Reoccupying a Building After an Extended Closure

Guidelines for Safe Drinking Water

Lengthy periods of non-use cause water to stagnate in your pipes and degrade the water quality. One of the first things you will want to do when you reoccupy your building is to flush out the water sitting in the building's pipes with fresh water from the city's distribution system.

Complete the steps below (in order) to flush your building’s system:

1. If you have a building engineer or facility manager, consult with them to assist in flushing the internal plumbing.
2. Turn on the cold water inside the building (break room sinks, drinking fountains, utility closets, restrooms, etc.) on each floor.
   1. Start from the furthest point away from where water enters the building (e.g., for a building with five floors, start on the fifth floor and work your way to the first floor.) Remember to run only cold water.
   2. When the water temperature cools slightly, you have successfully flushed the water.
3. Flush hot water storage tanks (boiler or hot water tanks per manufacturer’s flushing instructions) to displace stagnant/discolored water with fresh water.
4. Repeat step 1 using hot water.
   1. When the water temperature turns hot, you have successfully flushed the water.
5. Flush and perform preventative maintenance on point-of-use devices or systems, such as cooling towers, systems providing additional water treatment, etc., per the manufacturer’s recommendations as applicable.

Once all domestic water service lines, internal plumbing, and point-of-use devices/systems are flushed/adequately maintained, it will be safe to drink the water.

Things to do after flushing your system:

• Notify your building occupants of the status of the water systems and the flushing program.
• Develop a water management program.
• Consult the CDC for comprehensive, industry-specific guidelines.

Additional Resources:

• CDC Guidance for Reopening Buildings After Prolonged Shutdown or Reduced Operation
• ASHRAE Guideline 12-2020 – Managing the Risk of Legionellosis Associated with Building Water Systems