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california Water Today 87 Although DWR has made greater efforts in recent years to quantify and document gross and net water use by sector in different parts of California, these efforts are hampered by a lack of local reporting of water use. Estimating gross use is less difficult where water deliveries are quantified for billing purposes—e.g., surface water deliveries to contractors of the CVP and SWP and metered household water deliveries. But measurement is problematic for self-supplied surface water and groundwater, which have few if any reporting requirements. As a result, DWR must essentially back out estimates of agricul- tural groundwater use from crop production estimates, themselves imprecise. Net water use is even more approximately estimated.7 Water use reporting is a highly charged issue, and water users—particularly agricultural users—have successfully resisted legislative efforts to strengthen reporting requirements for groundwater withdrawals and stream diversions. Yet without better report- ing, California’s water accounting and water rights enforcement will remain approximate at best—an increasingly difficult handicap for policy discussions and water management in a water-scarce state. How Much Water for the Environment? Environmental water use and demand estimation is particularly difficult and controversial (Null 2008; Fleenor et al. 2010). Since the late 1990s, the state’s Department of Water Resources has published water use estimates that explicitly show dedicated environmental flows as a share of total water use.8 Environmental water use estimates include flows in designated Wild and Scenic Rivers, required Delta outflows, and managed wetlands. Based on data such as those presented in Table 2.2, it has become common for some observers to argue that the environment receives the lion’s share of water supplies (implying that it should not receive more).9 Indeed, statewide, environmental flows accounted for nearly 50 percent of both gross and net water use in the 1998–2005 period and about 40 percent for agriculture and 10 percent for the urban sector. 7. For example, net urban use should be significantly higher in the coastal areas because treated wastewater generally flows to the sea. In inland areas, return flows from water users go to rivers and are available for reuse downstream. Oddly, the ratios of net to gross use from DWR water use estimates do not reflect the expected pattern—inland regions such as the Sacramento and Colorado Rivers have higher ratios of net to gross water use than the Central Coast. 8. This practice began with the publication of Bulletin 132-98, the first to consider the environmental share of water as a portion of the total (California Department of Water Resources 1998). 9. As an example, this comment by Tom Birmingham, General Manager of Westlands Water District, in the October 24, 2009, edition of The Economist: “Westlands’ Mr Birmingham says that, in practice, water usage has already become equal. Whereas agriculture used to consume 80% of the state’s water supply, today 46% of captured and stored water goes to environmental purposes, such as rebuilding wetlands. Meanwhile 43% goes to farming and 11% to municipal use.”