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Study Suggests Planning for Grid-Based Light-Duty Vehicles (PHEVs or EVs) Should Factor in Impacts on Regional Water Resources

A study by researchers at the University of Texas at Austin has concluded that converting light-duty transportation from full gasoline power to electric power by using either plug-in hybrid electric vehicles (PHEVs) or battery electric vehicles (EVs) is likely to increase demand for water resources—primarily due to increased water cooling of thermoelectric power plants to accommodate increased electricity generation. The study assumes continuation of the current electricity generation mix, for methodological ease, even while recognizing that “changes will happen.”

The potential increase in usage, assuming wide-spread adoption of PHEVs and EVs, represents a significant potential impact on regional water resources and should be considered when planning for a plugged-in automotive economy, according to the study by Carey King and Michael Webber, published online in the journal Environmental Science and Technology.

The authors of the study, which has already been sensationalized with headlines such as “Plug-in Cars Could Drain US Water Supply”, are careful to point out that they are not saying that the negative impacts on water resources make the shift to grid-based transportation undesirable, but rather that such impacts should be quantified ahead of time to avoid unnecessary conflicts. The study concludes with the suggestion of several steps and policies that can be promoted to enable sufficient water access for enhancing PHEV market success.

King and Webber calculated that in displacing gasoline miles with electric miles, approximately 3 times more water is consumed (0.32 versus 0.07–0.14 gallons/mile) and more than 17 times more water is withdrawn (10.6 versus 0.6 gallons/mile) primarily due to the increased cooling needs.

Water consumption describes water that is taken from a concentrated source and not directly returned—e.g., a closed-loop cooling system for thermoelectric steam power generation where the withdrawn water is run through a cooling tower and evaporated instead of being returned to the source. Water withdrawal describes water that is taken from a concentrated source, used in a process, given back from whence it came, and available again for the same or other purposes—e.g., an open-loop cooling system for thermoelectric steam power generation that withdraws cool water from a reservoir into its condensing unit and discharges that heated water back into the reservoir.

The typical US driver would drive 4,500, 7,100, and 8,600 electric miles per year in a PHEV20, PHEV40, and PHEV60, respectively. For example, it takes 114, 72, and 59 million PHEV20, PHEV40, and PHEV60, respectively, to drive 500 billion electric miles annually. [Total miles driven in 2003=2.66 trillion] Since there are 234 million gasoline LDVs on the road today, displacing one-sixth to one-fifth of gasoline miles with 114 million PHEV20s, or 49% of the vehicle fleet, sounds feasible, but with annual sales rates of cars and light trucks/SUVs amounting to 17 million vehicles per year, it would take 7 years if every vehicle sold were a PHEV20. Comparing the displacing of the same 500 billion gasoline miles with electric miles of PHEV60s requires replacement of 25% of cars, light trucks, and SUVs, for which the tradeoff would be annual water consumption of 160 Bgal/yr compared to 35–70 Bgal/yr using gasoline. Also, 5,300 Bgal/yr would be withdrawn instead of 300 Bgal/yr. These increases in water usage represent approximately 0.2–0.3% and 3%, respectively, of overall US water consumption (100,000 Mgal/d freshwater in 1995) and withdrawal (408,000 Mgal/d in 2000).

...Water rights and access are also largely a regional issue due to varying laws, rain patterns, river paths, and groundwater supply. Thus, in order to implement the electron automotive economy where a substantial number of miles are driven electrically, the water demands need to be assessed on a regional basis. This means that some relatively wet regions of the United States may be able to support more PHEVs at lower cost than other relatively dry regions. Also, dry regions can focus on cooling techniques that require little water or electricity generation technologies, such as wind and photovoltaic solar that do not consume and withdraw water. Most importantly, public policy decisions that promote PHEVs or electric vehicles need to consider the impact on water resources beforehand because the increased demand for water withdrawals is potentially quite substantial and could impact water availability or rights for irrigation, municipal, and other competing purposes.

The authors suggest four initial steps and policies:

  • Promote research and development of distributed generation and renewable energy sources that use little to no water and can possibly be located onsite where PHEVs are charged.

  • Develop regional water plans that consider increased demands for electricity for PHEVs in order to ensure adequate water access in light of competing water demands for municipal and irrigation uses.

  • Move to generate more electricity by methods that do not withdraw such large amounts of water.

  • Use reclaimed, saline, or other water sources that are suitable for thermoelectric cooling, but unsuitable or unable to be treated economically for drinking.




Et tu, Brutus? This stupid headline is popping up everywhere. Waste of pixels.

Harvey D

Ridiculous and laughable.

How can a University fall so low. Must be from Texas?

Are these the same people who tried to convice the American drivers that a huge Hummer consumes less than a Prius.

Probably paid by the Oil Industries and ICE oversized gas guzzlers manufacturers?

