Water in reactor is defined using a space warp. Space warps don't render, so if you want the water to appear in your final animation, you need to provide reactor with a geometrical representation of the water. To do this, you need to bind a plane or any other planar geometry to the water. The plane will deform according to the Water space warp, and you can then render it as part of your scene.
Binding an object to the water applies a modifier to that object, which lets you set a scale strength for the deformation. For example, if you set this scale value to 2.0, any water deformation is doubled for the vertices in the object.
To bind a plane to reactor Water:
Draw a plane the same size as your water in the viewport. Put it in a different place so you can easily link the two.
Click the Bind To Space Warp button on the main toolbar.
In the viewport, drag from the plane to the water space warp, or vice-versa.
The reactor Water (WSM) modifier appears in the plane's modifier stack.
Move the plane to the same position and orientation as the space warp (or vice-versa).
Water WS Modifier Properties rollout
Scale Strength—Acts as a multiplier for the geometry's deformation by the water. Increases or decreases the deformation applied by the Water space warp.
Reset Default Values—Returns Scale Strength to its default value: 1.0.