Water storage tanks need to be periodically inspected and cleaned to help maintain good water quality in the distribution system, and to help extend the life of the tank. Regular tank inspections can also help to identify small problems that may develop into major problems that can create health related issues, lead to costly repairs or premature tank failure. Tanks that are not periodically cleaned can cause contamination events that can harm human health or can contribute to customers' aesthetic complaints.
Tank inspection and cleaning can be done by draining the water tank. Another option becoming more popular is using divers or remotely operated vehicles (ROVs). Whichever method is selected, testing of the water according to American Water Works Association (AWWA) C652 is required, except for coliform testing. Two consecutive samples collected 24 hours apart must show the absence of coliform bacteria as required by Illinois Administrative Code, Title 35, Sections 602.310 and 602.135. AWWA Standards are incorporated into Illinois Environmental Protection Agency (Agency) regulations by reference. This FAQ sheet does not fully describe all of the requirements of the Standard. The intent is to advise the water system of the Agency's acceptance of the Standard. Systems are encouraged to purchase AWWA C652 from the AWWA bookstore for use. Please contact an Illinois EPA regional office with any questions.
AWWA G200 'Distribution Systems Operation and Management' is a Standard for maintaining water distribution systems that water officials also may wish to have available.
How often should a water system inspect and clean storage tanks?
The inspection and cleaning interval can vary based on the type of tank and water quality. Generally, a water storage tank should be inspected at least every five years, or more often, depending on local conditions. Cleaning and repairs should be addressed based on the findings of the tank inspection. Additional inspections between maintenance intervals are encouraged.
Is an Agency permit needed to inspect or maintain a storage tank?
A permit is not required to inspect, clean, repair or paint a tank. However, a permit is required if any modifications are made to the tank such as, but not limited to, installing baffles, vents, hatchways, overflows or any type of mixing device. Contact the Division of Public Water Supplies, Permit Section at 217-782-1724 before starting any work if you are not sure if a permit is required.
What sampling is required for a tank that has been drained?
Disinfection of the tank using one of the three methods found in AWWA C652 is required. Following this procedure, samples from the tank must be analyzed for chlorine residual and coliform bacteria. If two consecutive samples collected at least 24 hours apart show the absence of coliform bacteria, and if the chlorine residual is acceptable the tank can be placed back into service. If not, continue sampling until two consecutive samples for coliform are negative. If necessary, the tank can be disinfected again. A boil order must be issued if the tank is placed into service before the required satisfactory samples are obtained.
Are tank inspections and/or cleanings that use divers or ROVs or cameras allowed?
Yes, underwater inspections that use divers or remotely operated vehicles/cameras are allowed. Cleaning as part of an underwater inspection is also acceptable.
Does the Agency need to be contacted when doing a tank inspection?
Water system officials are encouraged to contact the appropriate Illinois EPA regional office prior to a tank inspection or cleaning. Agency staff can answer questions and advise on the appropriate testing requirements.
Can an underwater inspection and/or cleaning be done while the tank is in service?
The Agency strongly recommends that the tank be isolated from the distribution system prior to personnel or a ROV entering the structure, unless operational conditions prevent this. An example would be a water plant with a single clearwell that cannot be taken out of service.
What sampling is required for an underwater inspection and/or cleaning where the tank is isolated from the system?
After the inspection and/or cleaning, samples from the tank must be analyzed for chlorine residual and coliform bacteria. If two consecutive samples collected at least 24 hours apart show the absence of coliform bacteria, and the chlorine residual is acceptable, the tank can be placed back into service. If not, continue sampling until two consecutive samples for coliform are negative. If necessary, the tank can be disinfected. A boil order must be issued if the tank is placed into service before the required satisfactory samples are obtained. Sampling the tank prior to the work is also recommended to establish baseline water quality.
What sampling is required for an underwater inspection and/or cleaning where the tank must remain in service?
For tanks that must remain in service, sample before the work, each day during the work, and after the work has been finished. Daily samples are required for chlorine residual, coliform bacteria and turbidity. Contact the appropriate Illinois EPA regional office if the chlorine residual drops below the required minimum level, if coliform bacteria are present or if turbidity increases. If sample results warrant, a boil order will be required until water quality is acceptable again.
What are any other requirements for conducting an underwater inspection and/or cleaning?
Refer to AWWA C652 for equipment and personnel requirements, safety requirements and disinfection requirements for equipment and personnel.
Can a coating be applied to a water tank during an underwater inspection?
Yes, as long as the product meets ANSI Standard 61 and is approved for application to wet or damp surfaces. Follow all manufacturer recommendations.