How big is this connection? What percent of our nation's energy goes to water in some fashion? If the connection is large, what can we do about it?
In 2005, with the release of the California Energy Commission Integrated Energy Policy Report, the State of California began to address these questions by bringing together policymakers from its energy and water agencies, along with a variety of stakeholders. What these different groups discovered was that, although the connection between water and energy is large, addressing the synergies between the two provides opportunities to address several of pressing issues, including greenhouse gas emissions and climate change.
For those compiling the California Energy Commission, 2005 Integrated Energy Policy Report, the first step involved the creation of a common language, so that the water and energy folks could communicate with one another. Defining the water-use cycle, via the Water Use Cycle Energy Intensities chart, provided that common language (See Figure 1).
The water-use cycle illustrates how water is taken from the environment, treated, and delivered to a customer. After the customer is done using this water, some of it is directly discharged, while the rest is first collected and treated before being returned to the environment. An additional community recycling level is also shown within the water use cycle boundary.
In order to get a better picture of the information contained in the Water Use Cycle Energy Intensities chart, it is important to note the extremes in terms of energy demand: zero for gravity-fed supply and conveyance is water, (such as from Hetch-Hetchy dam) versus 14,000 kWh per million gallons to lift water over the Tehachapi Mountains. This wide range of energy consumption covers most of the country. The additional 16,000 kWh per million gallons noted for water treatment includes the energy needed for the currently available ocean desalination plants.
It is also important to note that the energy consumption for water treatment and wastewater treatment is largely driven by health requirements; once the level of treatment is determined, then the choice of treatment type drives the energy consumption per unit of water. The range for the entire water use cycle is 2,000 to 20,000 kWh per million gallons.
So, how much energy goes to the water use cycle? It depends on where you live. For example, the biggest variable in California is the energy needed for supply and conveyance. Gravity-fed water serves approximately one quarter of the state’s population, and roughly half of the agriculture. This brings the average for northern California down.
On the other hand, most of southern California is served by imported water, either from the Colorado River or from the State Water Project, which brings the average way up.
The point here is that you need to determine the amount of energy needed to deliver water where you live, remembering to count all parts of the water supply and wastewater treatment cycle; including water supply, treatment delivery, and wastewater collection, treatment, and discharge.
In aggregate, somewhere around 5% of California’s electricity consumption use goes to the water use cycle. Most of this is central station-generated electricity, with some of the energy coming from natural gas and diesel. An additional percentage comes from on-site distributed generation, usually in the form of biogas-generated electricity.
Most surprising, is that, ultimately, the water use cycle does not represent the majority of the energy use that is attached to water: most energy usage is added by consumer demands. Have you ever been to the top of a tall building? Was cold water up there? How did it get there? Was there hot water too? How was it heated? Do you know anyone who has a clothes dryer? Isn’t its purpose to take the water out of the clothes? Have you ever seen a building with a chiller for air conditioning? In the summer, it evaporates water to create “coolth,” so every unit of heat you don’t have to take out of the building is a unit of water that you don’t need at the chiller.
When all of these factors are accounted for, an additional 14% (pumping, drying, air conditioning, water heating) of California’s electricity (for a total of 19%), 33% of the natural gas (water heating in residential, commercial, and industrial applications), and a significant amount of diesel (on-farm pumping) go to water in some form. By adjusting California’s percentages for United States, the results indicate that roughly 20% of the nation’s stationary energy use, and the proportionally associated greenhouse gas emissions, go to water use in some way.
Several synergies where joint efforts would seem to be most effective include:
1. Saving water saves energy:
The water we don’t use saves the energy for the water use cycle. In addition, it saves pumping, treating, drying, or heating in our buildings. Saving hot water at the top of tall buildings, in the portion of your community with the greatest energy intensity of the water use cycle, is the place to start.
2. Saving energy saves water.
The discussion above only looked at the water saved if you had a chiller for your building. However, most of the nation’s electric power plants use water for cooling at roughly 0.5 gallons per kilowatt-hour generated. Wherever this water is potentially potable, we should also count the water that could be saved from generating electricity; so all customer efforts to increase the efficiency of electricity use become part of the solution too.
3. Improving the efficiency of water distribution and wastewater treatment facilities is another synergy.
This includes the selecting of the most energy-efficient treatment process to meet the required health code. It also includes choosing the right diameter pipe to deliver the water or collect the wastewater, thereby reducing the power requirements of the energy
efficient pumps.
4. Generating energy from renewable sources is still another aspect of the solution.
Water delivery and wastewater systems are generally located near energy load centers. Using the biomass in the wastewater treatment plant is already being done, but, in some cases, the electricity generated in limited by what can be used at the treatment plant, not by what could be produced by the available supply of fuel. Many facilities have land that could be used to generate electricity from solar, wind, or in-conduit hydro. And, what about using the available biomass to make fuel for the vehicle fleet?
So, where do we go from here? Bring together the water, wastewater, and energy suppliers in your community. Count the energy needed for the water use cycle. Focus on the synergies. I think you will find that water use efficiency is the next “gold mine” for increases in energy efficiency, and renewable energy production and greenhouse gas reductions.