We’ve all learned that turning off the light when we leave the room, switching off computer monitors when not in use, or using energy efficient appliances results in a corresponding reduction in energy consumption. Similarly, turning off the tap while brushing your teeth or harvesting the rain water that falls on your roof will reduce your dependence on the municipal water supply system. What isn’t so apparent is the cascading effect that the aforementioned actions have. One effect is the reduction in water consumption for producing that energy in the first case. Another effect is a reduced power requirement to extract, treat, and distribute water to your home, since less water needs to be sent there.
Relationship status: it’s complicated… or is it?
Though not evident on the surface, energy and water share a significant mutually dependent relationship. Due to the increasing strain on both resources, it is imperative that long-term sustainability (in both intent and action) is driven by understanding this relationship.
Let’s look at this nexus from a more granular level. Producing energy in conventional power plants requires a significant amount of water (in relation to the power produced) – to spin the turbines in a hydroelectric plant, to produce steam for thermal power, and to cool the plant equipment. Much of the water is lost to evaporation as well. In general, between 25 and 60 gallons of water is extracted/ withdrawn to produce one kilowatt hour of electricity.
Though some renewable energy sources (like solar and wind power) do not require much water for actual energy production, water is required to produce their raw materials.
In a reversal of roles, energy is consumed at almost every stage of the water cycle:
- extraction
- treatment
- distribution
- end user consumption
- waste water treatment
The numbers game
The California State Water Project and Central Valley Project together are the largest consumers of electricity in California. They consume a whopping 10 terawatt hours of power every year. These energy guzzlers aren’t alone, though. There is smaller, fragmented consumption in the form of private ground water pumps and energy used for residential water heating. They contribute equally or even more so (during the summer months) to the water-related energy consumption pie.
An often forgotten variable in this equation is the energy spent transporting the water from its source to the end user. We return to California as an example. In 2005, the energy required to ship water from the rural and wetter north to the more populated south was 12.7 million watt hour per million gallons. This reality applies not only to California, but to most of the grid dependent cities throughout the world. If rainwater harvesting was to become the norm rather than the exception, we could see a drastic reduction in energy production and its associated ill effects.
Going forward, energy and water should not be looked at in silos when formulating action plans for their conservation. What appears to be an attractive plan to conserve energy may result in a severe strain on water resources. Instead, the key is to achieve an optimal balance between energy and water use.
References:
https://en.wikipedia.org/wiki/Water-energy_nexus
http://www.ucsusa.org/clean-energy/energy-water-use/energy-and-water#.WHDtzVOGNdg
https://www3.epa.gov/region9/waterinfrastructure/waterenergy.html
http://www.ucsusa.org/clean-energy/energy-water-use/water-energy-electricity-overview#.WHEBdVN95dg
https://water.usgs.gov/edu/wupt.html