Santa Rosa Water is opening its doors to the Laguna Treatment Plant for “Trick-or-Treatment: Mysteries of the Laguna Treatment Plant,” a free and spooky open house where the community can get a behind-the-scenes look at how wastewater is treated and learn more about the people, science, and equipment that help keep our community healthy and our waterways clean and protected. Family-friendly costumes are encouraged. There will be something for visitors of all ages, including spooky science, hands-on activities, equipment demonstrations, food, candy, giveaways, and more.  Admission to the open house is free, and no RSVP is required to attend. Saturday, October 17, from 10 a.m.–2 p.m. Laguna Treatment Plant, 4300 Llano Rd., Santa Rosa. To register for specific tours, visit srcity.org/2898/Tour-the-Plant.