Hes talking about mapping and adding rain to a map. The problem is the rain does straight through Statics, I don't relieve there is a cure for this unless you gave each individual rain drop physics like a grenade. But this would cause phenoinal amount of LAG.
I think I saw a mentioning of a thread on effects, that don´t enter statics on the editor forum today. Umh.. Yesterday. Do a search there. There is also an option collisionenable in the effect stuff, I´m not sure if it applies to this, but give it a shot. It might also just be enabling other type of collision. I´ve used it for some soldier collision stuff with the effects.