A design principle for a meter for low water content in petroleum products is proposed in the paper on the basis of characteristics of polarized electromagnetic waves. The results of the theoretical study of the interaction between electromagnetic waves and artificial anisotropic substance are given. Characteristics of waves propagating parallel and perpendicular to the electric lines of force are indicated. A polarized-wave speed differential during the interaction with the artificial anisotropic substance is determined. A definition algorithm for low water content in petroleum products is given with account of the polarized-wave speed differential and the dielectric permittivity of the petroleum product.