im sure this question has popped up many times, but what is a good substitute for water? (keep in mind im using styrofoam as a base)

cheers,
Smithy

First, make sure you cover the styrofoam with something, Celluclay, plaster of paris, etc.
I've used envirotex, a two part clear epoxy for depth and Woodland Scenics water effects for waves.
Here is a step by step I did and here is a much more involved one by Marion Ball.

Ahoy, mate, from one "smithy" to another!

Listen up, my friend, here is a very recent article published over at MSW that will give you a very convincing water effect, and quite reasonable, as well...and I'm sure that you could adapt the methods to your needs...

Making Water

~Gunny