Experimental values of the dielectric constant of water suggest that, for temperatures greater than 400 K, the integral in the Kirkwood dielectric‐constant equation, which involves the intermolecular potential function, is a simpler function of temperature and pressure than of temperature and density. An equation has been fitted to values of this integral calculated from experimental values of the dielectric constant for temperatures from 238.15 K to 823.15 K and to pressures of approximately 500 MPa for temperatures greater than 273 K. The equation of ε thus has explicit variables T, ρ, p and gives a good representation of the available experimental results. The quality of representation of the experimental results has been compared to that of previous correlations of the dielectric constant. The new equation is applicable through wider regions of independent variables than the previous equations and is capable of sufficient accuracy to provide values of Debye–Hückel limiting law slopes which are as accurate as the experimental results allow. Values of Debye‐Hückel limiting‐law slopes are tabulated.