Microwave method for measurement of water content in a dielectric liquid is considered. The method provides independency of measurement results on the value of dielectric permittivity of a water-free liquid. A monitored dielectric liquid is sounded within a measuring section by electromagnetic waves in two measurements at fixed frequencies f1 and f2. Different values of water dielectric permittivity relate to these frequencies. As results of these soundings appropriate values ε1 and ε2 of dielectric permittivity of a water-containing liquid are determined. Under phase measurements values ε1 and ε2 are determined by measured phase shifts Δφ1 and Δφ2 of electromagnetic waves of corresponding frequencies f1 and f2 after propagation of these waves through the layer of a monitored liquid. A metal waveguide containing a monitored liquid is used as a sensitive element under amplitude measurements at two fixed frequencies that are lower than a cut-off frequency of its lower mode of this waveguide. Amplitudes E1 and E2 of electric field strength are measured at corresponding frequencies f1 and f2 under excitation of electromagnetic waves in this waveguide at one of its ends and reception of signals at its second end. Values ε1 and ε2 are determined by measured amplitudes E1 and E2. Water content is founded as a result of joint functional processing of ε1 and ε2. At least one of the frequencies f1 and f2 is chosen in microwave frequency range where frequency dispersion of dielectric permittivity of water takes place at this frequency.