Turn off the fountain and unplug it from its power source. Dump out any water and dry it with a towel.
Mix a solution of one-quarter cup bleach with one gallon of water in a bucket. Dip a scrub sponge into the solution and scrub the fountain thoroughly. Items that are constantly subjected to moisture are prone to mold. The solution will eliminate all mold and any other residue that is on the surface of the fountain. Allow the fountain to dry.
Sand the entire fountain with medium grit sandpaper. Go over every part of the fountain with the sandpaper to create texture. The rough surface will allow the primer to sink into the grooves and bond with the resin. Wipe away the sanding dust with a damp rag.
Move the fountain onto a drop cloth. Cover any areas that you don't wish to paint with newspaper and low-tack tape.
Spray the entire fountain with a thin coat of spray primer. Choose a bonding primer that is formulated for plastic. Make sure that the primer says "bonding" on the side of the can. Move the sprayer in a steady back and forth motion. Allow the first coat to dry to the touch and apply a second coat. Let the second coat dry for two hours.
Paint the fountain with spray paint. Choose a paint that is formulated for plastic. Krylon Fusion bonds well with plastics. Spray a thin, even coat over the entire surface. Allow the first coat to dry. Apply one or two additional coats.