Introduction: Distribution System Maintenance


Distribution systems must be operated properly in order to safeguard the public health and public safety.

As you’re aware, a water distribution system is a network of storage tanks, valves, pumps, and pipes that carry finished water to consumers. It must be operated properly in order to safeguard the public health, public safety, and provide safe and clean water to customers’ taps. Once water is pumped from a well, or leaves the treatment plant, its quality must be maintained throughout the distribution system.

As the water system operator, it is your responsibility to ensure sufficient disinfectant residuals are present at all points throughout the distribution system. You must be disciplined when taking bacteriological (BacT) samples to ensure they are representative of the water customers consume. Twice a year, you will need to flush the mains. Once a year, you will need to conduct a pressure test, a valve exercise, a fire hydrant inspection, and a storage tank inspection. These should all be scheduled into your maintenance calendar. 

 

More information related to Introduction: Distribution System Maintenance:


Bacteriological Sampling Procedure

When you collect a bacteriological sample, you must follow a set of procedures. First, allow the water to run for five minutes to flush the service line before sampling. After the line is flushed, fill the sample bottle to the shoulder, leaving a one-inch air space at the top. Follow the sampling requirements specified by the lab EXACTLY.

Once you have the sample bottled, complete the following information in waterproof ink: Include the county from which the sample was collected; the PWS ID number and the name of the system; who will be charged for the sample examination; and the collector's name, title, certification number, organization, and telephone number. Also include the return address for the examination results. Do not write “same as above” in this field.

You must also complete the sample collection date, which includes the sample type (repeat and replacement samples must have the complete lab number for the previous sample). Also include the date and time of the sample collection. The collector must initial this form. You must give a specific description and location of the sampling point. Indicate whether the water supply is chlorinated, pH level, and how and in what condition the sample is to be transported to the laboratory.

Send your sample in a manner that ensures it arrives at the lab within 30 hours of collection, and consult with the laboratory to determine which days and at what times you should send your samples. Five copies of the completed sample history form must be included with the sample.

Bacteriological Sampling General Procedures

Bacteriological sampling procedures contain a lot of DO NOTS. Following are general procedures for collecting bacteriological samples.

  1. Use only sterile bottles furnished by the State or County Health Department. These sample bottles have a shelf life of 6 months, after which they must be returned to the Office of Laboratory Services for reprocessing.
  2. Do not touch the inside of the sample bottle or cap.
  3. Do not collect samples from a storage tank, leaky faucet, aerators, or “purifiers”.
  4. Allow cold water to run 5 minutes to clean service line before sampling.
  5. Do not rinse out the bottle.
  6. Reduce water flow and fill bottle to the shoulder, leaving about 1 inch air space at the top to facilitate mixing. Samples can be rejected at the laboratory for insufficient air space.
  7. Replace the sample bottle cap securely.
Pressure Testing

After the trench has been partially backfilled (joints left uncovered), new pipes must be pressure tested for leaks. This is accomplished by filling each valved section slowly with water (no greater than 1 foot of pipe per second), while releasing air through corporation stops, or water service shutoff valves, and hydrants.

Once filled with water, the pipe should be allowed to sit for at least 24 hours. After 24 hours, the test begins by increasing water pressure to 150 psi or 50% higher than the normal expected pressure, whichever is larger. This pressure must be maintained for 4 hours and any pressure loss during this time indicates leakage. Measure the amount of water needed to refill the pipe. Visually check joints for leakage and repair or adjust as needed. Some leakage is allowable, and the amount varies by pipe material. Check AWWA standards for allowable leakage for different types of pipe.

Annual Valve Exercise

It is important to exercise all valves in the system at least once a year to ensure that you can locate them and that they can be opened and closed properly during emergency shut-down periods. Exercising valves means completely closing and then opening the valve manually to assure they close tightly and operate properly. Develop a map that identifies the type of valve and location. Record the number of turns it took to close the valve. Record if the valve is right- or left- hand and whether the valve is normally closed or open. Correct valve deficiencies, replace valves when necessary, and record the work and/or changes in your valve records and on distribution system maps. Keeping detailed records will ensure better operation in the future, and will help you locate and operate valves quickly in an emergency.

Annual Fire Hydrant Inspection

In order to protect the public safety, fire hydrants must be maintained and kept in good working order. Water system personnel must work closely with Fire Department personnel to ensure hydrants with operational problems are identified and repaired or replaced in a timely fashion. Inspect hydrants at least once a year and perform the following maintenance tasks:

  • Observe the general conditions of the hydrant—cracks in the barrel, worn threads, etc. Replace or repair as needed
  • Cut down any overgrowth and repaint the hydrant if necessary
  • Exercise the hydrant valves, lubricate the threads, and confirm the street valve is open
  • Locate and exercise the street valve. Repaint the street valve cover lid if necessary
  • Open and lubricate the stem valve with light grease if accessible
  • Close the hydrant stem valves
  • With the hydrant valve(s) closed, open the caps and verify the presence of gaskets. If missing, replace. Lubricate the threads with light grease
  • With the caps off, crack the hydrant stem valve(s) and flow some water to verify that the street valve is open and to clean out any debris in the hydrant. One valve must be fully opened and flowed for at least 1 minute. If the street valve is closed, water will come out of the hydrant initially, then stop. If the street valve is open, water will flow until the hydrant valve is closed
  • Replace the caps
  • If the hydrant is inoperable, clearly mark the hydrant with an out of service tag and immediately notify fire department personnel
  • Record observations and maintenance in your fire hydrant log
     
Annual Storage Tank Inspection

All storage tanks should be inspected at least annually to ensure that they are protected from contamination. Visually inspect your storage tanks to see if there is a problem with sediment buildup or a possible breach in any of the tanks. Over time sediment builds up in almost all water storage tanks. Storage facilities should be taken out of service, cleaned, inspected, and disinfected prior to return to service at least once every three years. Washing out the tank annually is recommended when water supplies have sediment problems. Although, the most common storage tank breach you’ll probably find is missing or corroded vent screens. Screen any openings to stop the entry of small animals, small insects, and other organic matter. Screens should not be blocked or torn. Screens should be in place on vents and overflows (or a flap gate on any overflows). During your inspection, check that hatches are properly sealed and locked. Also note any deterioration in the tank’s walls or the tanks foundation.

The Introduction: Distribution System Maintenance slide is featured in the following lessons:


Distribution Systems

Duration: minutes
Level: