Low flows are a good measure of the waste water recipient self-purification capability. The regional statistical analysis is an objective way of assessment of the required low flows. This paper presents the principles and key phases of the regional statistical analysis. The advantages of this method are a reduction of the outliers influence and the assessment of low flows on ungauged streams and stream profiles. The method is illustrated with the results obtained by the required low flows regional statistical analysis in Serbia (Yugoslavia) with 59 hydrological gauge stations in the scope, which data has the same length of 39 years, from the year 1956 to 1994.

Drought characteristics (minimum flows, drought duration and volume deficit) of the Moraca river near Podgorica, Montenegro (Yugoslavia) are analyzed using the peaks over threshold method based on renewal processes. It is also shown that volume deficit and drought duration are highly correlated.

Withdrawal of water from surface water network should be concerned with preservation of the environment, meaning that the low flow regime in streams should be preserved within the range of natural regime. In order to formulate criteria for minimal allowed flows in streams, it was necessary to perform statistical analysis of low flows in rivers in Serbia (Yugoslavia). The criteria for water withdrawal are proposed on the basis of characteristic ratios between minimum and mean flows. Different criteria are proposed for cold and warm seasons.

After the year 2000 the issue of a water qualitative and quantitative monitoring increased in importance as a consequence of the provisions of the Framework Directive 2000/60/EC. In this context agriculture is required to use more efficiently the unconventional sources of water. In the enclosures located at the scientific bases from the Danube meadow during the vegetation period from April to September the natural risk factors alternate, being represented by the hydric excess, mainly generated by phreatic excess, and the deficit of humidity from June to August (14, 15). In these conditions the engineering works performed are complex, being required a sizing for mixt task 0 controlled discharge and supply (2, 3, 10, 13). For finding the volume of water resource which transits the drainage works and the capacity of transport it is required to be known first the flow of the absorbent drain.