Urban Water Use Efficiency

urban-water-use-sliderboxWhile California has accomplished much in reducing urban water use, opportunities still exist to reduce potable water demand by more than 2 million acre-feet

Toolbox Main Page IconCalifornia’s annual precipitation is more variable than in any other state in the nation; it can range from massive floods to deep droughts and everything in between.  In any given year, it is the presence or absence of just a handful of large storms passing through in the winter months that determines the fate of the state’s available water supplies.  Additionally, most of the state’s population and farms are located far from where the water falls.  This means that balancing water supply and demand has become a continuous problem.

Reducing demand is oftentimes the quickest way to respond to a water supply shortage, such as drought.  When demand for water outstrips supplies, water suppliers can either increase supplies, reduce demand, or a combination of both.  Increasing supplies is generally expensive as it includes costs to purchase water as well as the additional infrastructure to treat and convey that water.  In addition, infrastructure projects that increase water supplies generally take a long time to plan and build, and are therefore not effective as a drought response.  Reducing demand through increased conservation and efficiency is generally lowest cost and is quickest to implement.

There was a time not so long ago when water conservation was thought of as a temporary strategy used only to respond to drought; however, increasing population and growing demand have made water conservation and water use efficiency an important part of California’s water management strategy – so important that making conservation a California way of life is one of the tenets of Governor Brown’s California Water Action Plan.


Although the terms ‘water conservation’ and ‘water efficiency’ are often used interchangeably, they actually mean different things.  While both conservation and efficiency achieve the same goal of using less water, the difference is in the approach.  Water conservation can be defined as a reduction in water loss, waste, or use; water efficiency is defined as the minimization of the amount of water used to accomplish a function or task.  For example, only doing full loads of laundry rather than smaller loads would be an example of water conservation; using a water-efficient washing machine is an example of water efficiency.  Water efficiency is considered easier and often more sustainable than water conservation.


The total volume of urban water use statewide as report in the 2009 California Water Plan is 8.8 MAF per year, which is about 10% of the state’s supplies.  Of that, 65% is for residential use.

fig-3-1-average-baseline-water-useWater use widely varies regionally due to the state’s diverse geography and climate.  Generally, water use is lower along the coast and increases further inland.  The lower water use on the coast is generally due to the cooler marine climate and the smaller lot sizes typical of the coastal region; inland areas tend to use more water because they are hotter and drier and the residential lots are a lot larger.

Most urban use occurs in the San Francisco Bay and Southern California regions; both of these regions rely heavily on imported water.  However, despite growing population, substantial efforts in pricing incentives and installation of water-saving fixtures such as toilets and showerheads have led to significant reductions in water use.  Other contributing factors include increased public outreach efforts, plumbing codes, water efficient landscape ordinances, advances in irrigation technologies, and new technologies in the commercial, institutional, and industrial sectors.


In 2009, the Legislature passed the Water Conservation Act, which required all water suppliers to increase water use efficiency.  The legislation set a goal of reducing per capita urban water use by 20% by December 31, 2020.  The Department of Water Resources estimates that meeting this goal will result in a reduction of just over 2 million acre-feet of urban water use.

Water suppliers are fundamental to meeting the goal of the 20 x 2020 plan.  The legislation does not require a reduction of total water use in the urban sector, because changes in economics or population can affect water use. Instead, the legislation requires a reduction in per-capita water consumption.

Each urban water supplier is required to set water use targets based on historical water use, the local climate, and locally implemented conservation programs.  According to the Urban Water Management Plan’s that were submitted to the Department of Water Resources in 2010, the average water use target for 2020 was 166 gallons per capita per day.

Suppliers are expected to be halfway between the baseline and the 2020 target by 2015.  After receiving the 2015 UWMPs, DWR is directed to report to the Legislature on the progress made, and make recommendations if the state, overall, is not on track to meet the 20% target.


While much has already been achieved, tighter environmental restraints, population growth, and climate change means that even greater efficiencies in the future will be necessary.  The good news is that these additional savings in the urban sector are achievable.

table-3-4-projected-savings-by-sectorOutdoor residential use can potentially be reduced by 20 to 45% by actions such as changing to drought-tolerant or lower water use landscapes and installing more efficient irrigation systems.  Further efficiencies can be achieved inside the home by replacing older, inefficient fixtures and appliances with newer, water efficient equivalents.  The commercial, industrial, and industrial sectors could potentially save another 10% by using recycled water or by reusing process water.  Steps can be taken to reduce water losses within water distribution systems to achieve greater efficiencies.

By combining the estimated demand reductions in the urban water use sector, the California Water Plan notes that California reduce the demand for potable water in the year 2020 by more than 2 million acre-feet; alternative water supplies such as recycled water, desalinated water, grey water, and rainwater are expected to further reduce statewide demand.


table-3-5-sample-cost-of-water-use-efficiency-measuresThere are many benefits to increasing urban water use efficiency, such as increased reliability of water supplies, increased capacity to meet growing demands due to population growth, delayed capital costs for new infrastructure to treat and deliver water, reduced volume of wastewater which reduces capital costs and ongoing treatment costs, increased availability of water for surface or groundwater storage, and reduced water-related energy demands and associated GHG emissions.

Water conservation and water use efficiency are also considered primary climate change adaptation strategies that should be undertaken first because they are generally lower-cost and provide multiple benefits.  By implementing practices that reduce waste and increase efficiency, the urban water use sector will be better equipped to adapt to potential reductions in water supply.

water-use-efficiency-coverIt is conservatively estimated that a well-implemented set of water conservation programs would cost a water supplier an average of $333-$500 per acre-foot.  However, not all water conservation programs can be quantified in terms of cost per acre-foot but are nonetheless a valuable part of a water use efficiency strategy; these include hiring a water conservation coordinator, implementing education and outreach programs, using water conservation rate structures, and developing and implementing a water waste prohibition ordinance.

Click here to download this resource management strategy from the California Water Plan.


Reports on urban water conservation and efficiency …

  • The 20 x 2020 Water Conservation Plan: The 20×2020 Water Conservation Plan is a statewide road map developed by state agencies to maximize the California’s urban water efficiency and conservation opportunities between 2009 and 2020 to achieve the 20 percent per capita reduction in urban water demand by 2020.
  • Waste Not, Want Not: The Potential for Urban Water Conservation in California: A report on urban water use in California released by the Pacific Institute of Oakland, California.
  • Lawns and Water Demand in California: This report from the Public Policy Institute of California analyzes population growth and housing trends in the state’s major climactic regions, estimate residential lot and yard sizes, and examine the water needs of cool-season turf grass lawns. They also evaluate several outdoor water conservation programs.

Fact sheets and briefs on urban water use, conservation, and efficiency …

Helpful websites on urban water conservation and efficiency …

More on urban water conservation and water use efficiency from Maven’s Notebook …

View all posts on urban water conservation by clicking here

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