What exploded? Oh, you just dropped your steel water bottle

Instead, she started with a clang.

The 22-year-old aspiring physician assistant walked into her classroom juggling a backpack, medical equipment and lunch. She also toted her Hydro Flask, a stainless-steel water bottle she has brought nearly everywhere since acquiring it during undergraduate studies.

As she swung her backpack around to sit down, the Hydro Flask slipped out of a side pocket and fell to the hard floor, making itself noisily known.

“The whole classroom just looks at me, because—one—I look like a pack mule with all my bags," Ms. Hoffmeyer says. “Then, to top it all off, my Hydro Flask is making this huge clanking as it rolls away."

Large reusable stainless-steel water bottles, such as the ones made by Helen of Troy Ltd.’s Hydro Flask and Simple Modern, are nearly everywhere, including offices, gyms and college campuses.

The bottles let users cut back on single-use plastics and are typically insulated to keep beverages chilled.

And they are loud when they hit the deck.

Ms. Hoffmeyer apologized to the class before scrambling to retrieve her yellow bottle. “On the bright side," she said, “they also know that I am a sustainable queen, and I use a reusable water bottle."

In the silent waiting room of a walk-in clinic, Sarah Luxton once watched her bottle slip out of her bag—seemingly in slow motion—and crash to the floor. The 23-year-old student in Ontario, Canada, says her Hydro Flask is like a third leg, attached at her hip at all times.

Embarrassed, she scrambled after it as its clanging scared everyone in the room. “It’s the kind of thing you just hope that no one sees or hears," Ms. Luxton says. “But of course everyone sees and hears it. How could you not when they’re so loud?"

Mike Beckham, chief executive of Simple Modern, describes the sound of his companies’ bottles dropping as a distinctive high-pitched “ting." The company monitors reviews and customer-service complaints but doesn’t often see ones regarding noise, he says. “Most people understand—they’re just super loud."

Metal water bottles have become so popular on college campuses that Peter Ubertaccio, vice president for academic affairs at Caldwell University, says he considers them part of a uniform: “You get so used to them falling."

Teachers have vented online about bottle noise in an online thread titled “Can we talk about Hydroflasks and the like?" on the Reddit forum.

“Is anyone else tired of hearing loud metal clanging against the floor everyday?" one Redditor wrote. “I understand they’re much better for our environment but holy cow. Carpeted-classroom teachers, I envy you."

Eliza Richardson Marone, an associate teaching professor of geoscience at Pennsylvania State University, has taught classes in theater-style lecture halls that cause dropped water bottles to roll down toward the front. “That’s always kind of funny," she says, “watching students scramble to go get them."

Hydro Flask embraces its classroom-disrupting powers. “During the pandemic, we also missed the sound of our Hydro Flask bottles rolling down the aisle in a silent lecture hall," says Hydro Flask Director of Marketing Yiorgos Makris, “and we were thrilled when students were able to safely return to class."

Jatin Chowdhury, a 25-year-old electrical engineer, studied the sounds that metal water bottles emit as part of a Stanford University team of graduate students.

The team wrote in the published findings of their research: “Although water bottles are not designed to function primarily as musical instruments, the authors have noticed that certain bottles produce a pleasing resonant sound when struck with a mallet, knuckle, or other body part."

The most surprising research finding, Mr. Chowdhury says, was just how complex an acoustic system an insulated water bottle can be. The bottle’s size will affect the frequency of sound waves inside of it, he says, so smaller bottles make more of a “ding," while larger ones make more of a “gong."

Bottles made of cheaper materials have more molecular impurities that cause the sound waves traveling through space to lose energy, deadening the sounds. More-expensive homogeneous materials allow the sound waves to “ring out" for a longer period, Mr. Chowdhury says.

Fallen bottles full—or partially full—of water will have an “almost-bouncing sound," he says, as the water sloshes inside.

The Wall Street Journal dropped a sampling of bottles—Hydro Flask, Klean Kanteen, Laken and h2go—and recorded the results, ranging from a hollow resonant sound to a loud metallic clang.

“Though we certainly don’t encourage dropping our bottles," says Hydro Flask’s Mr. Makris. “We encourage you to give it a gentle tap at different water levels. For the musically inclined, it can spur some creativity or for students it’s simply the Pavlovian bell of learning."

The ring of a dropped Klean Kanteen bottle, says a spokeswoman for the company, is “that sweet sound when sustainable recycled materials hit Mother Earth."

H2go didn’t respond to requests for comment. Automated responses from Laken said the company is closed for summer holidays.

The dropped-bottle impact can go beyond the auditory, Dr. Saylee Tulpule found. A patient came to the podiatrist in the greater Washington, D.C., area, in recent weeks after dropping a water bottle on a foot at the gym. Luckily, the patient’s foot was only bruised.

Shawn McEntyre, a 38-year-old video producer, says his most embarrassing drop occurred in 2019 while manning the AV booth in Utah for a companywide presentation. The room was silent, save for the presenter.

The silence was shattered when, alone in the booth, he knocked his bottle onto a stack of metal chairs. “Everyone turned around and was looking at me," he says. “I even got a shout-out from the guy giving the presentation."

After another drop, in Mr. McEntyre’s kitchen, his two cats sprinted out, fear-stricken. He tweeted:

“The floors quake, animals of all species run for their lives, children begin to cry adults jump from pure fear and terror, the impact is deafening."

“I dropped my hydro flask."

This story has been published from a wire agency feed without modifications to the text.