Has Your Drinking Water Usage Decreased?

Did You Know?

Reduced or discontinued water use in buildings and water systems can result in both microbial and chemical health risks to occupants. Microbial risks include total coliform, E. coli, and/or legionella, while chemical risks are primarily lead.

To minimize the potential health risks of stagnant water in closed parks or reduced-occupancy buildings, the following guidance is recommended during periods of reduced use and before the building or park returns to normal use.

Flush the System Occasionally

During Reduced Use: The building and park water system plumbing should be flushed occasionally. This helps prevent mineral and microbe build-up that could be hard to remove in one single flush of a system before normal operations commence.

Before Normal or Full Occupancy: The building and park water system should be thoroughly flushed. Begin flushing at the meter (water systems receiving water from municipal water systems), water source (well, spring), or point of entry into the building or park water system. Flush all fixtures and lines in the water distribution system including all showerheads. Flush away from the meter or sources as you go through the building or park water system.

Always flush until there is new water throughout a building or park water system. Flushing from the point of entry or source out to the ends of the plumbing system can help ensure new water is distributed throughout the system.

Drain Storage Tanks

Consider draining any storage tanks, including water heaters and softeners, to ensure turnover using manufacturer protocols for routine maintenance. Check for sediment that may have collected during the stagnation period. Depending on the quality of the water, water water should be no more than five days old.

For example: you have a 10,000 gallon water storage tank and only use 1,000 gallons a day and believe the tank does not mix well with new water. Since you’ve only used 5,000 gallons in five days, it is a good practice to flush the tank every five days. If you have questions, feel free to ask your regional public health consultant.

Remove Equipment That Can Be Clogged

Particles can be released during flushing and may clog aerators, filters, showerheads, and other mechanical equipment. You should remove these before flushing or clean them after flushing. Backwash filters after flushing.

Measure the Chlorine

The presence of chlorine in the cold-water supply is an indication that new water is distributed throughout the system. NPS RM83A (section 7.3.1) requires all potable water systems have a minimum chlorine residual of 0.2 mg/L unless they have a waiver approved by the NPS Office of Public Health.

A chlorine residual test, measured at the furthermost outlet, will show whether chlorine is present. Most park-operated water systems should be and are tested daily.  There are several companies that sell chlorine test kits.  Before ordering, double check that your water system uses chlorine as a disinfectant.

Here are a couple of options for test kits from Hach. There are other options if you want to research).

Ice Machines

Ice machines should be cleaned using manufacturer protocols. After flushing, dump the first three batches before allowing the public or employees to use the ice.


As a reminder, park drinking water systems should check bacteria levels in water systems at least once a month and provide results to your regional public health consultant. More information can be found in NPS RM83A.

For More Information

The Centers for Disease Control (CDC) provide many resources for water and wastewater concerns:

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