The principle of the method specified is aspirating the sample into a gas flame of sufficient thermal energy to cause any sodium and potassium present to emit its characteristic radiation and measuring the intensity at a wavelength of 589,0 nm for sodium and 766,5 nm for potassium. Applies to water samples with a mass concentration of sodium and potassium of up to 10 mg/l. For higher concentrations, a smaller test portion is taken for analysis. The lower limits of determination are less than 0,1 mg/l for both sodium and potassium.