Water in the U.S. is a huge energy user. Approximately 4 perecent of all electricity consumed in the U.S. is used to deliver water and treat wastewater, more than is consumed by the pulp, paper, and petroleum industries. In California water related energy use consumes 19 percent of the state's electricity, 30 percent of its natural gas, and 88 billion gallons of diesel fuel every year. And it is only going to get worse, a lot worse, as the water community struggles to find adequate supplies of water to satisfy a growing population, tries to find ways to treat water to remove ever increasingly miniscule amounts of known pollutants, and tries to cope with a bewildering array of newly identified contaminants.
Water utilities use energy to pump, treat, and deliver fresh water and collect the wastewater and treat it before disposal. While much of the agricultural water is untreated, municipal water treatment involves aeration (for taste and odor), sedimentation, filtration, and chlorination or other forms of disinfection. The primary use of electricity in the treatment process has been for pumping water during treatment and to storage before use by the customer. 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 U.S. Environmental Protection Agency is imposing new and more stringent regulatory standards 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. There are also contaminants, such as MTBE and Perchlorate, that require innovative and expensive new treatment facilities. These treatment technologies can increase energy consumption at a typical water treatment plant by 20 percent or more, and some plants may face even greater increases in energy use.
Water scarcity is a significant issue in much of the U.S. west of the Mississippi and becoming a more important issue throughout the U.S. as the population grows. The search for new water generally concentrates on two new sources: water reclamation and desalinization. Water reclamation is reusing treated municipal effluent. Reclaimed water use has been concentrated on purposes that do not involve human contact or consumption, such as landscape irrigation, golf course watering, and industrial cooling water. However, reclaimed water is now increasingly being considered for domestic water consumption. Even though water quality standards require complete retreatment of wastewater, there is a general public reluctance to directly use treated effluent (the "toilet to tap" controversy). A much more palatable approach, and one that uses even more electricity, is to treat the wastewater, and use the treated wastewater for recharging ground water aquifers. This water is now subject to yet another round of treatment and disinfection when it is withdrawn from the ground and before it is sent to the customers. This extra pumping and "double treatment" results in significantly higher energy requirements than for traditional water sources.
Desalinization is desalting brackish ground water, some surface water, or seawater. There are two primary desalination technologies in use today: reverse osmosis and distillation. In reverse osmosis pressure is applied to the salty water, forcing the water molecules through a semipermeable membrane. The salt molecules do not pass through the membrane, and the water that passes through becomes potable water. In distillation the salty water is heated to produce steam. The steam is then condensed to produce water with low salt concentration. Both are huge energy users. Energy constitutes about 50 percent of the cost of reverse osmosis desalination and is the majority of the cost in distillation.
The final uncertainty is what the impact of climate change will have on the water sector. One thing does seem apparent, that the timing and pattern of precipitation is becoming more erratic. Since traditional water development (i.e., dams) is both expensive and controversial, there is much interest in new storage sources for water. These generally take the form of ground water recharge or conjunctive use, in which water is stored underground during times of surplus, and used during times of need. This can require significant additional pumping use - to get the water to the storage field, and to pump it out of the ground during times of need.
If all potential solutions to our water problems require increased energy use, how can we manage the water industry's future energy needs? There are four areas of opportunity which, when used in conjunction with each other, can mitigate much of the future energy impacts: conservation, self-generation, demand reduction, and demand response.
Conservation is a mainstay of any coherent water policy. It is obvious that the less water existing customers use, the more water from established sources there is for new needs. There are significant improvements in customer water use efficiency that can yield spectacular results. For example, the population of California's cities grew by 3.5 million people in the last ten years, but overall water consumption has stayed the same. However, Pollyannas do exist who say we can save our way to the future and do not need anything other than conservation. There are limits to conservation. In areas that have been exposed to extensive conservation efforts we see a hardening of demand - there is some level of water consumption below which it is prohibitively expensive to conserve more. Conservation also does not adequately address the need for additional storage to save water during the wet periods for use during the dry periods. Finally, many conservation programs increase energy use. Agriculture, which is the largest end user of water in the U.S., is increasingly turning from traditional flood or furrow irrigation to sprinklers or drip irrigation, with significant water savings. These new water conserving pressurized pipe systems require pumps and extra energy to supply the pressure these systems require.
Self-generation is an increasingly viable option for water utilities, as the costs of the new generation technologies has dropped in recent years and the technology improved. Water utilities typically require large open spaces around their treatment facilities, particularly wastewater treatment facilities. These open spaces can be dedicated to electricity production in the form of solar installations. Wastewater facilities generate methane in the treatment process, which can now be used to produce electricity via fuel cells or micro turbines. Many water utilities site storage facilities at the higher elevations in their service area. With sufficient elevation small, in-conduit hydroelectric generators can replace pressure reduction valves. The economics of these generators depend upon their proximity to the water utility electric loads and, in some cases, the cooperation of the local electric utilities.
Demand reduction is the ability of water utilities to shift some of their electrical demand out of the on-peak period, usually via the use of storage or by installing extra treatment capacity at its facilities. Depending upon local electric utility rate design, such programs may result in bill savings for the water utilities.
Demand response is the ability of water utilities to reduce their electrical demand when called upon by the electric utility. This can be done via the judicious use of storage, depending upon current water demand conditions. In almost all areas of the country, the electric utilities will pay for the ability to call upon this demand drop when they need it, which may make such activity attractive to water utilities.
Water sector electricity use is poised to approximately double in the next decade or so if we do not implement some of these options to mitigate that increase. Many of these options require forward thinking on the part of the water utilities, and the realization of the electricity providers that they need to work and plan with the water community on their future electricity needs.
Lon W. House, PhD, CEM, CSDP, is a Water and Energy Consultant with over 25 years of experience. Dr. House has a Bachelors, two Masters, and a PhD in Engineering and Economics from UC Davis. He is a Certified Energy Manager (CEM) and a Certified Sustainable Development Professional (CSDP) with the Association of Energy Engineers. Dr. House taught engineering in Graduate School at UC Davis for a number of years and was the Founder and Co-Director for Hydropower at the UCD Energy Institute. He worked for the California Energy Commission as a utility planner, and was the chief utility planner for the California Public Utilities Commission.
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