Can California further reduce urban water use?

Jay Lund, the Ray B. Krone Professor of Environmental Engineering, UC Davis
Ryan Cahill, graduate student, Department of Civil and Environmental Engineering, UC Davis
 

Reducing urban water use has become a major long-term policy goal.  In 2009, California adopted a policy of further reducing urban water use by 20 percent per capita by 2020.  Is this a reasonable goal?  Is this goal too lax or too stringent?

California has had some success in reducing per-capita urban water use in recent decades.  As early as the 1976-77 drought – the worst single dry year on record – Bay Area water utilities found that they could temporarily reduce water use by up to 40 percent without major civil or electoral unrest.

In the last 20 years, per capita urban water use in southern California has declined, so Los Angeles can boast that its total water consumption has not risen, despite substantial population growth.  Some of this conservation arises from the loss of water-consuming industries; industrial water use now accounts for only about six percent of urban use, compared to eight percent in 1990. However, much urban water conservation comes from reduced residential use, which is about 70 percent of all urban use. Reductions in urban use have mainly come from increased operation of water-conserving toilets and other household fixtures, smaller lawns, and less outdoor use by residential and commercial users.

How low can we go, in terms of urban residential water use?

Australian drought Wagga NSW December 2006 by John Schilling

Australia, with a similar economy and a comparable climate and culture, offers a reasonable scenario for reduced urban and residential water use.  Some lessons from comparing urban and residential water use in California and Australia are:

1. Although the reliability of urban water use data is often questionable, especially for California, it is clear that Australians use far less water than Californians (Figure 1).  In 2009, Australian residential use, on average, was almost half that of Californians—59 gallons per capita per day (gpcd) as compared to 105 gpcd in California. Not only does Australia have less per-capita residential use than California overall, but nearly every major city in Australia used less water per capita than metropolitan areas in the Western U.S. (Table 1). While California has reduced per-capita use by 10 percent from 2000-2009, Australian per-capita water use has fallen about 30 percent in the same period. The Australian numbers show that the 20 percent reduction goal in California is feasible, with room for additional urban conservation.

2. The biggest differences between Australian and Californian residential water use are outdoor water applications, toilet operation and leaks (Figure 1).  More than half of Australia’s lower residential water use is from lower outdoor water use, and more than two-thirds of the difference is accounted for by lower Australian water use outdoors and for toilets.

3. Although the prolonged Australian drought, which lasted for much of the past decade, motivated major reductions in urban water use, the largest reductions came from outdoor water use restrictions, programs to accelerate retrofitting of dual-flush toilets, and additional motivation to conserve, brought about by higher water prices.  However, because of the higher water rates, water utility revenues per residential connection are generally not lower than in California.

4. California could have lowered urban water use by 2.1 million acre-feet in 2009 if it had the same residential water use rates as Australia, and potentially saved 1.9 million acre-feet (maf) for consumptive use by others. (For inland areas, not all water use reduction saves water.)  For comparison, total urban use in California in 2005 was 8.3 maf, and total annual agricultural and urban water use is about 43 maf.

5. As in Australia, such conservation would not come without cost and inconvenience.  However, this change in water use in urban Australia, driven partly by drought and partly by longer-term conservation policies, is likely to pay dividends in terms of reducing water shortages for a long time to come.

Table 1: Water use in selected Australian and Western U.S. cities, 2005.

Figure 1: Californian and Australian residential end uses

 

Further Reading:

Cahill, R. and J.R. Lund, “Residential Water Conservation in Australia and California,” Journal of Water Resources Planning and Management, ASCE, Vol. 139, No. 1, Jan./Feb.,  pp. 117-121, 2013.

Cahill, R. and J.R. Lund (2011), “Residential Water Conservation in Australia,” working paper, Center for Watershed Sciences, University of California – Davis.

Hanak, E., J. Lund, A. Dinar, B. Gray, R. Howitt, J. Mount, P. Moyle, and B. Thompson (2011), Managing California’s Water:  From Conflict to Reconciliation, Public Policy Institute of California, San Francisco, CA, 500 pp.

Lund, J., Hanak, E., R. Howitt, A. Dinar, B. Gray, J. Mount, P. Moyle, and B. Thompson (2011), Taking Agricultural Water Conservation Seriously, Californiawaterblog.com

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