When unaccounted for water kept rising in Des Moines, Iowa, Water Works officials knew they had to find a way to reverse the trend and improve the system.
Leak detection using ultrasonic equipment and follow-up testing, along with a scheduled plan of “listening” to the entire system, has cut water loss almost in half. The program has been so successful that neighboring agencies have enlisted the aid of Des Moines Water Works to conduct similar programs for them. Being a good neighbor and sharing skills has created a new profit center for the agency and is helping the region conserve water and energy.
Pinpointing losses
The Des Moines Water Works provides water to about 400,000 people and operates some 1,400 miles of distribution lines. The Water Works was no stranger to using sound-based equipment to detect leaks in its system, which includes a mix of cast iron, ductile iron, PVC and concrete pipe. The agency had been using various forms of the technology since 1983.
When the agency looked for the most logical method to reduce unaccounted-for water, ultrasonic listening equipment stood out as the most cost-effective method. The staff decided to use two types of “listening” to assess the system thoroughly on an annual basis: a conventional valve survey and a hydrant top survey.
For the conventional valve survey, crews use an ultrasonic leak detector by Fluid Conservation Systems. The ultrasonic listening device is lowered into the valve box and attached by a magnet to the valve top. The crews then listen for the distinctive sound that leaks. If they record no sound, they seal the valve access and move onto the next survey point.
All points surveyed are then color-coded: blue for no sound, green for a slight sound, and red for a strong leak sound. This information is given to the Water Works GIS department and is logged into a Bentley Water GIS database for analysis and to determine the next steps.
With a hydrant top survey, the same principles apply, except that the device is set directly on the top of the hydrant. The system is divided into two sections and crews perform valve surveys on one half and hydrant top surveys on the other. They alternate survey types each year.
“The sound that comes through a hydrant has to travel from the water main, through the hydrant branch and then up through the hydrant for the technician to hear it, so it’s a little less effective,” says Ted Corrigan, director of water distribution. “It’s a much faster survey, and the crews can get a lot accomplished, but we sacrifice some sensitivity and effectiveness so we don’t want to rely on that alone. Alternating the survey types covers the system and ensures that all the assets are assessed accurately.”
For the survey schedule, the system is broken into five territories, each divided into two groups — one for each type of survey to be performed. “We devised this plan because we have crews working throughout various territories in our system performing utility locating services,” says Corrigan. “When these staff members’ duties allow, they assist with hydrant top surveys. By using a zoned work flow, we ensure that there is hydrant top survey work available in every territory each year for the utility locating teams.”
All sounding results for both surveys are compiled and analyzed. Assets producing leak sounds are scheduled for a follow-up survey using a TriCorr 2001 Correlator by Fluid Conservation Systems. Two connection/sounding points are required for the correlator to pinpoint a leak. This is accomplished by using two outstations called MP90s that have sensors that can identify sound. The MP90s are set up on each side of the suspected leaking line, either at two valves or at a hydrant and valve or directly on the water main using probe rods.
The difference in intensity of sound is processed through computerized analysis equipment that correlates the sounds from the two points and pinpoints the leak based on the sound intensity produced. The data collected in this assessment is used to schedule the appropriate plan for repairs.
Proof positive
“At the start of this program, our best information sources indicated our annual lost water was around 15 percent, and now that is down to 5 to 7 percent,” says Bryant Stump, water distribution supervisor. “That equates to more than one billion gallons of water saved per year.”
The program also provides benefits in time savings and efficiency. Although the purpose of the program was to reduce unaccounted-for water, it has blossomed into a tool the department can use to pinpoint the locations of leaks to within one foot.
“We decided that we’d use our leak detection method in advance of a main break repair,” says Corrigan. “When there is water coming up, we dispatch the leak survey team to pinpoint the location before we start digging. This has proven to be a very successful tool in saving us a lot of time and effort on our main break repairs.”
The news of the Water Works’ success began to spread to neighboring communities, and agencies began asking the Water Works to provide similar surveys for their systems. The Des Moines team was willing to help and, with careful planning and scheduling, was able to do so without increasing the budget or staff.
Although most neighboring agencies employ the Water Works on an as-needed basis for pinpointing a specific leak or issue, three surrounding municipalities have contracted the Water Works to perform full-scale surveys similar to its own, follow up and identify all the leaks heard, and perform pinpoint correlation location services. One-time leak pinpointing services are charged at $140 per hour, and comprehensive leak survey programs averaging $65 per hour.
All this work is performed by one full-time leak surveyor, one full-time field service technician who pinpoints leaks and performs correlation surveys, and six field service technicians who perform hydrant top surveys as part of their normal workload in their assigned territories. The technicians are on call for a week at a time to handle emergency leak locations outside normal business hours.
The services performed for other cities have generated on average $30,000 in annual revenue, helping to offset the Water Works’ own program costs, which range from $80,000 to $100,000 per year.
Improving the system
As in most municipalities, keeping up with replacement of water distribution mains is a constant challenge. The Des Moines Water Works has an aggressive priority replacement program and replaces a portion of the lines each year as part of its capital improvements budget.
Old lines are replaced with PVC pipe, which creates a challenge for the leak detection teams. “One of our biggest challenges going forward is going to be accurate leak detection on our newer assets,” Corrigan says. “Our leak detection equipment is not as effective on PVC pipe as it is with metal pipe.
“As we have been installing almost exclusively PVC distribution mains for replacements, we are faced with finding other methods that can provide the accuracy needed on these lines. PVC doesn’t present as many issues as cast iron, which is promising, but we are always finding ways to work around the technology’s limitations.”
One method used with PVC lines is to listen not only to the valves and hydrants, but to service lines, as well. Typically, on cast iron mains, technicians do not need to “sound” service lines, since the sound of a leak carries well to the valve. By covering all the bases with PVC pipe, the crews have a better chance of catching potential problems.
On newer installations or newly replaced lines, the crews perform a post-inspection after construction, sounding all the valves, hydrants and any service lines. Two years later, they sound everything again. Thereafter, they survey only the valves and hydrants each year. The agency is considering modifying the frequency of the surveys from two years to five, as crews are finding fewer leaks in PVC lines.
Another method being considered to augment sounding surveys on concrete pipe is non-destructive testing, using remote current technology provided by Pressure Pipe Inspection Company. The testing requires significant effort, but the Water Works believes these extra efforts could help avoid catastrophic failures that have been seen in other parts of the country.
Just do it
Reducing leaks, conserving water and improving the system have been the results of the Water Works program. Whether a utility wishes to develop its own program or “ask a friend,” Corrigan and Stump agree that the right equipment and training are the keys to success.
They offered their words of advice. “Quality equipment and actually training your staff — getting buy-in — these are important and worthwhile investments,” says Stump. “It sounds easy to go out and listen for leaks, but there’s a lot of training involved in getting accurate data that you can use. Equipment manufacturers do have training programs for this technology, and if it is offered, take them up on it. It will help your crews tremendously.”
The Water Works program, with its employee training program and quality equipment, has been a small investment in relation to the dividends. “This program saves us around $250,000 a year, which is more than the program has cost us so far. It is a simple method that’s highly effective and worth serious consideration for anyone trying to conserve precious resources and reduce costs while delivering a quality product to the customer.”
