Research carried out in the hydrological years 1997–2002 investigated the concentration of nitrates in drainage waters from three sites differing in physiographic, climatic and soil conditions. The compounds were determined one or two times per month in the period with outflows. Chemical analyses were performed using spectrophotometric method with 2,6-dimethylphenol. It was found that the drainage waters contained high amounts of nitrates: the mean ranged from 67.7 to 105.0 mg NO₃ · dm^–3, and the maximum values exceeded 240 mg NO₃ · dm^–3 and usually appeared in early spring. The mean concentration of nitrates constituted 36 to 45% of the maximum value, so the range of ratios between the mean and the maximum was narrow. If such a result is confirmed in further studies involving a larger number of measuring series, it would be possible to suggest using the mean value for the description of an experimental series. This is a measure that well describes a sample and is independent of incidental single values diverging from the others in the series.

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