What percentage of California’s water comes from the Delta?

While calling for smarter use of the water we have (a subject short-changed by the water bond), we need to keep pointing out the flawed implication in DWR’s oft-reported statement that two-third of Californians are served by water from the Delta.

The suggestion, always, is that the well-being of a large percentage of Californians depends on fixing this fragile region we call the Delta.

Really, how many Californians rely on water from the Delta?

There are lots of questions here, including what constitutes reliance on water from a particular source. If you rely on that source, how much do you “need”? Enough to drink? That plus enough to flush your toilet, shower, and run your garbage disposal? All those plus enough to wash your car and keep your lawn green in August?

Also, do you get all of your water from one water source? For example, some people in the Bay Area get their water almost exclusively from the Delta, while others get part of their water from some other source, such as Hetch Hetchy.

DWR is the source of the statement that water from the Delta serves more than 25 million people. But other information from DWR suggests that the State’s reliance on water from the Delta is not as high as this figure implies.

Steve Evans of Friends of the River has done an estimate using a bar graph from the 2005 California Water Plan. This bar graph shows California Dedicated Water Supplies for Water Years 1998, 2000, 2001 and lists supplies in six categories: Local Projects, Colorado Project, Federal Projects, State Project, Ground Water, Reuse & Recycle, and Instream Environment.

First, Steve averaged each category. Then he added the Federal Projects and State Project columns, getting a total of 9.3 MAF from those two sources of supply.

Finally, he divided 9.3 MAF by the total amount from all six categories, 80.4 MAF. That produced a percentage of 11.56%.

So based on DWR’s own bar chart, the Federal and State water projects supply less than 12% of the water from all sources.

Steve notes that quite a bit of federal water is diverted and used by contractors before it even gets to the Delta, so the actual amount exported from the Delta is less than this calculated percentage.

Deirdre Des Jardins suggests another way of doing this calculation. She takes the total Agricultural and Urban Water Use in California in 2000 (which was 43.1 MAF according to the Pacific Institute) and divides that into Delta exports that year (a bit over 6 MAF according to DWR). This produces a figure of about 17.5%. That was in an average (rather than a dry or wet) year.

So statewide, it looks like at most 17.5% of the water Californians use comes from the Delta.

In July of 2009, there were just under 37 million of us. If some imaginary subset of Californians used only water from the Delta, and they used all the Delta exports, we would be talking about at most 6.5 million people.

Let’s get back to reality here. Let’s stipulate that two-thirds of Californians (as many as 24 million people) probably do rely to some extent on Delta water. But overall, water from the Delta provides less that 20%, and perhaps as little as 10%, of the state’s overall water supply.

If we ended exports tomorrow, we wouldn’t have two out of three Californians dying of thirst.

Restore the Delta will keep taking apart conventional wisdom this way over the next two years while the water bond lingers on life support. And we will keep telling the story of the Delta, a place of ecological, economic, cultural and historical importance, that is under attack by those promoting California’s unsustainable 20th century water policies.

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