If you search NWVault using "Water Fall" as a keyword, you will find several "Tutorials" and "Visual Effects" (for NWN2) that were created by the modders community, including:
In the following section, we are going to try out Teper's Waterfall/Wet Cave and Fountain VFX Effects Pack.
1. First of all, download Tesper's Waterfall/Wet Cave/Fountain Visual Effects here.
2. Unzip the compressed file into a directory of your choice.