Hold your canteen under a natural spring and come away with crystal-clear water, potentially brimming with beneficial bacteria and minerals from the Earth.
That's what proponents of the "raw water" movement are banking on - the idea that drinking water contains the things nature intended without chemicals such as chlorine, often used in urban water treatment.
In some areas, including the West Coast, water captured in glass bottles and sold straight to you has become a high-dollar commodity.
But by shunning water safety practices, experts warn, the purveyors also might be selling you dangerous bacteria, viruses and parasites that can make you sick.
"We're glad people are so interested in water quality and the value they're placing in safe water," said Vince Hill, who heads the Waterborne Disease Prevention Branch at the U.S. Centers for Disease Control and Prevention. "But I think it's also important for people to know where their water comes from, what's in it, how it's delivered and whether it's safe to drink."
Water quality long has been debated. Could demineralized water be bad for you? What about plastic bottles? And do some water systems have dangerous levels of lead? Many communities won't add fluoride to drinking water, though it strengthens teeth and is safe at low doses.
But all in all, the U.S. has "an incredibly safe and reliable water supply," said David Jones, professor of history of medicine at Harvard Medical School.
Federal law requires the U.S. Environmental Protection Agency to set standards to ensure that tap water is safe to drink. The Food and Drug Administration regulates water that is bottled and sold.
But raw water is up to you.
"In some respects," Jones said, "the fact that people are worried filtration is removing necessary minerals is really an extreme case of one of these First World problems."
Experts say raw water may contain minerals, but you can get the minerals you need from a healthy diet - and the risk of harmful bacteria, viruses and parasites is not worth any benefit from trace minerals.
Truly raw water, simply hydrogen and oxygen, is fine to drink as long as it's clean, said Michelle Francl, chairwoman of the chemistry department at Bryn Mawr College in Pennsylvania.
"Water pulled from a spring or water that comes out of the tap - the water molecules are identical," she said. "So the only difference is what else is in there. And some of those things might be innocuous, like the minerals. Some of them might be not so innocuous. Things like giardia and bacteria have been found in springs."
That's why it's imperative to know exactly what you're drinking. Water cleanliness depends on things you can't see - whether herds of elk or moose relieved themselves in a stream and left it full of parasites, or whether groundwater has been contaminated by arsenic, radon or uranium, or by agricultural pesticides, herbicides and other chemicals.
"The lack of clean water kills hundreds of thousands of children a year," said Francl, who is also a scholar at the Vatican Observatory. "So this notion of raw water is crazy."
Water is treated to remove harmful bacteria such as E. coli, salmonella and giardia, a common parasite that causes a diarrheal illness called giardiasis and can be contracted by drinking "untreated or improperly treated water from lakes, streams, or wells," among other ways, according to the CDC.
In the late 19th century, in response to epidemics of cholera, a bacterial disease that spreads in water, cities made massive investments in water treatment processes, including sand filtration, said Jones, at Harvard Medical School.
Once communities could separate sewage from drinking water, then filter that drinking water, cholera nearly disappeared from Western Europe and North America.
"These kinds of changes are likely largely responsible for huge improvements in human life expectancy," which rose by about 30 years from 1900 to 1970, Jones said.
"Clean water has made such a difference in people's life expectancies in the United States and other industrialized countries," Francl said, "so I can't imagine why you would want to drink water that wasn't and thereby endanger your health."
Doug Evans said he subsists on an organic, plant-based diet and has been drinking raw water for nearly two decades.
"If you have heavily processed water with chemicals in it that are designed to kill bacteria, then I think it can really materially alter the body," he said. "The springs that I will drink from have all been tested. And the closer you're drinking it to the source, the safer it is. So I think that if you're drinking from a natural spring at the source, it tastes better. And I feel good drinking it."
Evans, who founded the now-defunct juicing company Juicero, said that when he can't get his own water, he buys it from Live Water, a raw water business based in Oregon.
The company website says "all other bottled, filtered, tap, and even spring waters are sterilized with ozone gas, irradiated with UV light, and passed through a submicron filter," and "blasting water with ozone changes its molecular structure."
Live Water did not immediately respond to requests for comment.
Francl, the chemist, said ozone gas is used to remove bacteria and other things from water, and then the ozonized contaminants are strained out, leaving clean water.
Ozone does not change water's molecular structure, she said. If it did, it would no longer be considered water.
Evans said, "You want to drink tap water, drink tap water. You want to go buy water that's been filtered and put in a plastic bottle, I think that has environmental consequences, but I'm not going to protest.
"The pundits will say water is H2O, but I think as you break it down, there's a lot more to it. And I feel very vibrant on its consumption."