One less known but very very cool feature of LuxRender is the ability to use measured data from real materials. In the example below the color of the water was not selected from a color swatch. Instead a text file with data measured from actual water was used. You simply tell LuxRender to use that instead and Lux takes care of the rest.
Download .blend file here.
Blender 2.65 and Luxrender 1.2RC1