Kauss and her contemporaries struck at the right time. The importance of fitness and wellness were starting to gain a foothold in fashionable crowds, and concerns over consumer waste and plastic’s potential to leach chemicals into food and water were gaining wider attention. People wanted cute workout gear, and they wanted to drink water out of materials other than plastic. Researchers have found that the chance to be conspicuously sustainability-conscious motivates consumers, especially when the product being purchased costs more than its less-green counterparts.

Nearly a decade on, the water-bottle trend shows no signs of slowing, and people just seem to like their fancy bottles a lot. The insulated metal variety, the most popular, does a far better job than plastic of keeping beverages at ideal temperatures. They’re durable and useful. When I put out a call for opinions on Twitter, I heard from hundreds of people about how much they loved theirs. Rebecca Thomas, a 28-year-old in Atlanta who owns three S’wells, says she once paid a ransom to an Uber driver after she left one behind in the car. (“That’s when I decided I’d never put wine in one again,” she says.) Others were similarly dedicated. “I will be buried with all of my different sizes of Hydro Flask,” says Elizabeth Sile, an editor in New York City. “Maybe by then Hydro Flask will come out with a coffin, so I can be buried in that, too.”

The trend’s Instagram visibility might make it seem like high-end water bottles are the sole province of women. Indeed, brands such as bkr, whose bottles are pastel glass and can come with a special top meant to hold lip gloss, are explicitly marketed as products of feminine beauty. (Drinking water, after all, is often lauded as the ultimate skin-care product.) But the category’s origins in camping gear mean that it started out with a strong foothold among male Millennials as well, and brands such as Yeti and Hydro Flask have continued to court a more masculine audience. Mike Ferguson, a 37-year-old in Los Angeles, has four Yetis of various sizes that he usually uses for iced coffee and water. “I have very few vices, but this is one,” he says. “Am I a brand loyalist? I don’t think so, but the evidence suggests otherwise.”

Ferguson, like many other people I spoke with, got his first Yeti as a gift. Kauss says that’s a trend she sees with S’well’s customers, too: People will buy one or two, presumably for themselves, and then come back to the website around the holidays and buy six. Most brands also customize orders for large corporate clients, meaning your employer might hand you a logo bottle at the end of the year. Even if spending 40 or 50 bucks on a water bottle sounds bad, getting one for free can turn reluctant consumers into evangelists.

When those factors are taken together, it’s hard to be surprised that so many $50 water bottles exist, or that people have snapped them up in droves. On a certain level, a nice water bottle fulfills its promise in the way few things do. They hold water. They stay cold. They look nice on your desk. They don’t leave an unsightly sweat ring on your nightstand. For people such as Mongeon, the art teacher, they look like things that are owned by people who know what they’re doing. For a lot of people, they spark a little bit of joy in the otherwise mundane routine of work, exercise, and personal hygiene. For a generation with less expendable income than its parents’, a nice bottle pays for itself with a month of consistent use and lets you feel like you’re being proactive about your health and the environment.