|Maintaining Distribution System Water Quality
Tips for keeping high quality water flowing through your system
by Jeff Oxenford, Training and Technical Services Specialist (RCAP)
Just because you produce high quality water at the treatment facility doesn’t mean that your job is done. Maintaining water quality throughout your distribution system is also essential. Studies have shown that over 1/3 of waterborne illness originated from problems in the distribution system.
Water quality in the distribution system can degrade for a variety of reasons including, contamination from an uncontrolled cross connection, contamination during storage, or high water age leading to degradation of water quality. Events such as a main break or loss of system pressure can also allow contaminated water to enter the distribution system. So, as an operator, what should you do? Below are 11 items for you to consider.
1. Ensure that you are maintaining a disinfectant (chlorine or chloramine) residual throughout your distribution system. While regulations only require that residual samples be taken at the same time as coliform samples, taking additional non-regulatory samples can help you identify a problem or just better understand your distribution system. Placing data on a map helps you identify potential problem areas with low residual.
2. Manage the water age in your system. AWWA recommends that water age should not exceed 5-7 days. In essence, the longer the water sits in your distribution, the greater the chance it can degrade. Develop strategies to keep water moving in your system.
3. Routinely inspect your storage facilities. A missing screen on a vent, an improperly closed hatch, a crack in the tank wall, or any other unscreened opening can allow for an insect, snake, birds or other critter to enter your storage facility. If anything or anyone tries to access your tank, you want to know.
4. Maintain system pressure. Pressure in your system keeps contamination out. Average pressure should be above 35 psi, and during emergencies above 20 psi. If you lose pressure, contaminated water can enter through any leak or cross connection. Requirements vary from state to state, but, in most cases, if you lose pressure, you must issue a boil water notice. Routinely monitor pressure throughout your system.
5. Have a cross connection control plan and implement it. Cross connections are one of the leading causes of contamination in the distribution system. You need to be vigilant to control cross connections as new cross connections occur every day. Backflow prevention devices need to be routinely inspected.
6. Flush your system. Flushing is a valuable way to clean your water lines by removing deposits and reducing water age in dead ends. Develop a unidirectional flushing program, which is a systematic method of flushing that cleans water lines from the plant outward (large pipes to small pipes).
7. Listen to your customers. When customers complain, more often than not, something is going on in the distribution system. Investigate and keep track of customer complaints.
8. Plan for emergencies. Water main breaks or pump failures often happen at the worse times (middle of the night, during holidays, etc.). Having an emergency response plan and exercising it can help you save valuable time in an emergency. Always ask yourself, “What if. . .?”
9. Listen. Any time you touch a valve or hydrant, listen for leaks. The more you listen, the better you understand your system. Leaks don’t get smaller, so if you hear something, schedule a repair. Consider the implementation of a leak detection program to find non-surfacing leaks and to reduce unaccounted for water loss.
10. Have standard operating procedures for all your routine and emergency procedures. Procedures should include preventive maintenance programs, such as valve exercising as well as a hydrant inspection and maintenance program.
11. Be proactive. Water quality only gets worse with time in the distribution system. Collecting, analyzing, and maintaining data allows an operator to stay ahead of problems.