California Water Sustainability Cheat Sheet

Source: U.S. Department of the Interior Bureau of Reclamation, Mid-Pacific Region. Water Supply and Yield Study.

Water Supply and Demand

This graph shows the sources of California's yearly water supply on the left and follows the flow of that water to its final destinations on the right. Supply and demand is shown for an "average" year (the study considers 2000 to have been an average year). You can hover over the items to view the total amount of water for that flow in millions of acre-feet (MAF).

Perhaps the most important thing to note from this diagram is that the average yearly unsustainable overdraft (the "Unsustainable overdraft" source) from ground and surface water reserves is around 6.7 MAF (note that this is despite another 2.3 MAF of demand that is never met). To put this into perspective, the total amount of reserved water stored on the surface is 40.7 MAF and while the amount of reserved ground water is difficult to measure, it is costly and time-consuming to dig deeper wells.

Notice that urban use is around 11% of the total water demand. While this may not seem like a large amount, as California's population continues to increase, this (and to a lesser extent agricultural use) will become an increasingly larger component of water demand in the future.

Water supply → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → Water demand


If the study provided a range of values I used the average of the range in most cases. The exception was for the fraction of outflow from total supply (which is unpredictable to begin with) for which I used a value closer to the maximum of the range in order to make sure the water market cleared (supply and satisfied demand were similar).