Many of us use water thoughtlessly; it seems as abundant as the air we breathe and a free swig is available almost anywhere. But fresh, potable water is already a precious commodity in many drier parts of the world, and as it grows rarer—and thus, dearer—in developed countries, the true value of H2O is beginning to seep in.

Until water shortages impact more of us directly it is likely that this liquid resource will continue to be poorly managed. Whether it's the inefficient flooding of farm fields or hosing down our cars every weekend, people find many ways to waste water.

The recent story of a profligate user who changed his ways could perhaps serve as an example for us all: Saving water often comes down to paying attention. Although Atlanta recently suffered its worst drought in a century, the local estate of wealthy investor Chris G. Carlos consumed 440,000 gallons (1.67 million liters) in September 2007 alone. After a public outcry, Carlos dramatically reduced his monthly usage to just 12,000 (45,400 liters)—about what an average U.S. family of four expends during the same time period.

Although that's an extreme case, it shows that there's often little reason why we can't save more water in our day-to-day lives. Here's a list of some of the more egregious ways in which we squander it; some are easily avoidable, whereas others will require big changes in agricultural and industrial practices.

1. Doing the Dishes: By Hand or Dishwasher?

A lot depends on your dishwashing style: A typical session that includes turning the water on and off will go through about 20 gallons (75 liters) or so. But if you leave the water running while scraping at those last grisly bits on your fine china, you may use more than twice that amount. Modern electric dishwashers, in contrast, need less than 10 gallons (38 liters) per average load, says a survey by the American Water Works Association.

2. Washing the Car (and the Driveway)

Wear that bathing suit at the pool or the beach, but not for posing in the driveway while sluicing the suds off your auto with hose water. According to Kaady Car Washes, a west coast chain, a home car wash can go through 80 to 140 gallons (300 to 530 liters) of water, whereas a wash at one of its garages will take about 30 to 45 gallons (115 to 170 liters). Professional car washes also utilize methods that recycle water: The U.S. Environmental Protection Agency mandates that wastewater be channeled to treatment plants to avoid polluting the environment; contaminated water from your home car cleansing just flows into street drains or leaches into the soil.

3. Slipping Through the (Pool) Cracks

Cannonballs aside, a swimming pool naturally loses about 1,000 gallons (3,785 liters) a month to evaporation, according to the Maui County, Hawaii, Department of Water Supply, although the local climate and the pool's overall surface area determines the amount that's actually lost. A bigger problem arises from the leaks that pools often develop during their lifetimes from cracks in their foundations, liner tears and pipe damage. Estimates vary wildly, depending on everything from a region's temperature fluctuations to seismic activity. National Leak Detection (pdf), a company based in Mesa, Ariz., puts the figure at a whopping 30 percent. Three hundred miles (480 kilometers) west in Palm Springs, Calif., American Leak Detection, Inc., puts the pool leak rate at a more conservative one in 20. Either way, because most pools have automatic refillers, owners often fail to notice the loss until their next water bill arrives.

4. Lawn Sprinklers: Fountains of Backyard Verdure or Pernicious Aquifer Guzzlers?

The water sprinklers that keep the turf lush and the flowers blooming can consume 265 gallons (1,000 liters) an hour, says Waterwise, a U.K. water-conservation group. This amount rivals or exceeds estimates of what an average U.S. household uses daily. A good tip: deploy the sprinkler either in the early morning hours or at dusk; less water will evaporate in the cooler temperatures and more will actually get to the plant roots. But be mindful about leaving it on; besides potentially drowning your petunias, you may also be breaking the law. A new drought-busting measure in the City of Los Angeles will permit automated sprinklers to run only 15 minutes a day this summer.

5. Well-Watered Desert Resorts

The term "desert resort" is synonymous with the City of Las Vegas. The Venetian canals of the Bellagio, as well as the Mirage's water-and-fire volcano, make conspicuous water consumption in Sin City iconic. Appearances can be deceiving, though. In fact, the Las Vegas Strip accounts for just three percent of local water use, according to the Southern Nevada Water Authority. Fully 70 percent of the city's water supply goes toward irrigating the 60-plus golf courses and the many residential lawns in the area. The municipal government has, however, taken steps to scale back on the city's greenery, for example, by cutting the maximum size of a domestic lawn to just a backyard patch. Nevertheless, keeping grass verdant in the middle of the desert is arguably folly in the first place.

6. Biofuels' Hidden Downside

Biofuels typically burn cleaner than fossil fuels and therefore emit less carbon dioxide into the air. But plant-power sucks up ridiculously large quantities of water compared with oil and natural gas production. A study (pdf) presented at an American Society of Mechanical Engineers conference in 2007 offers some alarming estimates: Producing a gallon (3.79 liters) of corn ethanol, for example, consumes 170 gallons (644 liters) of water in total, from irrigation to final processing. Soybean biodiesel manufacture needs some 900 gallons of water (3,400 liters) per gallon of fuel. On the other hand, the water requirement to make a gallon of regular gasoline is just five gallons (19 liters).

7. Agriculture in the Arid Southwest

Much of the U.S. Southwest is a desert—at least it was at one time in the past. But about 90 percent of the Colorado River's water is today diverted into these parched lands for agricultural irrigation. Perhaps half of this regional resource does not even reach the intended crops because it is lost to evaporation and seepage during pumping and transport, according to a 1997 Cornell University study that appeared in the journal BioScience. Many farmers rely on flood irrigation, which, though inexpensive, is a highly inefficient means of delivering water to thirsty plants. The Colorado's dwindling water flow threatens the supplies of seven states and has spawned a plethora of lawsuits regarding water rights. As our featured article on water points out, shaving irrigation water by 10 percent would save more than is used by all other water consumers put together. A prime example of this ill-advised approach is growing alfalfa in the desert.

8. Alfalfa Farming Woes

Many think of alfalfa mainly in terms of the sprouts that end up on sandwiches, but the vast majority of the nation's alfalfa output feeds livestock. The relatively low-value crop uses up about a quarter of California's irrigation water but contributes only 4 percent to the state's total farm revenue, according to the Natural Resources Defense Council. It's not that alfalfa itself consumes more water than other farm plants, says Mark Grismer, a professor of agricultural engineering at the University of California, Davis; farmers grow alfalfa year-round in what is essentially a desert climate in the southwestern U.S.

9. The Ruin of the Aral Sea

The Aral Sea in central Asia was once the fourth largest body of freshwater on the planet. But by siphoning off waters from the massive lake for irrigation, local farmers and governments in Uzbekistan and Kazakhstan have drained the Aral Sea to 10 percent of its former size. (Satellite images show the sea's shrinkage over several decades.) The Aral has split into three parts, two of which are so salty that all the fish in them died. Lake Victoria in eastern Africa is another victim of overuse. Its water level is half of what it once was.

10. Wasting Water by Getting "Wasted"

As refreshing and cooling as that beer may taste, it's likely to leave you less hydrated than you were before you started. Alcohol is a diuretic, which means it increases the frequency of urination (but you knew that already). Alcohol suppresses an antidiuretic hormone called vasopressin that tells our kidneys to reabsorb and conserve water. The more you drink, the more the hormone level falls, and thus the more water you lose. Severe dehydration is a big reason why after a hard night out, you end up with a hangover the next day.

How do you try to limit your water use? And how have you wasted water in the past? Let Scientific American know in the comments area below.