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A Balancing Act For hydrologists, an important tool is a "water balance," a comparison of water supply to use. A water balance published by DWR in its 1993 update of the California Water Plan (Bulletin 160-93) shows the scales balanced in 1990 with statewide total net demand of 63.7 million acre-feet in an average water year equaled by supply. However, when DWR calculated a water balance under drought conditions, it came up with a 2.7 million acre-feet shortfall in supply for 1990. (One acre-foot of water is equal to about 326,000 gallons, enough to cover a 1-acre area with 1 foot of water and can meet average annual indoor and outdoor needs of one to two urban households). Assuming average precipitation conditions - even with conservation measures in place - DWR is pro- jecting a gap in the year 2000 ranging from 3 million aere- feet to 5 million aer€- feet between water supply and demand. The gap steadily wid- ens as DWR projects out to the year 2020. The ligures are even more alarming when drought condillons are assumed. DWR is projecting annual shortages ranging up to 9 million acr8- feet by 2020 under drought conditions. PROIECTEP WATER SHORTAGES 1.'itl:l''''.tlll.JI1Ulli,l._ 70 1990 2000 2010 2020 YEAR I..~._ 0.... .~... __'b3-5 635 653-67.3 659-679 667~.7 SUPPLY I SHORTAGE DEMAND ~5 ~3 ~7 ~o 111:ll]llr1:..'I.IIIIIIIIIIII.._ 70 j 65 . ~&o 1990 2000 '2-<2 3.7-5.7 2010 2020 YEAR In the past. the tradi- tional way of closing the gap between supply and demand has been to increase supplies - either by building new facilities such as dams and pumps or by tapping underground aqui. fers. But building new facilities is costly and such projects face strict environmental review before they can be approved. Groundwater resources. although abundant in many areas of California, are overdrafted in others and take time to replenish. And overpumping ground- water can lead to subsidence, an often irreversible collapse of the earth's surface overlying an aquifer, or saltwater intrusion into coastal aquifers. Conser- vation is an option that can cost-effectively stretch 532 549-56.9 55fH15 563-583 DEMAND 2.7 6-6 50.5 48.9 49.1 49.3 7-9 /:,'\'e/1 with COf/serration measures in place, the stale Department ~rWater I?esol/rces water !Jalol1ce for the .Iitlllre shows a large gap betwcen supply and demllnd - especially in drought years. 4 SUPPLY I SHORTAGE 6.4-8,4 uses of available water and help preserve ground- water resources. The California Water Plan estimated in 1993 that a combination of urban and agricultural demand- management programs. land fallowing. water banking and voluntary rationing during droughts. and permanent land retirement in areas with poor drainage could reduce net water demand by a total of 3 million acre-feet by 2020. Water uses fall into three main categories: agricul- tural, urban and environmental. Agricultural uses are mainly irrigation water to support the state's vast farming industry, which includes the production of nursery plants. Urban uses include domestic water for urban residents, landscaping and parks, and for governmental, industrial and commercial facilities. Environmental uses primarily are maintenance of adequate flows in rivers and streams to preserve habitat for fish and wildlife. California's vast water-supply system produces an average of about 36.5 million acre-feet of water per year from reservoirs and aqueducts, groundwater wells, or diversions from streams and rivers, accord. ing fo DWR figures. This water supply often is referred to as "developed water," water captured behind dams, in reservoirs or pumped from the ground for human use. Agriculture uses about 80 percent of the developed surface water supplies in California. Agriculture's water usage is expected to drop slightly in the future, but water allocations to protect fish and wildlife habitat and a growing urban population are contributing 10 pressure to improve the efficiency of water use everywhere. California's population continues to grow, contribut- ing to the projected gap between water supply and demand. California's population totaled 32.6 million in mid-1995, with annual state population growth averaging about 2 percent per year during the preceding 20 years. The state Department of Finance projects California's population will reach 49 million by the year 2020. Population growth has fueled strong competition belween urban and agricultural water users. Although water planners project that agricultural water demand will decline slightly, that demand is hardening because farmers are growing more permanent crops such as orchards. Urban water