Back in 2016, after repeated problems with “brown water” in multiple West Seattle neighborhoods, Seattle Public Utilities carried out a major flush of local lines. Now they’re planning one for southeast West Seattle and South Park, in the areas outlined on this map:

That map is included in a letter SPU has just mailed to affected residents and businesses, saying the flush will start soon and continue into next year. Here’s what else the letter says:

SPU is performing this work to help maintain water quality and help reduce the occurrence of discolored water that can sometimes occur. Flushing won’t eliminate discolored water, but it will help decrease it.

What do customers need to do? SPU crews will perform the flushing at night by flowing water from fire hydrants. Residents and businesses do not need to take any action to prepare for this work. Customers will be able to use their water as usual. When crews are flushing nearby, customers may notice a slight reduction in their water pressure. They may also experience temporary discolored water, which should clear quickly once crews are done flushing the water main. Running the cold water for a few minutes can also help clear the discoloration.

Why does discolored water occur? Discolored water can happen when crews operate a fire hydrant, when there is a water main break or leak, or when the water in the pipes is forced to travel in a different direction than normal. When one of these events happens, sediment in the water and rust in the pipes get stirred up, causing the water to look discolored. Flushing the water mains will remove some of the sediment and rust that has been resting in the pipes. This will help reduce the level of discoloration and the time it takes for the water to clear when there’s a disturbance in the pipes.

Is the water safe? Yes. Every single day, SPU takes samples throughout the drinking water system that serves 1.5 million people. The water is tested for contaminants and is regulated by the Washington State Department of Health. Seattle’s water remains safe to drink.

See the full letter here.