Rainwater Harvesting for Drylands and Beyond by Brad Lancaster

May 10, 2010


By Brad Lancaster

© 2010 www.HarvestingRainwater.com

Watergy is a term coined to describe the interconnection of water and energy. Every time we consume power we consume water. This is because water is used in the generation of our power – in Arizona this figure ranges from 0.001 to 56 gallons of water per kWh of power consumed.1 Therefore, anything we can do to reduce our power consumption also reduces our water consumption.

Typically the amount of water consumed during power generation is much greater when the power is generated at centralized power plants, as opposed to on-site with renewable power production such as rooftop solar, whose water consumption is negligible.

Introducing a Watergy Cost Calculator for You and Your Community

How much water is expended in the generation of electricity from different sources?

How much energy, and subsequently embedded water, do average U.S. and Arizona households use per month, depending on where their energy comes from?

How about you and your community?

Use our interactive online Community Watergy Calculator to find out.

The Watergy Cost Calculator. Notice how a Tucson, Arizona, household consumes 558 gallons of water per month via its electricity consumption if it gets its power from coal (the primary source of electricity in Tucson), but consumes only 1 gallon of water per month via its electricity consumption if it gets its power from rooftop solar. Now let’s go up in scale. Notice how all Tucson households combined consume 112,161,890 gallons of water per month via their combined electrical consumption if they get their power from coal, but they would consume only 219,925 gallons of water per month via their combined electrical consumption if they were to get their power from rooftop solar. Click the image above to visit our interactive online Watergy Calculator, where you can enter the number of households in your community to generate ballpark numbers for how much water your community consumes through its power generation.

The Community Watergy Calculator was conceived of by me, and created by Megan Hartman, based mainly on watergy data for Arizona from this wonderful and succinct resource “The Water Costs of Electricity in Arizona.”

Still more watergy information can be found at www.harvestingrainwater.com/water-energy-carbon-nexus.

Before I speak or teach in various communities, Megan generates one-page Water Conservation and Climate Data sheets (newer versions contain additional information for site analysis and are called Patterns of Climate, Water Per Capita, Watergy, and Sun) for those communities. Many of these are available here, with more being added on a regular basis. These spreadsheets also list:

• What percentage of the community’s energy consumption is used to move (or move and treat water), or the number of average energy-consuming homes that could be powered with the energy used to pump/treat water, depending on the data we are able to obtain.

• How much rain per person per day falls on the community in a typical year (rainfall GPCD) compared to how many gallons of municipal water per person per day are consumed in a typical year (municipal GPCD). In most cases, per year, a greater volume of rain falls on the community than is provided by the municipality. This helps make the case that if the community were to harvest and utilize more of that free, high-quality rainwater, it could reduce or eliminate its depletion of local water sources, and reduce or eliminate the “need” for the high cost/high energy importation of water from elsewhere.

Patterns of Climate, Water Per Capita, Watergy and Sun for Tucson, AZ. Notice how the average Tucsonan uses 112 gallons of municipal water per day. And notice how during an average year there are 198 gallons of rain available per person per day – if only we were to harvest that rain and make it available throughout the year. To arrive at this rainfall GPCD figure, the spreadsheet calculates how much rain falls on the surface area of Tucson in a year of average rainfall, then divides that figure by 365 (days per year), and then divides the result by the population of Tucson. Also notice that 44% of the City of Tucson’s annual municipal energy consumption is used to move and treat water.

For updated Patterns of Climate, Water per Capita, Watergy, and Sun for many locations around the world see here

For simple and effective tips on how you can greatly reduce your energy consumption at home; increase your on-site passive heating, cooling, and solar power production; and enhance comfort and productivity, see Chapter 4 of Rainwater Harvesting for Drylands and Beyond, Volume 1. The whole book is packed with great info on how you can make progress on goals like these, while greatly enhancing the potential and use of your local rainfall, stormwater, greywater, and more.

