The Green Lantern

Bathing Hot, Hot, Hot

How bad should I feel about taking hot showers?

I know that taking long, hot showers is an environmental no-no. But now that the weather’s getting colder, I just can’t face the day without one. Exactly how much damage am I doing to the planet?

Guilt is a tricky thing to quantify. In the grand scheme of things, a hot shower represents just a fraction of your overall water and energy usage. And the Lantern will admit that she, too, needs the promise of a few steamy, soapy minutes to rouse herself out of bed on a frigid morning. But that doesn’t mean that she condones epic showers.

How short should your hot showers last?

Let’s take a closer look at the numbers. In a 1999 study of nearly 1,200 single-family homes, showers used an estimated 11.6 gallons per person per day, or roughly 17 percent of all indoor water consumption. (Toilets were no. 1, at 27 percent, and then washing machines, at 22 percent.)

How much water your personal ablutions require depends on what kind of showerhead you have and how long you luxuriate beneath it. The nonprofit Alliance for Water Efficiency has a nifty chart that can help you estimate exactly how much your daily shower sends down the drain. According to the Alliance, 25 gallons or less constitutes water-efficient bathing: That’s five minutes with a 5-gallon-per-minute showerhead, or 12 minutes with a 2-gallon-per-minute showerhead. (Since 1992, federal regulations limit all new showerheads to a maximum flow rate of 2.5 gallons per minute.)

Hot showers require more water than cold showers, because of the extra time spent waiting for the flow to heat up. According to a preliminary analysis from a researcher at Lawrence Berkeley National Laboratory, an average of 5.21 gallons per household, per day spirals down the drain before anyone even starts bathing.

So what does that mean in the big picture? As we discussed a few months ago vis-à-vis toilets, what flows out of your faucets and showerheads is only part of your overall water footprint. The average household uses far more water outdoors than indoors—and your home’s total consumption is going to be dwarfed by the production of all the goods you consume, which raises each American’s daily footprint to about 1,800 gallons. (Mother Jones recently noted that it takes 33 gallons of water to produce a 16-ounce Diet Coke—about as much as a reasonable 13-minute shower under a 2.5 gpm showerhead.)

If you don’t live in an area where droughts are a pressing concern, there’s still the energy issue. No matter how hot or cold you like it, your shower is going to have an energy footprint. After all, it takes energy to treat and deliver potable water to your house, and once your shower water goes down the drain, it has to be treated all over again before it’s released back into the environment.

Cranking up the temperature, however, will significantly increase your energy costs. Overall, water heating can account for up to 25 percent of your home’s energy use, and showers use 37 percent of the hot water in the average home. (Add in baths, and it rises to roughly half.)

How much energy will a single hot shower set you back? It depends on a bunch of variables, but let’s assume you’re taking one of those 25-gallon showers and that the water is 55 degrees when it enters your heater (a reasonable average of seasonal temperatures around the nation). It takes 8.3 British thermal units to raise the temperature of one gallon of water 1 degree Fahrenheit, and a hot shower is usually 105 degrees. Et voila, getting your shower nice and steamy under these conditions will require 10,375 Btus of energy.

Next, you have to consider your water heater’s energy factor. This is an overall rating—expressed as a number from zero to one—that indicates how efficiently the machine converts the energy it receives into hot water available for your use. (The higher the number, the more efficient the machine.) The typical gas heater has an energy factor of around 0.6, so you’d need about 17,000 Btus of gas input to warm your shower. If you used a typical electric water heater, with an energy factor of around 0.9, the same shower would consume 12,000 Btus of electricity.   There’s a big caveat here: Every Btu of electricity delivered to your home requires roughly three Btus’ worth of primary fuel at the power plant, raising the total energy cost of your electrically heated shower to about 36,000 Btus. (There’s some loss of energy when gas is delivered to your home, but it’s much less significant.)

In 2005, the average American consumed about 200,000 Btus of residential energy every day (PDF). When you factor in all of our various energy costs, including transportation and the production of goods, per capita consumption rises to a little more than 900,000 Btus.

So what are you supposed to do with all those numbers? In the end, the Lantern suggests a commonsense approach to your morning ritual. Take the hot shower if you need it, but keep your time to a minimum. Avoid shaving or brushing your teeth in the shower, unless you’re willing to shut the water off while you’re doing it. (Look into installing a lathering valve, a showerhead attachment that allows you to shut off the flow while keeping water temperature constant—though note that they’re not recommended for all households.) If you don’t have one already, check to see if your municipality offers rebates for installing low-flow showerheads or those that automatically slow water flow to a trickle once the water has reached a comfortably hot temperature. The Department of Energy also has tips on how to make sure your water heater is operating as efficiently as possible.

Finally, fix your drips: The 1999 water-usage study found that leaks wasted 9.5 gallons a day, per person—almost as much as showers.

Is there an environmental quandary that’s been keeping you up at night? Send it to, and check this space every Tuesday.