Nuclear resonance absorption is induced in protons contained in mixtures of light and heavy water. The magnitude of the power absorption is used as a measure of the concentration of light water present and samples of known concentration are used to standardize the absorption.Two techniques for inducing the absorption are described, one appropriate for H₂O concentrations in the range 7-100% and the other for low concentrations. In both cases the signal output from the equipment rises almost linearly with H₂O concentration. Using the first method, a signal-to-noise voltage ratio of twenty is obtained with a 7% concentration. A similar ratio is obtained from samples with 0.2% H₂O by using the second technique. The effect of flowing low concentration samples through the apparatus has been studied. The signal output falls with flow rate and at 40 ml/s is half that obtained at zero flow. Suggestions are made for improving the stability of the equipment and for reaching a quantitative theoretical understanding of the absorption signal shapes observed.