Should fans bring their galoshes to see Julia Roberts in Three Days of Rain? The script calls for actual water onstage, and as one preview viewer put it online, “I could totally see the front-row people getting wet.” Apparently, rain-related issues were anticipated from the beginning; the producers hired specialists to make sure the indoor weather runs right. The stage rain requires four large underground water tanks installed by stage-effects specialists Jauchem & Meeh, as well as nozzled bars above the stage that can vary the size of the raindrops released. The director, Joe Mantello, is quite specific about the waterworks: “He dictates whether it’s going to be a mist or a torrential downpour,” says a source familiar with the show. The water is treated with UV rays to kill bacteria and heated to 110 degrees. The clean, warm water then drains through grates on the floor, and the actors change clothes offstage to prevent getting chilled. But the source assures us that all kinks will be fixed by April 19, opening night: “The actors will drip, but the audience will stay dry.” Next: Dems Pucker Up to Spitzer