Summary. The objective of this paper was to analyse the sodium levels in the spring water, surface and groundwater in Dalmatia during 2003. The sodium concentrations were computed from the difference between coefficient K (the ratio 1 between the chlorides and sulfates sum and the carbonate hardness) andK (the ratio between non-carbonate and carbonate 2hardness) and carbonate hardness. The average sodium concentrations have been expressed by a median and they ranged from 1.8 mg/L Na to 17.6 mg/L Na in the spring water, in the surface water they ranged from 1.0 to 502 mg/L Na and in the groundwater they ranged from 11.1 mg/L Na to 124.3 mg/L Na. In the spring water the sodium concentrations varied from 32% to 217%, in the surface water from 40% to 159% and in the groundwater from 77.3% to 180%. According to the corro-siveness coefficient K , 83% of the spring waters are classified as non-corrosive and 17% as water with a low degree of cor- 1 rosiveness; 84% of the surface waters are classified as non-corrosive water and 16% as very corrosive; all groundwater is classified as very corrosive water. Out of the total of 60 analyzed water resources 64% are classified as hypotensive, 20% as normotensive and 17% as hypertensive water.The drinking water has been defined as hypotensive (<10 mg/L Na), normotensive (from 11 to 20 mg/L Na) and hypertensive (>20 mg/L Na) by relating the sodium concentration projectively with the notion of arterial pressure knowing that an increased sodium concentration in blood increases the blood pressure.From the informatics standpoint the data related to health should be classified into data bases which can serve as a methodological starting point for studying the influence of sodium upon human health. Consequently, epidemiological studies should relate various sodium levels in drinking water to other factors which affect human health.