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Do You Know Where Your Tap Water Comes From?

Lake Shasta, California's largest reservoir, supplies water to the Central Valley | Photo: Roger Wollstadt/Flickr/Creative Commons License

It's one of the questions posed by the new wave of environmentalists back in the late 1960s, as a way of gauging just how much you know about where you live: when you turn on the tap in your house, where did that water come from? Forty years later that question can still be a stumper -- especially in a place like Los Angeles, where the water in your tap may have come from the eastern Sierra, or Mount Shasta's slopes, or the Wind River range in Wyoming.

And if you don't know where your water comes from, how can you pay attention to things that might threaten the quality of that water?

Californians have altered the way the state's water flows on a massive scale. But even with our aqueducts and canals to move the water hundreds of miles, and even with our treatment plants to take some of the potential pollutants out of our water before we drink it, we're still almost completely dependent on natural water systems to provide us with water to drink and to irrigate our crops. We also depend on the geology and biology in those natural systems to keep our water free of the worst pollutants.

If we disrupt those systems, we run the risk of endangering our water supply, and its quality. So it makes sense that we ought to pay attention to what's happening in the watersheds from which we get our drinking water. A watershed is the total land area whose precipitation drains past a certain point. The San Francisco Bay watershed, for instance, includes most of the interior part of Northern California, from Alturas south to Fresno. It's the area in which any rain or snow that falls, if it doesn't evaporate or get sent out of the area in an aqueduct, will eventually flow downhill to the Bay.

Within each watershed there are natural systems that maintain water quality. Healthy soils will strip pollutants out of rain and snow. Vegetation slows erosion, keeping the water downstream more free of sediment. Porous landscapes release rain and snow a bit at a time, helping to keep rivers from alternately flooding and drying up.

And altering those systems -- cutting down forests, introducing industry, paving surfaces so that rain runs right off rather than soaking in -- can hurt the watershed's ability to keep your drinking water pure.

Finding out where your water comes from is important if you want to keep track of activities that might make that water a bit less clean. Some watersheds, like those that provide San Francisco with its drinking water, are small and mainly protected from any kind of development. Others, like two of the three that supply Los Angeles, contain pesticide-using farms, unprotected open land, and huge cities with millions of cars leaking motor oil into the storm drains. But finding out which watersheds serve you hasn't always been easy, much less finding out how much of those watersheds is protected.

A new online tool released today by The Nature Conservancy offers Californians a way to learn more about where their water comes from, and what kind of human activity it flows past on the way to the glass. Enter your ZIP code into the "Conserve California" tool's interactive map and -- if you're in one of the state's more populated areas -- up pops a set of color-coded layers on the map that show which watersheds your water comes from, which developed areas that water goes to, and the path the water takes along the way.

You'll also learn how far your water may have come to see you and the percentages of the watershed that are protected from development, undeveloped but unprotected, or developed.

In putting together the tool and its accompanying report (6.4 MB PDF), TNC found that:

California's drinking water supply system relies on approximately 157 million acres of land spanning 8 states to collect, filter, and deliver water. Only 16% of this land is strictly protected from development and degradation (e.g., wilderness areas, national parks). Roughly half of the land (51%) has some level of protection but designated for multiple uses including significant landscape-disturbing activities like logging, road building, and mining. The remaining 33% is in private ownership with highly variable levels of protection from development and degradation. In fact, 7.7 million acres (5%) of the watersheds supplying California's drinking water have been converted to agricultural uses and an additional 3.2 million acres (2%) has been converted to urban and suburban development.

Other states contribute water to California via the Colorado River, which drains parts of Wyoming, Colorado, Utah, new Mexico, Arizona and Nevada, and the Klamath River, which drains a small part of Oregon. Both of those rivers have been the focus of intense controversies over water allocations.

Los Angeles' watershed | Screen capture from Conserve California

Los Angeles, for its part relies on the most watershed land of any of California's cities for its H2O habit. About 146 million acres of watersheds feed L.A., an area half again as large as California. Almost all of the watersheds L.A. depends on are several hundred miles away from the city, or farther. Half of that land is protected from development and degradation, with another third protected from development but vulnerable to damage from activities such as grazing, resource extractions, or other abusive uses.

A bit unsurprisingly, San Francisco ranks as the city with the largest percentage of its watershed lands fully protected, mainly in the Yosemite high country but also including a handful of smaller protected watershed lands in the hills of the Bay Area. More than 80% of San Francisco's watershed lands enjoy the highest level of protection, with another 8% or so partially protected. Fresno has a higher percentage of watershed lands with some protection -- 89% -- but more of Fresno's watershed is on lands such as National Forests that aren't protected from impacts such as logging. Just over 50% of Fresno's watersheds are fully protected, mainly by way of Sequoia and Kings Canyon National Parks.

The tool covers the coastal and inland valley areas in which 80% of Californians live. A quick browse of smaller cities and towns shows that coverage in the outback is a bit spotty, and even some more prominent towns have escaped inclusion. There's no information listed as yet for Eureka, Barstow, or Truckee, for example. But for four fifths of us Californians, the Conserve California site offers a great way to bolster the water-related part of your own personal environmental education.

Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.

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