Doniece Sandoval has seen the popularity of food trucks skyrocket over the past few years. It sparked an idea.

"If you can put gourmet food on wheels and take it anywhere, why not showers and toilets?" she asks in a launch video for her nonprofit organization, Lava Mae.

Sandoval's reason for starting Lava Mae was simple: She believes all humans have a right to be clean. Lava Mae's website notes that there are in San Francisco. About 3,100 of them live on the streets.

Lava Mae Bus

After Sandoval came up with her idea to help the homeless, she saw a story about the city replacing old Muni public transportation buses with a new fleet. She immediately sprang into action.

"I want those buses," she thought to herself. "So we reached out to Muni, and we found out that they have a donation program."

Perhaps then the most difficult part of the project began: fitting the buses for the plumbing necessary to run showers and toilets.

"We brainstormed for a couple months about how this could even be possible in a city like San Francisco, which is so ridden with permitting and regulatory hurdles," architect Brett Terpeluk said. "The biggest challenge, I think, was how to deal with all of the black water which is generated from two showers running every half-hour, 8 hours a day."

Terpeluk and his team devised a plan in which the buses connect to city fire hydrants for the water. Each bus is outfitted with a 50-gallon hot water tank that uses propane. Showers onboard are digitally controlled and supply both hot and cold water.

"Lava Mae is not about ending homelessness," Sandoval says. "What we are about is providing hygiene, because we believe that hygiene brings dignity, and dignity opens up opportunity."

CBS San Francisco reports that the cost to convert an old bus is $75,000. Lava Mae is kicking off a pilot service this month and hopes to have a full launch with four buses by next spring.