Water Loss Determination: For What it's Worth

By Joan Kenny
Kansas Water Office and U.S. Geological Survey

The standing-room only crowd at the KRWA session on Water Loss Problems last March is one indication of how important this subject is for water providers. It's easy to understand that controlling water loss saves money, but it's not always easy to determine what your water loss is, why it's there, or how to reduce it. What's more, water loss awareness is a never-ending job, and one that is as individual as each water supply system. This article summarizes the main concepts in water loss determination, suggests ways to keep loss under control, and describes some of the reasons why water loss determination is essential to good management.

In my work for State water agencies, I have looked at countless annual water use reports from systems of all sizes and from all parts of Kansas. The only thing that's certain is that each report is different. I've also had the opportunity to meet or speak to many operators, bookkeepers, city clerks and public works superintendents who provide information for the water use reports. The one thing they have in common is a great attitude about their work. I'm always impressed with how well these people handle the challenging tasks of operating a water system. Because of their efforts at keeping water records, we all know more about identifying water loss.

What is water loss?

Simply put, water loss is the difference between the water entering the supply system (through wells, surface intakes, and/or wholesale purchases) and water used (sold to customers or used for free). All systems experience some water loss as an ordinary part of operation. Water loss is also called 'unaccounted for water' to distinguish it from losses that occur for known reasons, such as for water treatment processes or hydrant flushing. Amounts of unaccounted for water are typically expressed as a percentage of the total amount pumped and/or purchased. In 1997, unaccounted for water among systems that completed water use reports ranged from less than 3% to more than 65% of the total amount. The average was 15%. What is a reasonable percentage for your system depends on the type of treatment required, the condition of your system, and how much of your use is metered. The American Water Works Association recommends that the loss occurring after treatment be maintained at 10% or less.

How do I calculate water loss?

The first thing to do is to have believable figures. There's no use chasing down leaks if your master meter is grossly overregistering, or if your sales figures are erroneous. Periodically test raw, finished, and wholesale meters, and keep them within 2% of actual flow. Check that all metered uses have been properly accounted for. Correct misreads promptly, and make sure any necessary conversions from cubic feet to gallons are correct. Also, record the actual usage at each metered location even if the gallons used are less than the gallons included on the minimum charge. Showing that more water was used than actually passed through the meters will obscure your true water loss and may even result in an apparent negative loss. (Underregistering master or finished meters can also cause an apparent low or negative loss, which doesn't help you detect real losses.) Try to compare production and usage for the same monthly time periods, if possible. Water loss percentages may show more monthly variation if service meters are read in several cycles, if customers read their own meters, or if there is a combination of wholesale water sources each with different meter reading dates. Rural water districts with self-read meters should check those meters at least annually to catch up with delinquent payments and amounts of water used.

Records of water produced, purchased, sold to wholesale and retail customers, and used for free are the basis of annual water use reports. Maintaining such records is useful even if the State isn't asking you to do it. Subtract metered uses from the total amount pumped and/or purchased on a monthly basis to figure the amount of unaccounted for water as a volume. Divide this number by the total to get the percentage. Monthly comparison of water in and water out is the key to monitoring water loss. A graph or table showing the amount and percentage of unaccounted for water each month of the year can be a good way to present information to your city council or rural water district board. Of course, sudden large losses often are detected in the short term by noticing changes in daily pumpage.

What are common reasons for water loss?

Water loss can occur at many different points in a system, both pre- and post-distribution. It's important to ask what areas of a system you are determining water loss for, then obtain reliable information on water quantities at all appropriate locations.

On the State water use reports, withdrawals are reported from the point where water is taken from the source, and loss is computed on the basis of that entire pre-treatment amount. If you pump from wells, it is important to meter any loss from lube lines and to make sure that check valves are not letting water flow back down the wells after being metered. If there is some distance between the points at which water is initially metered (such as at a well, lake, or wholesale connection) and a treatment plant, it is helpful to meter the water again as it enters the plant or tower to detect any losses occurring during transmission.

Water treatment often involves using water for backflushing, cleaning basins, and chlorine mixing. This water will show up as a loss unless it is metered. Accounting for treatment plant water use is very important for some systems, especially those using surface water. Some operators meter individual processes within a treatment plant; others simply meter the raw water coming in and the finished water leaving to arrive at the amount used in treatment. Of course, multiple meters can complicate matters when one or both is inaccurate. Keep good records of treatment plant use by reading and testing raw and finished meters regularly. If your meters are accurate and it still appears that more water is leaving your plant than is coming in, check that you are not metering some water twice. This can happen when finished water already metered is used for chlorine feed and then metered again going out. In this case, it would be helpful to meter the chlorinator water and account for it as you would any other metered use.

