Carrie Frost is well equipped for hydration. A registered nurse and a mother of two from Colorado, she estimates that her family has accumulated “upward of 25 to 30” reusable flasks at home for keeping cold drinks: flasks large and small, of various designs and colors, with a straw and without. But last month, as she sat in 90-degree heat at her son’s travel baseball tournament, she drank from a plastic water bottle that she had purchased for $3 at a local grocery store.

“Convenience,” she said, laughing, as she tried to piece together why, once again, she was not using one of her many beverage containers. “I guess we’re just a lazy society.”

Americans are drinking a lot of water, but they are on the fence about how best to do it. More than $2 billion in reusable water bottles were sold in the United States in 2022, up from around $1.5 billion in 2020, according to Greg Williamson, the president of CamelBak, which is a maker of reusable bottles.

And sales of single-serving water bottles have been rising steadily, too, reaching 11.3 billion gallons in 2022, according to the most recent data from the Beverage Marketing Association, which tracks beverage sales.

In other words, consumers are spending billions of dollars a year on reusable bottles to stay hydrated and then buying bottled water anyway, even as faucet water remains free.

“Faucet?” said Jason Taylor from Georgia, whose son was playing the same Birmingham baseball tournament. “Faucet? I haven’t drunk from the faucet since I was 18.” He had heard stories about tainted water, like in Flint, Mich., and did not trust the faucet water at the hotel, he said, so he filled his reusable flask with ice from the hotel and poured bottled water over it. The hotel ice he trusted; the faucet water there, not so much.

Beverage consumption is in a fluid period. Americans are moving away from empty sugar calories but are still hooked on the convenience of a chilled plastic bottle from the corner-store fridge. So we are amassing containers, single-use and reusable, in kitchen cabinets and landfills alike.

Sales of reusable water bottles “are absolutely skyrocketing,” said Jessica Heiges, a sustainability consultant based in Berkeley, Calif., where she recently completed a Ph.D. in the creation of waste-free systems. But, she added, people who fill their reusable flasks with water from a bottle have not fully embraced the environmental proposition.

“They are not all the way there or are not fully convinced,” Dr. Heiges said. And, she noted, reusable water bottles take resources to make, so having too many isn’t great for the environment, either. “You can find them at every Goodwill and Salvation Army. People are overflowing with them.”

Alaina Waldrop, in Birmingham, has around 20 water bottles, as precious to her as purses, she said: “You have a decent water bottle and you get sick of it, or you’re used to seeing it all the time, and find a new one that’s pretty or it’s a new color or it holds more water or fits in a cup holder better.”

Ms. Waldrop, 20, works at Dick’s Sporting Goods, about a mile from Birmingham’s baseball fields. The store has multiple displays of reusable flasks, featuring major brands like Yeti and Hydro Flask. A display of Stanley flasks ($45 each) came with a sign: limit four per customer. “They’re so popular,” Ms. Waldrop said. “I bought one for my mom and one for my sister. We’re all water-bottle freaks. We all have this obsession. I wish it made more sense but it doesn’t.”

She tends to fill her bottles at home with filtered water but doesn’t trust faucets on the go, so she buys single-serving bottles at the gas station or convenience store and pours that water into her reusable container. “I drink whatever is in the plastic and then I throw the plastic away,” she said with a laugh. Why not simply drink all the water from the plastic bottle she just purchased? “It doesn’t stay cold for as long,” she said.

In practice, there may be little difference in quality or safety between bottled water and tap water, said Ronnie Levin, an instructor and expert in American public drinking water at the Harvard T. H. Chan School of Public Health. “It’s often just some random tap filling those water bottles,” Ms. Levin said. “Monitoring of bottled water is somewhere between zero and not routine.”

When putting bottled water in the flask, “you’re not necessarily getting anything better, except that you’re now polluting the environment.”

In the baking heat at the baseball fields, a line had formed at a snack shack that sold water for $3 and charged $2 for ice in a Styrofoam cup. Steps away was a refillable filtered-water tap that was used by some people but had no line. Maybe that’s because the filtered tap was free.

Water has become popular enough that it is often as or more expensive than soda, despite having less substance — in the form of sugar — to offer. At a handful of nearby convenience stores, the prices of water and soda were neck and neck; at Walgreens, bottles of Dr Pepper and other sodas sold at $4 for two, as did bottles of Dasani and Aquafina water.

Michael Bellas, the chairman and chief executive of the Beverage Marketing Company, said that bottled water remained far less expensive if purchased in bulk, at Costco, say, or the supermarket. But prices rise sharply for single-serving bottles when the retailer has a thirsty audience on the go, he noted.

“The airports just soak you,” Mr. Bellas said.

At the Hudson store at the Birmingham airport, 20-ounce bottles of Dasani water and Smartwater (both owned by the Coca-Cola Company) cost $4.29 with tax, while all the 20-ounce sodas (Coca-Cola, Diet Coke, Sprite) cost $4.09.

“Everyone has to hydrate, and people think it makes their skin look nice,” Kim Shoemaker, a Hudson employee, said of water. “No sugar, no chemicals, no additives.” Ms. Shoemaker, 60, said she bought cases of water at Costco and kept single-serving bottles in every room of her home, but also owned many reusable flasks. “Oh, my gosh, probably about six,” she said. “I don’t use them. I don’t know why.”

Just outside the Hudson store was a water dispenser for reusable containers, its water filtered and free of charge and mostly going unused.

Out at the baseball fields, Ms. Frost, who had traveled from Colorado for the tournament, said she had family members who didn’t understand why a person would spend on a reusable water container and single-serving water bottles and not just fill a cup from the tap.

“Ask my husband,” she offered. “He thinks it’s the stupidest thing in the world.”

To which her husband, Spencer Frost, gruffly added: “Just drink from the hose.”