Do you know where your water comes from?

If you live in Corvallis, about 70 percent of what you drink, bathe in and water your lawn with comes from the Willamette River.

That shouldn't be surprising, given that the Willamette is the main watercourse draining all of western Oregon between the Cascades and the Coast Range.

But think about this: Wilsonville just built a $50 million treatment plant on the Willamette. And dozens of cities, large and small, get their water from the McKenzie, the Santiam, the Tualatin and other Willamette tributaries.

That's apparent from a quick study of a new map produced by the Corvallis Environmental Center with funding from the Institute for Water and Watersheds at Oregon State University.

"As the area grows, more and more communities are looking into tapping into the Willamette River for their water supply," said Todd Jarvis, associate director of the Institute for Water and Watersheds.

The question is, will there be enough water to go around?

But that's not the only question the map's creators want you to ponder.

In addition to noting the location of every major water treatment plant in the Willamette Basin, the Willamette River Water Quality Map shows other key features such as dams, sewage treatment plants, landfills and major sources of pollution.

Insets chart the presence of mercury, pesticides, fecal bacteria and other contaminants; dissolved oxygen and temperature levels; and the extent of impermeable surface area in the basin. On the back is a wealth of detail about the various factors that impact the watershed's health.

"This is kind of a visually rich version of data that's already available," said David Zahler, a past president of the Corvallis Environmental Center board and one of the map's designers.

The idea behind the map was "to illustrate the connectivity between all our communities here in the watershed," Zahler said. "We want people to know their place, have a sense of place, and the watershed is an obvious thing that ties us all together."

Jarvis hopes to extend the mapping program to other watersheds around the state. So far he's received expressions of interest from community volunteers in the Deschutes and Umatilla basins.

Copies of the Willamette River Water Quality Map can be purchased for $10 at the OSU Bookstore, Grass Roots Books & Music, Peak Sports and other local businesses.

Bennett Hall can be reached at 758-9529 or bennett.hall@lee.net.