In the scene where the crewmembers go into the reactor compartment, there is a mysterious blue illumination to the water. At first I thought it was just a Hollywood vision of what radioactive water might look like.
But in watching one of the making-of featurettes, the director mentioned the "Cherenkov effect" which is a byproduct of radiation emitted when a charged particle passes through an insulator at a greater velocity than the speed of light. It emits a characteristic "blue glow" common to nuclear reactors.
To create the blue water they added tonic to the water on the set and lit it with ultraviolet illumination to create a replica of the Cherenkov effect.