The Rain effect must be turned on -
To get the reflective ground when it rains -
Borrowed from a user on a Sonic Ether forum -
Line 333 ( might not be that exact line - use cont. F to search )in "gbuffers_terrain.fsh" looks like this: spec.g *= max(0.0f, clamp((wet * 1.0f + 0.2f), 0.0f, 1.0f) - (1.0f - w) * 1.0f);
Change "spec.g *= max" to read "spec.g += max"
Basically you just change * to +, that's it -
I don't know much about the water artifacts - post a screenshot for others so they can help you further