Should not have been posted unless accompanied by a caveat.


the first tens of millions of cars will be charged with off-peak electricity, requiring no drop of extra water (and no CO2).
Anyway, it would be best not to waste hot water, because it is wasting energy.
Even if that is not a problem, I suppose the ocean has enough water to cool the powerplants. Since electricity can be transported very easily, they just need to build the powerplants at the right place. The amount of water needed to produce an equal amount of bio-energy is hundreds of times higher...
If I read correctly, a worst case scenario predicts a 3% increase in US water consumption for a 25% transformation of the vehicles. So 12% increase for 100% transformation. Small price to pay. (especially since the 12% could be seawater)

Rafael Seidl

Perhaps the first question should be what the primary energy sources for the additional electricity production will be. The implicit assumption here is that the mix will not change even if xEVs fleets become very large, i.e. they'd be driving on coal, gas and nuclear. This makes sense if xEVs are trickle-charged at night to take advantage of a lower rate, thereby improving capacity utilization of both plants and the grid.

Since most power plants get their cooling water from a river or large lake, increased load during the night simply means that water that would otherwise have passed a given plant by would now be used for cooling. In other words, no additional water would be needed. The only environmental impact on the river would be an increase in nighttime water temperatures, which could alter the ecosystem. While that is an issue, it must be balanced against the benefit of having large numbers of vehicles drive on something other than oil.

There would be some additional water consumption if the plant ran on coal or gas and, future emissions requirements prompted the operator to install algal bioreactors nearby. The CO2 produced during the night would need to be stored and added to the flue gases produced during the day. The algae would then use photosynthesis to split water and chemically reduce the CO2 to carbohydrates and/or oils.

GreenFuel is working on such systems today, if they can figure out how to scale up their technology it will be the most cost-effective way to implement carbon capture. After all, the alcohols or biodiesel produced from the algae can power ICEs so more oil can be left in the ground.

Another scenario in which cooling water could become a constraint in relatively arid regions is if large numbers of xEV drivers insist on rapid recharges during the day, as that would require the construction of expensive new power plants. E-REV hybrid concepts make this scenario unlikely.


Harvey this is not an attack on using PHEVs or EVs. It simply points out that the conversion from fossil to electric propulsion may create water resource problems if we choose old energy forms to generate this electricity such as coal, nuclear or natural gas. It is another good argument for using wind turbines that does not stress any natural resources in any important manner.

Pointing fingers of Texas is not fair by any means. Texas is already the state in the US that produces the largest quantum of renewable energy and they are speeding up installations of wind turbines like no other place on earth apart perhaps from China. The fact is that Texas has lately become a green energy leader and an example to follow.


I would rather have all relevant factors considered, whether it is cellulose biofules or PHEVs. It is the after the fact "gotchas" that really mess things up.


It is fair game, better to acknowledge it. Not that heavy oil or ethanol wouldn't use more. A major influx of EV/PHEVs could potentially send a water stressed area over the edge if local power generation is water-intensive. All the PHEV's effects are worth weighing if we plan on having a large number of them. As they become numerous they could help reduce water usage at times aiding with demand-side management using V2G, or acting as a battery for the growing number of solar projects to help meet peak demand.


Ethanol distillation takes 4 gallons of water per gallon of ethanol produced. Gasification might actually produce water from the dehydration of moist feedstock.


As an electric engineer, I have to say that I am dissapointed that this study is so skewed towards the worst case scenario. I say this because the whole point of going electric or plug in hybrid is to use renewable sources to power this vehicles. Let's use geothermal as an example. Geothermal energy is a fairly constant source of electricity and a geothermal plant produces electricity with negligeble down time (translation: electricity is produced for more than 97% of the time). So let's start with some assumptions: let's find out how many electric cars can be powered by a 100 MW geothermal plant if you can get 3 miles/ KW*hr and you drive the cars for 15,000 miles a year.

Miles/yr=100MW*24hr*365*(1000KW/MW)=876,000,000 miles/yr

Now let's see how many cars can be driven for 15,000 miles/yr:

# of cars = (876,000,000 miles/yr)/15,000 miles
# of cars = 58,400

So the next question is how many 100 MW geothermal plants have to be built in order to power the 16 million new cars that are sold in the US every year:

# of 100MW geothermal plants = 16,000,000/58,400
= 274 geothermal plants.
The beauty of geothermal plants is that both the hot water and the heat sink (cold water) are both under ground most of the times.

Notice that I purposely left out wind power (which does not need any water) and I also left out solar power.
In short, difficult: Yes, expensive: Absolutely, but if you look at the amount of money spent in Irak, is very doable.


On the face of it, the study totally neglects the vehicle to grid possibility - eg. with the vehicles charging at off peak tariffs and selling back to grid at peak rates: "You actually could SAVE copious amounts of water".

Justin VP

It is good to consider all the impacts, positive and negative, of a shift away from fossil fuels. Positive, long term change won't happen just by drinking the Kool-Aid. Potential nagatives must be identified so that they can be mitigated.

