A joint event, with the theme Green Planet, Green Future, takes place from 9 a.m. to 2 p.m., Sunday, April 21. The Earth Festival features competitions for the best model solar race car and solar house. Kits are available at swetucson.org/solar. The Water Festival features theater and dance performances, workshops, music, live art "happenings," a mermaid and children's activities. Community groups and businesses host displays and exhibits for both events. Visit tucsonearthday.org or waterfestivaltucson.org for more information.