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Exploring the home energy angle in a water crisis

Faced with a "boil water" order in Massachusetts, CNET's Martin LaMonica dives into the complex and fascinating question of the most efficient way to boil water.

Moments before heading out for dinner this past Saturday night, I learned I was living in what you could call a dry town. Along with 2 million other people in the Boston area, water service to my town was disrupted because of a "catastrophic" break in the distribution system.

Early Saturday morning, a collar attached to a giant water pipe in Weston, Mass., broke off, which cut off the source of clean water to 30 cities and towns. Two days into the crisis, people in the area are now being supplied by a backup reservoir system that requires people to boil any water they consume.

Face off in an energy-efficiency duel! Martin LaMonica/CNET

Obviously, this is a serious situation, which officials hope will be resolved within days. But in my household, the "boil water" order raises a practical question: what is the most energy-efficient way to boil water?

This seemingly simple question, posed by my wife Sunday morning, launched hours of Internet searching and a mini science experiment at home. After vacillating between the electric kettle and gas stove to boil water all day Sunday, I feel like I've now unraveled a great mystery and can, for the moment at least, proceed with more confidence.

Apart from this curiosity-piqued sideshow, the entire episode is a sharp reminder of how important access to fresh water is to our daily lives. Yet, as a resource, people don't expect to pay much for it and it's an area that sees relatively little technology innovation or investment.

Where's my beaker?
Nailing down the answer of energy efficiency and water boiling is more complicated than it seems. If you poke around the Internet, you can conclude fairly quickly that electric kettles are far superior to microwaves and electric stove tops. It gets trickier when you bring gas into the equation, with both gas stoves and electric kettles being good options on the efficiency front.

I found a number of analyses heaping kudos on the lowly electric tea kettle, including this one from Treehugger last fall. In short, kettles blow the other electric options away because they are designed for efficiency. They are the best at transferring the energy from the heating element to the water, compared to other methods, which lose more heat to the air.

In my home, though, it came down to gas or the electric kettle. As an added wrinkle, I get almost all my electricity from solar panels, particularly during the long days of spring and summer.

Setting the solar bit aside, I focused on how much energy is required to bring water to a boil. Depending on how long this goes, it may actually be noticeable on our bills.

Using a Kill A Watt power meter, I measured how many kilowatt-hours were required to boil a liter of water. Then, I measured how long it took to heat a liter on the gas stove. I got an estimate for how many BTUs an hour my stove's burners are good for and then converted the total BTUs needed to kilowatt-hours.

At first blush, the kettle uses less energy than the gas stove. However, the two sources are awfully close in total energy consumption when you consider the amount of fuel that is required to generate electricity and deliver it to your home.

The best recommendation I could find is that going with a gas kettle is a good way to go in winter when you can benefit from the heat it gives off.

The data
In the U.K., where people boil water to make tea many times a day, this issue has been studied intensively. For the actual analysis, I defer to David MacKay, a professor of natural philosophy at the department of physics at the University of Cambridge. He is the author of Sustainable Energy Without the Hot Air, a book that takes a look at big picture energy needs through the lens of everyday life. (Coincidentally, I've been reading his book on Bill Gates' recommendation.)

His numbers were not far off from my own. I found that it took 0.11 kilowatt-hours to boil water in the electric kettle. Boiling one liter of water on the gas stove took about eight minutes. I found an estimate for my stove's BTU per-hour rating, did the math, and found that it uses an estimated 0.35 kilowatt-hours.

Does that make it a clear winner? No! It turns out that centralized power plants are about 33 percent efficient, according to the U.S. Energy Information Association. Then a few percent of the energy from burning fossil fuels is lost in sending electricity over transmission lines.

Taking electricity generation and distribution into account means that the two methods are roughly equal in terms of the amount of energy required, concludes MacKay.

Cleverly, he suggests that people take advantage of the fact that gas burners are only 37 percent efficient at converting energy from the gas flame to heating the water. Hey, you can use that gas burner to help heat the room!

The people at efficiency start-up PlotWatt also concluded that gas is a good way to go, particularly if you live in an area that is powered by coal.

But on a warm day, an electric kettle's insulated design keeps the heat contained and is a good choice, MacKay says.

Having on-site clean electricity does tilt things in favor of the electric kettle. You use less energy overall and you eliminate that waste from centralized power generation and delivery. Given that we're producing more electricity than we consume at this time of year, we're going with the kettle. Plus, it's hot outside.

Clearly, there are many other more significant ways to save energy at home in normal circumstances. But as we wait out the repairs to the water system, it's good to know, one day later, that we've thought this one through.