River

All the controls can be found in the Geometry Nodes panel.

Rain

This effect is divided in three main components:

1. Rain.Instancer - The particle system that emits the rain particles.
2. Rain.GeometryNodes - A geometry nodes setup which scatters water splashes on all the objects in the collection "Surfaces". The setup will automatically detect the faces of the surface that are hit by the rain basing on its direction, so there is no need to duplicate your objects.
3. Rain Pattern - A shader groupnode that applies a water flow effect to the input shader.

You can control some of the parameters of these objects at once (e.g. the direction of the wind). To do so, find the object Rain.Controller.
Rotate it to change the direction of the wind: splashes locations, rain drops rotation etc. will update automatically.
Some other render settings are inside the custom properties of the Rain.Controller (object properties > scroll to the bottom).