It looks like Mathematica (I'm using 14.0) accepts "Density".
ThermodynamicData["Water", "Entropy", {"Temperature" ->
Quantity[450, "Kelvin"], "Density" -> Quantity[1.431, "kg/m^3" ]}]
With answer
Quantity[7223., ("Joules")/("Kelvins" "Kilograms")]
Will that work for your need? If not, I'd like to understand why.
