capacitors may avoid unnecessary expenses.

D. Maintenance and Operational Practices

Many facility improvements require little or no investment in new equipment. Often one of the most cost-effective efficiency tools for municipal water authorities is to develop maintenance systems and operational procedures that promote water efficiency.

Maintenance and operational changes may require staff training and institutionalization of certain tasks. Beneficial practices might include:

  • managing system at appropriate pressure that meets system flow needs without excessive pressure.
  • Surveying equipment and piping for leaks.
  • Replacing cracked water mains and fixing manholes.
  • Checking meter accuracy.
  • Cleaning equipment periodically.
  • Identifying and replacing inefficient equipment.
  • Switching off wastewater treatment equipment, motors, HVAC and other equipment not in current use.
  • Using water storage and hours of operation to reduce peak system operation requirements.
Reduction of the system water pressure has several positive impacts on system efficiency. It can decrease leakage, the amount of flow through open water fixtures, and decrease stress on pipes and joints, while extending the life of equipment, and decreasing system deterioration and the need for repairs. Small water customers with system pressures greater than 80 pounds per square inch (psi) should be reviewed as a potential water pressure reduction candidates, as long as any reduction does not compromise the quality of service to the customer.