What happens to retired public transportation buses? In San Francisco, many are being turned into toilets and showers on wheels! Doniece Sandoval, the Founder and CEO of Lava Mae, uses structural engineering to build these mobile hygiene units. Sandoval began the project after discovering that there was only 16 shower stalls accessible to the 3,500 homeless men, women and children in San Francisco. Her mobile shower design became a reality with the help of structural engineers, who figured out how to store, heat, and dispose of water for showers.