WATER ENERGY USE IN CALIFORNIA

Water use in California consumes significant amounts of electrical energy. Preliminary estimates indicate that total energy used to pump and treat this water exceeds 15,000 GWh per year, or at least 6.5 percent of the total electricity used in the State per year. This energy use is expected to increase due to a growing population, increasing reuse of wastewater, the remoteness or lower quality of alternative water sources, and increasingly stringent treatment requirements due to a variety of water quality and environmental protection concerns.

Water use results in such large energy costs primarily because so much of the State's water demand is located far from available sources, and the moving of water is inherently energy intensive. An acre-foot of water, the volume of water which would cover an acre of land to a depth of one foot--enough water to serve a family of five for a year--weighs approximately 1,400 tons. In total, California uses about 42.6 million acre-feet of water per year for agricultural, municipal, and industrial purposes, weighing some 550 million tons. Significant amounts of energy are also involved in other areas of water use, including water treatment, reclamation, and desalination.

The State Water Project, which moves large quantities of water great distances and over steep terrain, is the largest single user of electrical energy in the State. It accounts for 2 to 3 percent of all the electricity consumed in California. The SWP uses an average of 5,000 GWh per year.

Here "water used" means water used for agricultural and urban purposes. It does not, therefore, include the 37 million acre-feet of water annually committed to remain in rivers and lakes for environmental purposes. Also, unless otherwise indicated, figures given for annual water and energy use are for average years.

Imported Water Supplies

In California, there are eight large water projects that take water from one region and transport it for use in a different region: the State Water Project (SWP), the federal Central Valley Project (CVP), the Los Angeles Aqueduct, the Hetch-Hetchy Aqueduct, the Mokelumne Aqueduct, the Colorado River Aqueduct, the All-American Canal and the Coachella Canal. The SWP, CVP and the three Colorado River projects deliver over 15.3 million acre-feet of water per year. The State and federal projects in particular require substantial pumping to transport water from the Sacramento Valley to the Central Valley, the San Francisco Bay Area, and Southern California. The lift of SWP water to the top of the Tehachapi's for delivery to Southern California is the largest of these pumping efforts and requires over 2,200 kWh per acre-foot of water pumped.

Reservoirs also generate electrical energy, and water projects are most often net producers of electrical energy. The net energy demands of surface water suppliers vary from project to project. For the SWP, energy demand also varies from customer to customer. For example, SWP water delivered to Bakersfield in the Kern County Agency requires a net energy input of 366 kWh/acre-foot; for water delivered to Los Angeles (at Castaic Lake Reservoir), a net of 1,666 kWh/acre-foot; and for water delivered to the San Bernardino Valley Municipal Water District, a net of 3,824 kWh/acre-foot.

The current trend is for increasingly energy intensive water projects to store excess water in wet years, since most of the accessible water sources have already been developed. For example, the Metropolitan Water District of Southern California is constructing the East Side Reservoir in Riverside County. This 800,000 acre-foot reservoir is larger than all current Southern California reservoirs combined, has been constructed in a valley with no natural water source, and will take at least four years to fill with water pumped from the Colorado River and northern California.

Groundwater

Groundwater contributes approximately 30 percent of the water used in California, or about 14.0 million acre-feet per year. (This figure includes about 1.5 million acre-feet per year of groundwater overdraft. "Overdraft" is where pumping exceeds the replenishment of the aquifer.) Agriculture uses the greater part of the groundwater used statewide. Generally groundwater must be pumped to be put to use, requiring energy to lift it to the surface. Most groundwater is used locally in the area overlying the aquifer from which it is drawn.

The amount of energy used in pumping groundwater is unknown due to the lack of complete information on well-depth and groundwater use. DWR has estimated groundwater use and average well depths in three areas responsible for almost two-thirds of the groundwater used in the State: the Tulare Lake basin, the San Joaquin River basin, and the Central Coast region. Based on these estimates, energy used for groundwater pumping in these areas would average 2,250 GWh per year at a 70 percent pumping efficiency (1.46 kWh/acre-foot/foot of lift). In the Tulare Lake area, with an average well depth of 120 feet, pumping would require 175 kWh per acre-foot of water. In the San Joaquin River and Central Coast areas, with average well depths of 200 feet, pumping would require 292 kWh per acre-foot of water.

Sources of Alternative Water Supplies - DWR anticipates that the demand for water will continue to exceed the supply of developed sources for at least the next twenty-five years. Since traditional water development (i.e., dams) is both expensive and controversial, there is much interest in new sources of water. Two in particular are reclamation and desalination. Development of these sources has been limited because of their cost. A significant factor in the cost of reclamation and desalination is their intensive energy requirements. Therefore, they are likely candidates for energy efficiency improvements.