For updated water-energy-carbon nexus tables see here

1. Extrapolated from Water Costs of Electricity in Arizona, a Project Fact Sheet of the Arizona Water Institute (Tucson, Arizona) from a 2007 investigation by Pasqualetti & Kelley. Fact Sheet ID: AWI-07-102 Pasqualetti.

2 Responses to “Watergy”

  1. Josh Landess Says:


    It’s well-done to publish this, especially the link to the spreadsheet and to the other related links on the site, …. and we can see by the dates on the links and the files that you’ve been publishing on this topic for some time.

    It’s well-done by Megan Hartman for putting together the sheet and the calculations, and it’s an interesting part of your presentation that you are able to present to a small place some of their own data when you speak.

    I saw your presentation in Patagonia and now see this further followup on this watergy topic, which of course is only one of several topics that you covered very well.

    As soon as you taught me the word “watergy”, a light went on with me, and to some extent with my colleagues.

    I thought of it and think of it going in at least two directions:

    1. water used in generating energy.
    2. energy used in preparing water for use.

    For the most part, your calculations above and on the other watergy [I note that the spell-check on this browser field does not process the word watergy….:-)] links on your site seem to bear on #1, and for a little while I thought #2 was absent. However, if we look for it, we can see that you cite Bruce Plenk’s extremely helpful numbers:


    [Bruce Plenk, City of Tucson Solar Energy Coordinator]

    % of City’s annual electricity consumption used to move water: 50% 2007-8
    % of City’s natural gas consumption used to move/treat water: 88% 2007-8
    % of City’s total energy consumption used to move/treat water: 44% 2007-8

    The 44% total energy number is also here on this May 10, 2010 blog, above.

    Even though it’s not highlighted, I’m glad to see this second part of the watergy issue brought out. It really set me to thinking when you provided this estimate.

    On the first point, which is more the focus here, I have a comment and a question. My comment is that, amongst other things, this research helps bring out the strong need that we have to identify and use alternatives to solar thermal high-water-use. Perhaps there are lower-water-use methods. One person in California told me that generally when they propose projects there (or was it here?) that they don’t at this point propose solar thermal unless there is some alternative (even if less efficient) used to conventional water.

    My question is to define “use”. In other words, if water is “used up” in the process of generating electricity at a coal plant, then how far away is that particular water from being rehabilitated to the point where it can be re-used. Does it necessarily have to be vented and found again “some day” or can it be processed efficiently and used to water plants or re-used directly over and over again in the coal plant?

    Likewise for the other uses… would they each not have some level of nuance of how much they are used up and how much energy and other resources it would take to rehabilitate that water… and to what level of usefulness?

    Going back to point #2, I think it will be good if you can fill in that data with even more data points from other cities and utilities and others…. I wouldn’t go looking for data that is the same… perhaps it will be dramatically lower or higher in other areas, as to how much energy is needed to move and process water.

    Lastly, a math comment to Megan, I’m not sure but I’d be curious to tie the two sides together. That is:

    – you use x number of gallons to generate useable energy.
    – you then use y number of megajoules (or BTU or KWH or whatever… megajoules are the SI Unit I think) of energy to move/treat water.

    – you then go back and use x number of gallons to generate use-able energy, but in so doing, you can see how many Megajoules are already a component of that x number of gallons. So, it’s as though you’ve used energy even before you’ve generated.

    I don’t think this calculation can be done in a meaningful way at present, or maybe ever. At present, I think there needs to be a bit better perspective on point #2 (how much energy goes into preparing water for different types of uses and at what point in the value chain). For example, in his presentation, Brad said that the Tucson numbers should be understood as being after the water hits Tucson…. that is, it’s not even counting what it takes to get some of it to Tucson. So, that’s just one thing that makes me think it would be hard to do any meaningful math here…. and I don’t know ultimately if you can. We can be aware though that each gallon of water has in it an “energy expended component” to prepare it, just as we can be more aware that each Megajoule of Energy has a “gallons of water used to generate it” component.

    I like this page,


  2. Sun- & Shade-Trap Videos - Planet Experts Says:

    […] not only saves water associated with power generation, but also significantly reduces the water needs of the garden, since the shaded and cooled plants […]

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