Approximate relative permittivity data for water down to −35°C have been derived from measurements of the Maxwell–Wagner interfacial polarization which occurs at the surface of emulsified water droplets. Although the emulsifying agent strongly influences this polarization in a complex way, a novel method of data analysis enables the permittivity and conductivity to be obtained in a simple and direct manner. The derived data are in essential agreement with literature data near 0°C. To within an estimated experimental uncertainty of ±2% the present data conform to a critical exponent expression with the same critical temperature (228 K) found for many other properties of supercooled water, though the divergence is very weak.