An attempt is made to incorporate the physical mechanism in a distribution function of low flow in terms of baseflow recession. The derived distribution function contains four parameters of which two are determined from a traditional recession analysis of low flow periods. The other two are derived from a statistical analysis of the maximum length of “dry weather” periods when precipitation is less than an assumed threshold value. The distribution function with the same parameters can be applied to calculate mean low flow for different durations. It is applied and tested for summer low flow in southern and western Norway.