The Reflecting Pool is generally drained for cleaning over the winter. The water flows either into the Tidal Basin or into the city’s water system.

jmilb / Flickr

Here’s a fun fact about Washington: The Lincoln Memorial Reflecting Pool contains 4 million gallons of water when filled. Another fun fact: It takes between three to four days to drain all that water for regular cleaning and repairs to the pool. Such drainage is happening this week, the National Park Service tweeted Wednesday.

But where does the H20 go when drained from the pool? It flows either into the Tidal Basin or the city’s water system, according to NPS spokesperson Mike Litterst. The water is going to the latter in the current case, says Litterst, adding that workers filter the water through the pool’s pump house as the water exits via pipes.

“We go slowly because we don’t want to overwhelm the city with 4 million gallons of water in a day,” Litterst says. The Park Service received permits from the District government to discharge the water from the pool into the city’s water system.

It will take about a month for the maintenance work to be done and the Reflecting Pool to be refilled. If the cherry blossoms bloom particularly early, it’s possible that the pool could still be sitting empty during that otherwise picturesque period. 

Refilling the basin takes roughly three to four days as well, or potentially even a bit longer, says Litterst. Pipes pull new water from the city’s system into the pool.

The cleaning and repairs usually take place every winter, but they also sometimes occur later in the year if the water in the Reflecting Pool is having quality issues. Last May, for example, a broken water line reduced the circulation in the pool, resulting in a algae growth on the surface of the water. And in 2017, a snail-carried parasite killed about 80 ducklings in the pool. (More than 50 were found dead in just two days.)

This isn’t the only body of water on the National Mall that NPS occasionally drains and cleans, according to Litterst. The pond in Constitution Gardens needs periodic maintenance too, except it lacks a drainage system that connects to the city’s water system like the Reflecting Pool has. “We literally have to run hoses into there,” Litterst says of the Constitution Gardens pond. But since the pond is smaller, it doesn’t require an annual cleaning.

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