“What percentage of the Earth is covered in water?” a woman in Calistoga asked Wednesday as she tossed a blue globe into the air.

She could hardly keep up with the shouts of Calistoga Elementary School fourth-graders wagging their hands in the air.

“Seven million billion?” asked one fourth-grader.

“No,” the Project WET volunteer explained, exchanging a look of amusement with another volunteer. “It can’t be more than 100.”

She wasn’t about to give the kids an easy answer. She was going to make them work for it.

Students gathered in a circle around her as she explained the rules of the experiment. They were to toss the globe around the circle, counting how many times their thumbs landed on water. After enough time, statistically, this should give them a rough estimate of how much water covers the Earth.

The Project WET water education festival in Calistoga engaged 185 Calistoga Elementary fourth- and fifth-graders in this and similar activities designed to promote environmental stewardship and water conservation. The Calistoga event was part of a nationwide program reaching more than 50,000 students across the U.S.

The event was planned for last week, but was rescheduled due to rain.

With support from Nestle Waters North America and its local brand, Calistoga Mineral Water, the event marks the sixth consecutive year and eighth out of the last 10 that Calistoga Beverage Company has hosted Project WET.

“Kids look forward to it every year,” said Vicki Spitzack, factory manager for Calistoga Mineral Water Company. “It opens their eyes. We hope they will be like sponges and soak up what they learn today.”

A nearby volunteer chuckled at the metaphor, but nodded in agreement.

“We want to teach them to be environmentally responsible,” said Spitzack, noting that fifth-graders who participate in the program for a second year often remember what they learned in fourth grade. “We’re pretty sure it resonates with them.”

Said local coordinator Ben Page, “Kids seem to get a kick out of it.” And they’re not just having fun, he said. They’re learning science. Project WET curriculum meets standards set by the No Child Left Behind Act, with hands-on activities touching on topics such as turbidity and life cycles.

“This is what I wanted to do as a kid,” said Page, “and it’s how I ended up working in the lab at Nestle Waters.”

Fourth-grader Yadira Guzman can’t wait to come back next year. “We learned about the water cycle,” she said, “how many waters there are, the life cycle, and how to help the community not to, like, be bad.”

Dyan Zarate, also in fourth grade, said the festival encouraged her to be more careful about conserving water. She wants to pay more attention to turning off the faucet, and she wants to teach her parents, too.

“I want to take care of water,” she said, “and I want to take care of the world.”

Working up a sweat from all of the activities and experiments, each student was given a token on behalf of the sponsor: their own bottle of Calistoga mineral water.

By the way, about 70 percent of the Earth’s surface is covered by water.