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Water Offsets for Green Buildings
Jeremy Faludi, 9 May 07
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Green buildings do many things to save water, sometimes spending thousands of dollars to do so. But what if they could save double, or 10 times as much water for the same cost? And what if they could help bridge the rural-urban divide while they were at it? This could all happen with irrigation offsets.

As we've written before, cropland irrigation uses vastly more water than cities do. The amount of water wasted by inefficient irrigation is around four times the total amount of water used by commercial and residential buildings. So why spend thousands of dollars on greywater capture systems, low-flow toilets and showers, and other building improvements, to make an already tiny slice of the pie a few percent smaller?

Builders might have a bigger impact by financing water offsets--buying an efficient irrigation system for a farm or orchard somewhere. I was curious whether this would really make sense financially, so I ran the numbers on it, in a back-of-the-envelope way. It doesn't save as much as I'd initially thought [thanks for the correction, Nic], but the numbers are still impressive, especially for buildings in the dry southwestern US.

The cost to outfit a small office building with entirely low-flow fixtures (toilets, sinks, showers, etc.) is hard to calculate, because the prices not only vary a great deal, but are unavailable to the public. (Multiple places I called would not give price information to anyone but contractors, and the two architects I talked to had no idea of the numbers either.) So I took something easier to compare: the cost and water-saving of waterless urinals vs. normal ones. Waterless urinals cost about $500 - $600 apiece, while comparable status-quo urinals are $150 - $300. Let's say there's a $300 additional cost for being waterless. A small office building might have 20 urinals--this would be an added cost of $6000 for saving water in the building. The Presidio of Monterey did a study of their water savings after installing low-flow systems, and found that their 173 waterless urinals saved 0.755 acre-feet per month. That's just over 17,000 gallons per year per urinal. (An acre-foot is the amount of water required to fill an acre of land one foot deep. It's the standard unit of measure in large-scale water use in the US.) Your $6000 for 20 urinals will thus save you 340,000 gallons per year total. Sounds like a lot, right? Just wait.

The cost of a drip irrigation system for a small farm varies a great deal, and there are many sites that give estimates, but for good average numbers the Western Area Power Administration (getting data from Washington State University and the Idaho Department of Water Resources) says "Center pivot [sprinkler irrigation] systems have a total 'in-field' cost of $600 to $1,000 per acre... Drip or trickle systems cost $800 to $1,600 per acre". So let's conservatively say that it costs $600 more per acre to install drip irrigation. That means that when designing your small office building, instead of putting in 20 waterless urinals, you can take the same money and replace ten acres of sprinkler irrigation with drip irrigation.

How much water does ten acres of drip irrigation save? EnergyIdeas (a project of Washington State University) says "The 'water application' efficiency of a center pivot system ranges between 60% to 85% with an average of about 75%... The drip or trickle system has an efficiency of 80% to 95%, with an average of 90% assuming good water management practices are used." Those percentages must, of course, be applied to the total amount of water used. The USGS says that in the year 2000, "The average application rate [of irrigation water] was 2.48 acre-feet per acre for the United States". In many regions it is higher (California uses 3.37 and Arizona 6.21, for instance). That means that on average, a sprinkler system wastes .62 acre-feet per acre per year, and a drip irrigation system wastes .248 acre-feet per acre per year. So switching from sprinkler to drip irrigation saves .372 acre-feet per year per acre.

For our ten-acre farm, that saves over 1.2 million gallons per year--three and a half times the amount of water saved by spending the same money on waterless urinals in the building. And remember, this is a conservative estimate. If you were converting an Arizona farm, you might save 8.8 times as much water per dollar. The only way a building's plumbing even comes close is if it is a super-high-traffic building like an airport, where people are coming through and using the bathrooms constantly--in cases like this, one manufacturer claimed in Grist that a waterless urinal may save up to 40,000 gallons per year; even there, though, you would still save half-again the amount of water per dollar by having a farm irrigation offset.

Other Benefits

Drip irrigation also saves energy by requiring less water pumping. The EnergyIdeas article above estimates that "A 15% improvement in water application efficiency is thus expected to provide a 16.6% reduction in pumping system electrical energy use." Or, for absolute numbers, a study by the University of Florida said "Electric power units were estimated to consume 347 kw-hours per acre per year for crop maintenance drip irrigation and 432 kw-h/A for sprinkler irrigation." So our ten-acre farm would save 850 kilowatt-hours per year as well as saving water. This isn't a big amount of energy--roughly what you'd get by replacing nine incandescent lights with compact fluorescents--but it's a nice bonus. However, if you were building a single-family home instead of an office building and spent the same $6000 on water offsets, this bonus energy offset could be up to a quarter of the home's energy use.

A water offset like this might also help bridge the cultural and political divides between wealthy urbanites (who tend to create most environmental legislation) and rural farmers (who are often impacted by environmental legislation). Partnerships between buildings and farmers could be the perfect introduction to community-supported agriculture (the farmer could grow some produce used in an office cafeteria, or which employees sign up to buy), and perhaps other connections could bloom as well (using the farm for occasional retreats).


The hard part about setting up water offsets for buildings is the time spent finding good candidates to switch their irrigation systems. It might only work for very large buildings who can afford to hire a person to make the connections. Or it might require an intermediary firm to find the farmers and connect them to the architects, just like carbon offset firms act as intermediaries between consumers and the wind farms or forests being used as offsets. Problems like this have been solved before, however. William McDonough once told a building developer to plant ten square miles of forest to offset greenhouse emissions for the building being built, and there are half a dozen different carbon offset firms in North America alone. It may just be a matter of time before water offset companies exist alongside (or as part of) carbon offset companies.