The availability of water is as big a long-term issue as is global warming. The two are directly linked, as GW may well have unknown and drastic impacts on distribution of world water supplies. If you don't have clean water to drink, not being able to drive your car suddenly doesn't seem like such a big issue.

I agree that there are many good strategies to avoid additional strains on our water resources as we move to decrease our output of CO2. Identifying the issue is the first step towards solutions.


"A major influx of EV/PHEVs could potentially send a water stressed area over the edge if local power generation is water-intensive. "

most water-stressed areas tend to receive a lot of sunshine. all the more reason to accelerate the expansion of concentrated solar power plants. when life gives you lemons, make lemonade?

Adam B.

Some of these reactions are a little bit over the top (knee-jerk even).

If you move the point of conversion from chemical energy to work from the IC engine to a centralized generation facility, there are of course going to be water impacts.

The use of renewables will help to mitigate this trend, but we are not to the point yet where plug-ins will be generally powered by renewables.


Effing lame! Can't even get it's terminology straight. In a closed-loop system the water doesn't escape, it just keeps going around because the system is closed.

Stan Wellaway

We do seem to be experiencing quite a few sensationalist headlines this past few weeks, aimed at scaring folk away from developing electric vehicles. Usually channeled via some university or other to make it sound impressive - when much of the supposed science is distinctly amateurish and incomplete.

I'm not given to conspiracy theories, but if it is all part of some campaign, they've left it too late. There are now far too many players actively involved in developing EVs, in too many countries.

In transport, the future is electric. And those who see problems in that would probably be better employed in helping overcome the hurdles rather than trying to stop the race.


Adam. Nor are we at the point where we are actually using any EVs or PHEVs. They will come in some larger numbers starting from 2011 and at that time new installations of renewable energy will make up the majority of new capacity added to the grid in Europe and the USA. Things are changing much faster at the moment for renewable energy than any prognosis had predicted. For instance, the US added 5000 MW of wind power to the grind in 2007 up 50% from 2006. This is more than enough to power all new EVs and PHEVs at any likely scenario. It is therefore very reasonable to assume that all EVs and PHEVs will be powered by renewable energy even in the US.

Furthermore, conservation is a colossal untapped resource for the US grid. California is one of the most affluent parts of the US and yet they manage to spend only roughly 60% of the average US electricity per capita. If average electricity consumption in the US could come down to the California average the saved electricity would be able to power most of the conversion from fossil fuel to EVs and PHEVs in all of USA. In any case the fact is that there are huge environmental net benefits from EVs and PHEVs no matter how we look at it.

"Effing lame! Can't even get it's terminology straight. In a closed-loop system the water doesn't escape, it just keeps going around because the system is closed."

DS: What you say makes sense.

I wondered about the cloaed and open loop. It seemed an odd use fo 'closed' and 'open', But I don't know much about generation matters so I kept quiet.


I find it hard to believe there is anything to the water concerns. Plug-in sales will be widely distributed across the country so the load will ramp up slowly.

The utilities can handle their part provided they are actually allowed to build. The bigger problems are fuel and emissions.


The study does not take into effect of water conservation. I see actions on energy conservation, and water conservation as necessary going forward. Assuming lots of energy conservation (PHEV, BEV), but at the same time no water conservation is quite flawed.

Felix Kramer

We posted the author's response to the sensationalist headlines and misinterpretation of the study at

And this afternoon, a somewhat more balanced report appeared at ScienceNOW

-- Felix Kramer, Founder,


Lets see...
First you change out a couple light bulbs with CFLs, maybe even a put in a programmable thremostate, some good insulation, energy star appliances, and then throw some solar panels on your roof... and were good.
No worries.


By the time PHEVs and EVs begin to be sold in meaningful numbers, renewables (solar, wind et al.) and conservation, e.g., LED lighting, will begin to displace these water guzzling thermoelectric power plants. The deployment of PHEVs and EVs will coincide with the resultant decrease in water demand from thermo plants.


Cooling doesn't necessary means evaporation, I found hard to believe that so much water is evaporated in the process of cooling power plant, but I contend that I never checked that. The solution is to locate the power plant near the seashore and use these wasted heat desalination of sea water, then the balance would be positive and not negative.


Globe average water vapor residence time in atmosphere is less than 9 days. After that water vapor comes down as rain or snow. Most of the evaporated in cooling towers water will return (except in locations downwind to ocean) to the ground, and will be used more and more times. This effect is well known in irrigation: massive irrigated agricultural areas increase rainfall downwind. And compared to agriculture, water evaporation (not usage as defined in water permits) is laughably small. One glass of orange juice, for example, requires 1000 glasses of water for irrigation (and most of it is returned back to ground to be used once again).

joe padula

Thank God oil refineries do not use any water!

Or the many liters of water they use per liter of fuel processed would save water as gas consumption went down.


I'd just like to put this out there:
(In this context, "consumes" means evaporates)

Oh yeah, and as for oil refining water use.

Not only is it extremely water intensive, but it also creates a toxic sludge out of it, rather than freeing it up later.

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