Voters just approved $7.5 billion dollars for new water storage projects, but a new study says it's likely not all projects will be worth the money.
The study says there is a limited amount of water that could be stored by future dam or reservoir projects in California because there is a limited amount of rain and snow runoff that can be captured.
The study suggests California could create storage for no-more-than six million acre-feet in combined additional surface and groundwater facilities. That's equivalent to the 15-percent of water not captured annually.
Jay Lund is the Director of Watershed Sciences at U-C Davis and co-author of the study.
"For water storage to be useful, you have to be able to do two things. You have to be able to fill that storage and then you have to be able to move that stored water somewhere where there's water demand."
The authors say for storage projects to be effective, they must be part of a statewide conveyance system. The study suggests the costs could be prohibitive.
Lund says plans to build new reservoirs must also consider the cost of moving the water versus the return on investment.
"You build all the utilizable capacity and you build this conveyance through the Delta that lets you make use of it all, we're looking at less than a five percent increase in water deliveries statewide."
There is 42 million acre feet of capacity in 1400 reservoirs.
The study says California now fails to capture six million acre feet of rain and snow runoff. That's equivalent to about six Folsom Lakes.