Current Water Loss Management Practices

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The starting point for successfully managing water losses is to accurately assess water supply and consumption volumes by conducting a standardized IWA/AWWA water audit. Many water audits are performed by utilities in the United States annually, but they lack uniformity. The audit methods used, the performance indicators and expressions of water losses calculated, and the time intervals between audits vary significantly from utility to utility. The majority of water utilities do not use the IWA water audit methodology recommended by the AWWA Water Loss Control Committee (WLCC). Therefore, it is impossible to accurately compare water losses between utilities since the assessment is not uniform. The historic indicator used to describe water losses (% volume of nonrevenue water) is highly unreliable and inappropriate. This percentage is unduly influenced by the denominator (system input volume) resulting in understated losses for water utilities with growing populations and overstated losses for utilities with contracting populations. Also, this simple percentage reveals nothing about specific loss volume quantities and costs, which are two of the most important parameters in the analysis.

The following simplified example clearly demonstrates how misleading and inappropriate percentage figures are when used as performance indicator for water loss management. In our example, we look at a standard U.S. water utility with 20,000 residents (no commercial or industrial customers) and an average per capita consumption of 400 gal/cap/d with a total metered consumption of 2920 mg/year. Assuming the utility has 325 mg of real losses per year the utility has a total system input of 3245 mg/year. The percentage loss figure for this utility is therefore 10%. If the same utility reduces the per capita consumption to 200 gal/cap/d through a successful demand side conservation program the total yearly metered consumption is reduced to 1460 mg. With no reduction in real losses the total system input is therefore reduced to 1785 mg/year, which results in a percentage loss figure of around 18%. This simple example explains why expressing water losses as a percentage of system input volume is a poor performance indicator.

North American utility with typical per capita consumption of 400 gal/cap/d:

Total system input volume: Total consumption volume: Total losses:

3245 mg 2920 mg 325 mg

Percentage of losses as % system input volume: 325/3245 mg = 10% Same utility in with per capita consumption of 200 gal/cap/d:

Total system input volume: Total consumption volume: Total losses:

1785 mg 146G mg 325 mg

Percentage of losses as % system input volume: 325/1785 mg = 18% Figure 4.3 provides another example highlighting the weakness of the percentage indicator (in this case, metered water ratio) as it shows little variation despite a significant reduction in nonrevenue water over the 12-year period as shown by the trend line. This occurs since consumption in Philadelphia has also been in decline.

The current lack of structures, regulations, and uniform assessment methods of water losses contribute to the fact that water loss management is still a rather weak and neglected discipline in the United States. The AWWA survey "Survey of State Agency Water Loss Reporting Practices" and the AwwaRF report "Leakage Management Technologies"4 both clearly highlight that most water utilities employ only reactive leakage management, which consists solely of repairing broken or burst water mains and leaks that have caused customer complaints and/or became visible on the surface.

Broken water mains are the most recognizable example of a reported leak, which, due to their damage-causing nature, are usually quickly reported, responded to and contained. However, unreported leaks, which frequently escape the attention of the water supplier and the public, account for larger amounts of lost water since they run undetected for long periods of time. While most water suppliers in the United States provide reasonable response to reported leaks, those that conduct regular unreported leak searches, or leakage surveys, (usually at 1- to 5-year intervals) probably represent a minority of the country's systems. Many systems conduct no surveys to detect unreported leaks. Generally, only the larger water systems employ specific "leak detection" personnel and purchase sophisticated leak correlators or other electronic equipment. Smaller systems typically rely upon leak detection consultants to provide pinpointing

Philadelphia Water Department Nonrevenue Water vs. Metered Water Ratio

i=i Nonrevenue water, mgd ♦ Metered water ratio, % — Linear (nonrevenue water, mgd)

i=i Nonrevenue water, mgd ♦ Metered water ratio, % — Linear (nonrevenue water, mgd)

Philadelphia Water Loss

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Fiscal year

Figure 4.3 Nonrevenue water vs. metered water ratio. (Source: George Kunkel.)

100.00%

90.00%

80.00%

70.00%

%

,io

60.00%

atr

ter

50.00%

at

w

40.00%

d re

ter

30.00%

et M

20.00%

10.00%

0.00%

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Fiscal year

Figure 4.3 Nonrevenue water vs. metered water ratio. (Source: George Kunkel.)

services for hard-to-find leaks and to conduct periodic surveys of their systems to search for unreported leaks.

More sophisticated leakage management technologies such as district metered areas (DMA) or flow-modulated pressure control are only used by a handful of utilities in the United States.

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