The quickest way to add water with reflections in your platformer game!
It's as easy as dropping an object into a room, as seen in the second GIF below.
Available for both GMS 1.x and 2.x.
If you're looking for top-down water, check this out.
The reflection and refraction shaders can be customized simply by changing some variables. The reflection opacity can be reduced to allow the water to be translucent.