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Building Flushing Questions Answered

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Non-Residential Flushing Questions

Flushing means running the tap water long enough to completely replace old, stagnant water in the pipes with fresh water. Stagnant water can cause/lead to many water quality problems, such as loss of chlorine residual, bacterial growth, elevated lead levels, and discolored water. If this happens, it is important to perform flushing before using any water.

Any homeowner or business that has left their property unoccupied or unused for an extended period of time should flush their pipes when they return to the building and before they start consuming the water. If you have been staying home or using the water normally, you do not need to flush.

A long period of water stagnation leads to loss of disinfectant residual in the water, which means the water is no longer protected from bacterial growth. Harmful bacteria, such as those that cause Legionnaires’ disease, can accumulate in the absence of chlorine. Water chemistry changes in the stagnant water and long contact time with lead sources may lead to an increased level of lead in the water. This water can become unsafe to drink or use for residential or commercial purposes. Additionally, stagnant water can become discolored over time as rust debris break off from corroding iron pipes.

Before you start flushing procedures as outlined here check plumbing devices such as backflow preventers or sprinkler systems to make sure they are operational and there is no leak in the building plumbing system. You may also close the valves separating outside spigots or irrigation systems, as sudden water flow in these pipes can cause infiltration of contaminants from outside. In larger buildings, check HVAC systems, because they can become the source of Legionella, a harmful bacterium.

WSSC Water continues to conduct thorough and uninterrupted water quality monitoring throughout our service area and has not seen any indication that the quality of the water supplied to your property has been compromised.

WSSC Water uses free chlorine as a primary disinfectant to safeguard against microbial contamination. Chlorine residual of 0.1 mg/L is considered minimally effective in controlling bacteria. During the past several months, we have maintained about 1 mg/L or higher chlorine residuals throughout the distribution system. However, chlorine can dissipate if the water remains in the building plumbing for a long time, losing its ability to prevent contamination.

WSSC Water is providing recommendations for homes and business. We can help answer questions or provide more detailed information about water quality in your area.

If you need additional clarification on the flushing recommendations or have general water quality questions, please call 301-206-4002 or email Our water quality staff will respond within 48 hours.

If you experience discolored water or other water quality problems that will not go away after flushing, please call our 24/7 Emergency Service Center at 301-206-4002.

Last Modified: January 27, 2021, 1:16 pm EST