Losses occurring in the distribution system, after water leaves the plant or tower, are those most commonly associated with the term 'water loss.' These include leaks, line breaks, unmetered uses, and theft. The best way to determine the amount of water lost in your distribution system is to meter all uses, whether they are billed or not, and read the meters regularly. Leaks on the customer side of the line can go unnoticed if meters are only estimated. Substantial amounts of water can be used at free services such as parks, pools, and city operations. It may seem unnecessary to meter infrequently used connections at community buildings, churches, and bulk outlets, but without a meter you do not know how much water may really be used or lost at these locations. An unattended leaky toilet can waste a lot of water before it's discovered. Bulk sales recorded on the honor system are rarely accurate. Some towns have used tremendous quantities of water for irrigation of parks or a newly seeded ballfields. Accounting for as much usage as possible will help you identify the amount of water that is truly unaccounted for.

Other water losses cannot easily be measured, such as loss from tower repairs, tower overflows, line breaks, fire use, or flushing. It's a good idea to keep a log noting when any such losses happened, so that you know what to expect when you compare production figures with sales and find a large difference. Knowing approximately how much water is lost through flushing can help you determine whether the remainder of your unaccounted for water is really a problem. Some operators who flush hydrants frequently have portable meters for measuring amounts of water used, or they estimate the amounts by timing each flush at known flow rates.

In many cases, large water losses are not due to leaks but to underregistering service meters. As meters wear with age or high usage, many tend to stop moving at low flows. The result is a gradual decrease in amounts of water metered (and paid for), which can add up to a lot of unaccounted for water and lost revenue for a water system. If your records indicate significant water loss and there are no known leaks or unmetered uses, check the age, volume recorded, and accuracy of your service meters. A meter changeout program is an investment that will pay for itself.

Is my water loss a problem?

Whether or not your water loss percentage represents a problem that should be resolved depends on the volume lost, the cost of your water, and the causes of the loss. If you operate a very small system, a single line break or tower repair can represent a large percentage of the annual total pumped but not indicate a chronic problem. Sometimes it's helpful to look at an unexplained volume of water lost in terms of rate of leakage to determine whether there is a problem worth worrying about. For example, an unexplained loss of 500,000 gallons per year could result from a leak of less than 1 gallon per minute, which may be hard to find. When small volumes of water are lost, searching for the cause should be weighed against the cost-effective use of your time and resources.

Some people are more conscious of volumes of unaccounted for water because of high costs to purchase or produce it. In many parts of eastern Kansas, the cost of delivering water reflects the expense of building and maintaining a treatment plant or developing a new, regional source of water. A system with high costs for water has additional incentive to monitor water loss and may not tolerate as high a percentage of unaccounted for water as a system in which the water is inexpensive to pump.

Finding the causes of water loss in any given month or year can help you determine whether there is a problem that needs to be addressed. Losses from ordinary operations and repairs are to be expected. Operators who routinely flush hydrants can expect a larger percentage loss, especially if the systems are small. Other persistent losses may result from situations that need attention; for example, a leaky pool, a slow meter on your largest customer, a flawed billing program, or a faulty altitude valve on the tower.

What can be done to reduce water loss?

• Keep good figures on production and use, and review them regularly.

• Maintain appropriate lube line flows, and ensure that check valves are holding.

• Keep all meters in good working condition. Test raw, finished, and booster meters every few years or as warranted by conflicting readings. Replace customer meters on a regular basis.

• Meter all uses as practical, and read the meters regularly. Note the dates of any large unmetered losses such as line breaks, tower repairs, frequent flushing, and usage by road crews or fire departments.

• Maintain good tower control.

• Fix leaks promptly.

• Call KRWA for free help with leak detection. This service is partly funded through Kansas State Water Plan fees.

• Determine the cause of chronic leaks, such as those from old corroded lines or glue joints, and whether line replacement is necessary. A grant or loan to replace problem areas may be appropriate if the cost is outside your budget.

• Prepare a conservation plan (the Kansas Water Office will assist you with this for free), and then follow the conservation measures that you have chosen for maintaining an efficient system.

Why is all this important?

Lost water is lost money. If losses are due to underregistering customer meters, you lose revenue on water you paid to deliver. If losses are caused by leaks, you've lost the money it cost to produce or purchase that water. In some cases, curbing large water losses from leaks can save a town or district the cost of finding additional water sources.

Wasted water means wasted dollars. Since 1989, KRWA has completed 564 water loss surveys locating an annual loss of 2.387 billion gallons. The annual costs to purchase or produce this loss would have been $3.586 million.

Water loss percentages indicate to others how efficient your system is. This may be an issue if you are applying for additional water rights, contracting to purchase or sell water, seeking a grant or loan for system improvements, or trying to stay within established conservation goals. A high loss percentage may work against you if unabated waste is occurring, or it may work in your favor if you need evidence that replacement of leaky corroded lines is warranted.

Information is a powerful tool in the business of providing water service. Good records help you understand your system's own unique needs and recognize any problems that may occur.