Will Relative density of water change based on the state it is in? Ie solid, liquid, gas.
What causes this change(if any) in Rd?
Yes the density of water changes with temperature in a non-linear way (which is important if you want life on your planet).
It has a maximum density at 4deg C and is unusual in that it expands (lower density) as a solid - see http://en.wikipedia.org/wiki/Water_(properties)#Density_of_water_and_ice
As a gas it's density varies with temperature and pressure like any other gas.