• Water Reclamation - Treated municipal effluent may be made available for other uses. Generally, reclaimed water may be used for municipal purposes that do not involve human contact or consumption, such as residential landscape irrigation, golf course watering, and industrial cooling water. Depending on the intended re-use, this water usually requires more extensive and energy intensive treatment than does wastewater that is discharged to the environment. Reclaimed water is increasingly being considered for reuse for domestic water consumption. At this time, water quality standards and caution require complete retreatment of the wastewater. This is being done in two ways: feeding the treated wastewater back through a water treatment plant; and recharging groundwater aquifers, which naturally purifies the water and also subjects it to treatment and disinfection when it is withdrawn. This extra pumping and "double-treatment" results in significantly higher energy requirements than for traditional water sources.
• Desalination - Desalting brackish groundwater, as well as some surface water, agricultural and municipal wastewater, and seawater is the other emerging source of new water in the State. DWR expects that over the next twenty years it will not account for much more than a few tenths of a percent of all the water used in California. The primary desalination technology in use today is reverse osmosis, accounting for 90 percent of the water desalted in California. Reverse osmosis filters salty water under pressure through a semi-permeable membrane, leaving the salts behind. Currently, energy constitutes about 50 percent of the costs of reverse osmosis desalination, and energy costs alone can exceed $1,000/acre-foot. By comparison, it costs the Metropolitan Water District of Southern California an average of $115-$135 for one acre-foot of treated SWP water. There are numerous research efforts underway to develop more effective and less costly desalination methods. Recent developments in low-pressure membranes show promise for reducing energy requirements of desalination, and significant opportunities remain for further technology improvements.

Agricultural Use

Agricultural water use in the State constitutes 80 percent of all water used in California, or about 33.8 million acre-feet per year. Once water has been delivered to a field, whether by being pumped from the ground or pumped from a stream or canal, "furrow" and flood irrigation, the most common irrigation methods, rely on gravity to distribute the water over the field. Increasingly, farmers are using water-conserving pressurized pipe systems, such as sprinklers or low volume systems. These require pumps and extra energy to supply the pressure these systems require. Today, 87 percent of these pumps are electric.

Agriculture uses about 21.8 million acre-feet of surface water and 12 million acre-feet of groundwater per year and it is generally not treated before it is used. Treated municipal wastewater is, however, a source of agricultural water supply, with about one-third of the water reclaimed in California used for agricultural purposes (155,000 acre-feet). In 1995, agriculture used approximately 4,400 GWh of electricity for pumping and irrigation purposes.

Urban Use

Urban water use constitutes about 20 percent of the water used in California, or 8.8 million acre-feet per year. Water delivered to a municipal water supplier has two additional energy requirements before it can become available to the customer: treatment and pressurization. Water delivered through municipal systems generally must be pressurized, using pumps to store water in aboveground tanks or to pressurize water mains directly for distribution and for water pressure for the customer.

About 6.7 million acre-feet of surface water and 2.1 million acre-feet of groundwater are used in urban areas per year. In 1995, non-residential urban water suppliers consumed approximately 8,600 GWh of electricity, not including those industries having their own water supply and the energy requirements for water use in industrial processes.

• Water Treatment - Municipal water treatment can involve several processes to make water suitable for human consumption. These include aeration (for taste and odor), sedimentation, filtration, and chlorination or other forms of disinfection. The primary use of electricity in the treatment process is for pumping water through the treatment process and to storage before use by the customer. New treatment processes to meet emerging health concerns, such as ultraviolet radiation and ozonation, are also high energy consumers.
• Residential and Commercial Use - Residential and commercial uses are extremely similar. Residential uses include drinking, cooking, washing, bathing, and landscape maintenance. Commercial activities also include many of these same uses, either as amenities for personnel or, for example in the case of hotels and restaurants or cleaning services, as part of the product and services they provide. Most of the water used in this sector is for landscape irrigation. Additional energy requirements for residential and commercial water use are for heating water for cleaning, cooking, bathing, and laundry, which largely uses natural gas rather than electricity.
• Industrial Use - Industrial users may receive their water from municipal water suppliers, or they may have their own sources of water. Industrial use may have water treatment requirements different from other urban uses of water, usually to protect against corrosion and mineralization of plant fixtures and equipment. There are three general ways in which water is used in industry: for machine or product cooling water; for process water (i.e., water that is used in the production process, such as in the food and beverage industries and the paper products industries); and for boiler feed for steam energy and electrical generation. Cooling is the largest use of water in industry and its main energy requirement is for pumping to circulate the water.

Future Water Demand and Use
DWR indicates that water use in California is expected to grow by less than 1% over the next twenty-five years. At the same time, population is expected to increase from 32.1to 47.5 million people by the year 2020. DWR, however, expects water shortages to decrease over the next 25 years, due to increased reclamation and desalination, transfers, and some surface water and groundwater development. DWR forecasts demand reduction in both agriculture and the urban sector, as well as a net shift of about 4 million acre-feet from agricultural to urban use. In part, this will be brought about by a shift to less water-intensive crops; and by a reduction in irrigated lands of about 325,000 acres due to urban encroachment and drainage problems.

A significant element in projected increased supplies is reclamation and desalination, of about 450,000 to 600,000 thousand acre-feet per year. This is compared to an estimated total water supply shortfall of 200,000 acre-feet in a normal year. Although they will remain a small portion of total water use even by 2020, new reclamation and desalination efforts are expected to play a relatively large role in minimizing California's expected water imbalance. And with increased utilization of reclamation and desalination will come increased energy use.

Urban water suppliers are moving in the direction of energy-intensive and costly alternatives to conventional methods of disinfection, such as ozonation and ultraviolet radiation, for health and safety reasons. The Environmental Protection Agency is imposing new and more stringent regulatory standards under the federal Safe Drinking Water Act for suspected carcinogens and other health risks caused by disinfection with chlorine. In addition, most conventional disinfection is ineffective against the pathogens Giardia and Cryptosporidium found in some surface water supplies. Finally, the use of chlorine poses environmental and human safety risks in storage and handling. The addition of these treatment technologies can increase energy consumption at a typical water treatment plant by 10-20 percent, and some plants may face even greater increases in energy use.

( Nur Haniza Zainal ", )