I've seen a few threads where people have gone a bit deep in mud or water and the alternator has fried etc but no conclusive answer as to how deep is safe?

I'm going to a 4x4 site this weekend with a water feature and it varies in depth depending on where you go in it. i need to drive the VX home again after and don't want to damage it!

So where should i go up to with the water with a standard air box and no snorkle etc?