“Sacred water” was the theme underpinning the 37th annual Carnaval celebration in San Francisco, and it brought tantalizing ocean-themed floats to the Mission District on Sunday, along with frank messages about water conservation. To him, “sacred water” — or “Agua Sagrada,” in Spanish — has a special significance to Latino cultures. Many ancestors did a rain dance before the harvest, and a prayer ceremony to honor the rain, he said. Granted, many participants in this year’s parade interpreted the theme in more festive ways, by dressing in shimmery mermaid skirts or costumes that rippled with jewels. A “Rumbagua” (“Rumba de Agua”) float, designed by staff at the Mission Cultural Center for Latino Arts, used acquatic blues and island dance styles to represent Cuba, Puerto Rico and the Dominican Republic. Water wasn’t the only sacred element in this year’s parade, which featured music and dancing from a wide patchwork of cultures, including Brazilian samba, Trinidadian soca, Puerto Rican salsa and Colombian cumbia.