City Cast

Portland's Water Comes From a Rain Forest

Rachel Monahan
Posted on November 13
river with snow-capped Mt. Hood in the background, Oregon

The Bull Run Watershed. (City of Portland / YouTube)

Clean and plentiful tap water is one of those creature comforts we usually never think about. But where does Portland’s water come from?

For the city and surrounding communities, the main answer is a specially designated watershed, created by federal law in 1904.

Bull Run Watershed

Just 26 miles east of downtown are 102 square miles of temperate rainforest — the source of most of Portland’s water. That’s an area that’s nearly three-quarters the size of the city itself. There’s roughly 130 inches of precipitation per year — an extraordinary total, particularly given that it’s double to quadruple what various parts of our rainy city get. The water is guided from streams into reservoirs by two dams. To make it suitable for drinking, it’s treated with chlorine first, then with sodium carbonate and carbon dioxide. Gravity helps move the water through the pipes to Portland.


In the event of forest fires or other contamination, Portland has a secondary source of water: the Columbia South Shore Well Field, out along the Columbia River east of the airport. There are 20 wells out there, and unlike elsewhere in the country, they have not depleted.

The city usually relies on groundwater for roughly a month per year. In late August, for example, tap water included a mix of groundwater and Bill Run water after a hot dry summer had lowered water levels.

There are those who say they can detect a more bitter taste when tap water includes this source.

Index of Portland Water Stats

Here are some numbers that explain the scale of our infrastructure:

  • Chicago to Portland: that’s roughly the distance of the system’s pipes if laid end-to-end. It’s 2,250 miles.
  • 144 Olympic pools: That’s how much water is supplied each day. It’s 95 million gallons.
  • In total, that’s about 30 billion gallons of water each year for about a million people in Portland and surrounding areas.
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