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Volunteers load up rain barrels, sold at a discounted price to San Mateo County residents Saturday, in hopes of saving thousands of gallons of water.

Dennis Payne of Redwood City bought three rain barrels Saturday from a discounted program for county residents, in hopes of saving water for his tomatoes, melons, squash and potatoes.

Emotions ran high at the big rain barrel sale that took place under sunny skies in San Carlos on Saturday, where hope was in greater supply than raindrops.

Hundreds of San Mateo County residents swung by a bayside parking lot to pick up nearly 400 of the 50-gallon barrels made of recycled plastic that they had reserved online at the discounted price of $30 apiece — including a $50 rebate — from the City/County Association of Government and its FlowstoBay.org clean water program.

“We’re just really hopeful we’ll get some rain to water our plants,” said Michael Sage of Pacifica (where sunshine is predicted all week) as he waited in a line of cars so that volunteers could load his barrel into his trunk.

Paola Flygare of Burlingame (sunshine predicted all week) hadn’t reserved a rain barrel but noticed the line of cars as she bought mulch next door. She hurried over in hopes of snagging one. Flygare was supposed to be on a plane to Tahiti with her husband on Saturday but they canceled, fearful of the coronavirus’ fast-spreading omicron variant.

“Getting a rain barrel would be a good consolation prize!” she laughed. “Hopefully, hopefully!”

The county’s water experts say the best time to get a rain barrel is now, regardless of the weather. The Bay Area typically receives 18 to 23 inches of rain a year, and a rain barrel positioned beneath a home’s downspout can collect — get ready for some math — 312 gallons of water for every half inch of rain that falls on a 1,000-square-foot roof, said Suzi Senna, the Flows to Bay program’s representative, checking details on the web as volunteers whisked barrels into car trunks around her.

Volunteers Ulla Foehr and Alex Rinear, Reid Bogert of the City/County Association of Governments of San Mateo County, Suzi Senna of the association’s Flow to Bay program, and volunteer Jesse Craft gather behind some of the 396 rain barrels they loaded into the cars of county residents who bought them Saturday at discounted prices.

Put another way, 150 rain barrels can save 18,000 gallons of water, said Reid Bogert of the City/County Association of Government, who brought his 5-year-old son, Yvo, to help set things up. Between today’s sale and one in November, he said, San Mateo residents now have 700 barrels — and are poised to save 84,600 gallons of water, give or take.

Kat Thomas of Brisbane (sunshine predicted all week) hopes to collect rain for her peach, pear and plum trees, as well as the grapevines she’s just planted. Although 2022 got off to a wet start, even Thomas’ cactuses looked shriveled before that, after two of the state’s driest years.

So why not just turn on the garden hose?

“Maybe it’s guilt,” Thomas said. “It just sort of feels wasteful. You hear of people having to travel miles for drinking water, and we’re using pure, clean water to water plants and flush the toilet.”

When it comes to choosing between a $30 rain barrel or a garbage can for half the price to collect your rainwater, Bogert of the county said you get what you pay for.

For one thing, the top of the barrel has a screen to keep out debris — and especially mosquitos, which can carry disease, he said. The barrel is also equipped with a spout at the bottom to drain the water into a bucket or watering can. There’s another spout at the top for overflow, or to attach a second barrel — a process called daisy-chaining, Bogert said. The connector for that is included in the price.

Reid Bogert of the City/County Association of Governments points out the drain features of the rain barrels his agency is selling at a discounted price to San Mateo County residents to save water.

Maybe the trickiest thing about getting a rain barrel is setting it up.

“You have to hacksaw your downspout,” Bogert said. The opening to a downspout hovers just above the ground. But a barrel is 3.5 feet high.

“Really? I hadn’t considered that,” said Flygare, as she hung around to find out if there would be any barrels left over she could buy.

Of the 396 rain barrels reserved online for pickup, 388 of them had been picked up by 11:50 a.m. With eight barrels remaining and the sale ending at noon, that left 10 more minutes of uncertainty. And some people, like Dennis Payne of Redwood City (sunshine predicted all week), were buying more than one.

Payne had loaded three into his Volvo SUV, planning to water his family’s tomatoes, melons, spinach and potatoes. He also hoped to buy more at the next sale. “We have five downspouts,” he said.

Flygare said she still wanted a barrel, despite the hacksaw problem. Her husband wandered by and called out that he’d be happy to hack as many downspouts as she liked.

Five minutes ticked by. No more cars pulled in, but four people called to say they were late and to ask Senna, of Flows to Bay, to set their barrels aside, which she did.

“Congratulations!” Senna told Flygare. She had a rain barrel.

It’s not Tahiti, Flygare said. “But I’m really happy.”

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov

Nanette covers California's public universities - the University of California and California State University - as well as community colleges and private universities. She's written about sexual misconduct at UC and Stanford, the precarious state of accreditation at City College of San Francisco, and what happens when the UC Berkeley student government discovers a gay rights opponent in its midst. She has exposed a private art college where students rack up massive levels of debt (one student's topped $400k), and covered audits peering into UC finances, education lawsuits and countless student protests. But writing about higher education also means getting a look at the brainy creations of students and faculty: Robotic suits that help paralyzed people walk. Online collections of folk songs going back hundreds of years. And innovations touching on everything from virtual reality to baseball. Nanette is also covering the COVID-19 pandemic and served as health editor during the first six months of the crisis, which quickly ended her brief tenure as interim investigations editor. Previously, Nanette covered K-12 education. Her stories led to changes in charter school laws, prompted a ban on Scientology in California public schools, and exposed cheating and censorship in testing. A past president of the Society of Professional Journalists' Northern California chapter, Nanette has a master's degree in journalism from Columbia University and a B.A. in sociology from Queens College. She speaks English and Spanish.