mesh colliders particle collions? physics stuff HELP! (photo inside)

hello everyone. is there anyway to code or use the standard assets to have a particle system like water not go through but stop or bounce off of a mesh? (a mesh with a mesh collider attached.)
here is a picture. it shows a model of a car and the particle waterfall system.

thanks doods[619-Screen+shot+2012-04-13+at+2.30.55+PM.png|619]

The old particle system (pre-3.5) can, using a WorldParticleCollider. The new one can only collide with a plane. Unless you program your own, tracing the pathes of each particle…

Searches in either Unity Answers or Google would have returned plenty of hits answering this very same question.