An analysis of the seepage through unconfined aquifers with lower boundaries of any shape is presented. The differential equation describing the flow includes a term that involves the pressure distribution on the lower boundary. Although in many problems all the required pressure distributions that enable the seepage problem to be solved are not known exactly, an inspection of a given problem gives extreme values of any unknown terms with a final result of known precision. The application of the analysis, checked by electric analog experiments, is illustrated by two examples of seepage problems: first, the seepage over an inclined plane between two parallel ditches; and second, the seaward flow of fresh‐water fed by a freshwater reservoir or by rainfall and supported on saline water from the sea.