I had a person email me and ask me about static electricity building up on plastic slides and interfering with her child's cochlear implants. We contacted one of the manufacturers that KaBOOM! works with (Playworld Systems) to find out what's up. J. Curtis Cleveland, the Director of Engineering at Playworld Systems confirmed that this was a problem with any "rotomolded polyethylene slide". Manufacturers have been working on a way to address this for years now, but haven't found a good solution yet. All of the additives just bleach out of the plastic after a couple of months.
So what's a person to do? You can spray the slide with an anti-static spray or a solution of liquid dishwashing detergent. This should noticeably reduce the static until the rain washes it off.
Carrie