The carbon footprint of the water we drink
Recently I did a presentation for the Eco Green Group of Silicon Valley on the Water-Energy Nexus. Typically, the group advertises its meetings on Meetup.com. After my talk one of the organizers of the group informed me there we a question asked by someone on meetup.com who was not able to attend my presentation. Most non-profit encourage their members to participate so I thought I should take the time to answer the question.
Carbon footprint of the water we drink
The question was, “what was the carbon footprint of the water we drink?” I thought about the question then recalled I reported a statistic that the carbon emissions related to water in 2005 were approximately 290 million metric tons, or 5% of all carbon emissions in the United States. I thought would be interesting to dig into the question a little further. I came up with the following a day later.
Energy use in water results in carbon emissions
Clearly, a significant quantity of energy enables our daily use of water. Whenever water is moved uphill, treated, heated, cooled, or pressurized, energy is needed. Most energy production emits carbon dioxide (CO2), which contributes to global warming. Therefore, water use is another, often overlooked, contributor to our individual and collective carbon footprint. Better decisions related to water treatment and use can help reduce the extent of energy consumed throughout the water use cycle which can minimize energy use, reduce the associated carbon footprint, and protect our freshwater resources.
Breakdown of the amount of energy required for domestic water
Upon further investigation of your question the energy required for domestic water use varies widely from place to place. For water estimates for energy use and carbon emissions are broken down into three components: 1) water production, 2) residential use, and 3) water waste treatment.
Calculation of Carbon footprint
The energy requirement for each of the component is calculated from which the equivalent amount of CO2 is determined. The energy requirement would be the energy to pump the water from its source to your house, heat the water in your house, and pump it back to the Waste Water Treatment Plant (WWTP) for treatment.
The sum of these three footprints gives you the overall CO2 equivalent. With the total footprint in hand and total number of gallons used allows determination of the footprint per gallon of water.
The Energy Intensity, in Kilowatts hours per millions of gallons of water, is used instead of the overall energy as well which would eliminate the step of needing to know the overall gallons of water under consideration.
Thanks for asking
I wish the person who posed the question had attended my presentation so we would have had the opportunity to meet face-to-face. But I was glad he asked the question because I was able to learn something I previously had not thought of. So thank you for asking and hopefully we have both learned something.