The comparison of the radiation effect rates of the surface water polluted with radionuclides 137Cs and 90Sr and permissible levels (PL) of their activity is considered. A new approach to calculating the compliance index (CI), assessing the content of 137Cs or 90Sr in water, is proposed. The approach is based on the assumption of the CI dependence on the relative value of the deviation parameter. This parameter is determined in fractions of the minimum measured specific activity (MMSA) by the spectrometer. The influence of storage coefficient on the CI, which compensates for the inaccuracies in the MMSA calculation, is investigated. The algorithm for defining the stock coefficient as a function of the deviation parameter is proposed. The algorithm is based on the data from a series of measurements of a load. The equation for calculating the storage coefficient is presented. It uses a model to describe the distribution of the relative measurement error of the normalized Gaussian function. The suitability of the latter is justified by the results of measuring the activity of 137Cs. The representation of the Gaussian function argument by two parameters is applied. One is the deviation parameter, the other one adjusts the width of the distribution peak. The method of squared deviation minimization is used to define both parameters of the Gaussian function. According to the obtained values, the exponent optimally describes the experiment result. The universal equation for calculating the CI is established. A number of provisions of the theory of operational characteristics of the test are applied. The equation combines two separate relations, according to which the relation between CI and 137Cs or 90Sr can be calculated in the problem of the radioactive surface-water quality analysis. The calculations results of CI, storage coefficient and other parameters are presented. Measurement data of 137Cs activity in two model samples-analogues of the possible loads of surface water were used. The efficiency of the algorithm used for calculating the deviation intervals near the lower limit of measuring the activity of radionuclides is proved. The results correspond to the physical preconditions that are embedded in the spectrometric data processing model. The proposed ratios are efficient in determining the cleanliness class and water contamination rate in the process of interpreting the test results