In order to evaluate experimentally the susceptibility of a Vertisol to irrigation with poor quality water, the effect of a Na and Ca salt mixture and its concentration on the hydraulic conductivity of this soil was studied. The parameters studied were the sodicity level expressed as the sodium absorption ratio (SAR) and the total electrolytic concentration. SAR values of infinity , 100, 50, 10, 5 and 0 were considered and in each SAR value electrolytic concentrations of 1000, 500, 250 100, 50 and 0 (distilled water) meq/litre were studied. The turbidity of the leached effluents was determined and considered as an indicator of the dispersion of organic and inorganic colloids. For a SAR equal to infinity the hydraulic conductivity started to decrease as an electrolytic solution of 500 meq litre was applied and it reached zero when a solution with concentration of 10 meq litre was applied. For SAR values of 100 and 50 the hydraulic conductivity remained constant when the concentration of the electrolytic solution was less than of equal to 100 meq litre, above which the hydraulic conductivity began to decrease gradually. When electrolytic solutions with concentrations less than 50 meq litre were applied, the hydraulic conductivity decreased until it reached zero. These reductions were attributed to: (a) an initial swelling of the colloidal fraction when solutions with concentrations greater than 50 meq litre applied and, (b) a colloidal fraction dispersion as a result of a dilution (i.e. <50 meq litre). For a SAR equal to 0 the hydraulic conductivity did not decrease when distilled water was applied, whereas for SAR values of 10 and 5 it decreased up to 60 and 40% respectively. Furthermore, it was also found that for high SAR values the colloidal dispersion was considerably increased; however, for low SAR values this phenomenon was not observed. These soil sodicity conditions affect the soil moisture content because as the exchangeable sodium percentage increased, the soil moisture content increased too.