The increase in global demand for food and biofuels, has led to an high demand for agricultural products. That situation impliesan intensification of production systems, and develop strategies to ensure stability against drought, and moreover a better levelsof productivity. Objectives that could be achieved with the irrigation of crops; however, it can promote negative impacts due tocumulative effects on soil quality, which depend on the chemical composition of the water used. This paper show the results ofa national study of freshwater quality, on 100 river watersheds (up to 100,000 ha), which correspond to a cumulative drainagearea of 70% of country surface. In these freshwaters the following parameters was evaluated: electrical conductivity, concentrationof major cations (Na, K, Ca, Mg), alkalinity, and pH. The results showed Ca, Mg, K, and Na concentrations in ranges of 0.0-45.1, 0.0-14.1, 0.019-16.8, and 0.78 -139 mg L-1, respectively. The alkalinity was in range of 32 to 420 CaCO3 mg L-1, and thisvariable was the most important contribution to get the different values of electrical conductivity of water, which had valuesbetween 71.6 and 1047 micro Siemens cm-1. These features allow propose at least 3 freshwater ecoregions (coastal andcentral-south; basalt; Northeast and southeast) at Uruguay, based on the chemical composition of studied freshwaters. Moreover,SAR values (([Na] / [(Ca + Mg) / 2] 1/2) of these waters shown a 99% of them has good quality characteristics for thedevelopment of irrigation, because they have a SAR below 10.