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Cool idea, Jeremy. It's all too seductive to get caught up in greening what's right in front of us, when it's usually the unglamorous industrial backstage that's responsible for the bulk of the devastation.
I wonder, though, if it's even appropriate to label the concept as an "offset". Whereas carbon offsets are supposed to cancel out the climate impacts of an action, what you're suggesting would likely far surpass the water usage of the building that pays for it. Rather than an offset, then, it's more of an investment: a small contribution that gets a lot of bang for the buck.

Posted by: Adam Brock on 9 May 07

It sounds good but will the price of waterless urinals come down as they become the norm rather than the exception? Like compact fluorescent bulbs which used to cost $10 but now cost $3.

Posted by: thatphil on 10 May 07

It sounds like a great idea, but to me it seems like your telling building owners and developers to go a head waste the water, they shouldn't care about the water they personally use because some one else is using a lot more. And anything they do will not have an impact.
Industrial processes use way more electricity than commercial buildings it doesn't mean you shouldn't put efficient lighting in and use the T12's and incandescent, then buy an offset from an industrial company.
The farmers can be shown the cost and environmental benefits of drip irrigation to make the change on there own as good business sense. Why not have government mandates to eliminate irrigation systems that waste extreme amounts of water and give incentives for installing drip irrigation systems. That way buildings and agriculture will use less water, conserving our most precious resource.

Posted by: Dave Palibroda on 10 May 07

Something about this just doesn't sit right. If the benefit was to go to a non-profit farming operation, say...producing drought resistant native seedlings to replace water hungry introduced species then fine. But for a commercial farmer to just be handed something like this seems a little...unfair? Why one farmer and not the other?

Would it not be better to make the cost of water higher, thereby making such measures more cost effective for the farmer to introduce himself? Or perhaps you could market your crop as being more water-wise giving you a point of difference?

How about this though. What if you were to subsidise the introduction of such efficiency measures across a region and in return get the rights to the water saved? Given the current cost of water rights here in Australia, and the long term trends as far as population growth and climate conditions go I think it might have some commercial merit.

And why stop at water? I've been playing with the idea recently of Carbon T-Raiding (ended up on a Gordon Ecco, Carbon T-raider Green is Good tangent which was kinda fun) based on commercial property portfolios. Renovate existing buildings to a high Green Star rating but retain the rights to the Carbon you've saved through your improvements to the buildings' performance. Tenants benefit from improved running costs and working environment, developer gets something out of it too.

While I'm here I should plug the building I'm currently working in. Council House Two here in Melbourne. Well worth checking out.

Posted by: Matthew on 10 May 07

A great idea in many cases, but let's remember that water can be limited at the source or at the sink. That is, irrigation offsets, if they encourage larger flow of water in the built environment, don't reduce burdens of sewerage-treatment systems, combined sewer and storm water overflows during heavy precipitation, etc. One important reason to save water in buildings has more to do with what goes down than drain than what comes out the faucet.

Posted by: David Foley on 11 May 07

David, good point about water use at the sink end (stormwater & sewage runoff). That's a good argument for keeping the low-flow fixtures in buildings themselves.

Also, everyone, if you read the article before, please re-read it now--someone pointed out a mistake in the calculations, which I've fixed. The gains are no longer so astronomical. However, they're still dramatic: from 3.5x to nearly 9x water savings per dollar.

Posted by: Jeremy Faludi on 12 May 07

In addition to what David said, it's also important to consider that water being made available to city users must (in most cases) be treated before use. When a city grows in population, water usage increases, often requires new pre-use treatment plants to be built. Increasing water efficiency in urban areas allows for popluation growth wile decreasing the need for new treatment plants, which has obvious benefits.
Working to decrease both water waste in both areas is the ideal.

Posted by: Michelle on 17 May 07

Jeremy. Great to see this concept bandied about. I have been turning this "water offset" over in my head for over a year now as a concept to be discussed in parallel to the carbon offset. As some readers point out, it is not a perfect analogy. In fact, in the specific way I have been designing it for my NGO, as a simple tool for individuals/families to calculate their water footprint, reduce the size of it, and then offset the remaining footprint in the form of donations to imy international partners doing water projects in the developing world, it gets even more complicated. Call it an "onset" instead; whereby carbon emissions offset by investing in ways to reduce/remove them from the atmosphere, water offsets should intend to reduce inefficiencies, increase conservation but also increase available water supplies in areas of water stress. I call it redistributing the water wealth of the world. I'll elt you know if I ever get it perfected!

Posted by: Rob Steiner on 18 May 07

Did you ever check out The best website for the environmental movement...

Posted by: on 21 May 07

Subsidizing efficient irrigation in lieu of builing water efficiency is an interesting idea, and seems akin to purchasing green power credits in lieu of, or in addition to, being energy efficient or generating your own power. An often used rule of thumb in green building is to first reduce your consumption needs, then meet them sustainably. I'd have to recommend owner responsibility, to use water efficiently in the building they can control first. If additionally, water offsets could be purchased to subsidize efficient irrigation that'd be the icing on the big-picture cake. A water offset program could be a great NGO or utility program - both commercial and residential consumers could purchase offsets. Water is one of the top global sustainability issues, along with carbon, species diversity, & human health - and of course they're all linked. We need water for drinking and food production first, so let's reduce it's use as much as possible for flushing our waste and washing our hands at the office.

Posted by: Teresa Burrelsman on 22 May 07



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