The formation water (brine) isothermal compressibility data is published in 1990 by McCain.
Math and Physics
At pressures above bubble point:
The correlation is valid only for temperatures between 200 and 270F, pressures of 1000 to 20000 psia, and salinities up to 200000 mg/l.
We, at pengtools.com, are calculating water compressibility below the bubble point with the same equation at the moment.
Example. Calculating water isothermal compressibility
Example source 
Calculate water isothermal compressibility at 3500 psia and 165°F?
The solution is also available in the PVT software model at [The solution is available in the PVT calculator software model at www.pengtools.com
- = pressure correction, res bbl/STB
- = water salinity or solids concentration, mg/l
- = pressure, psia
- = Temperature, °F
- Water bubble point pressure
- Water compressibility
- Water density
- Water formation volume factor
- Water salinity from density equation
- Water solids concentration
- Water viscosity
- Gas/Water Interfacial Tension