Functions f/i//W/i/ and f/i−1//W/i−1// are optimal return functions per state variables W/i/ and W/i−1/ in time stages i and i−1 respectfully; Pel/i///Qd/i//= return function from stage i per decision variable Qd/i/; and Eq. /4/ expresses soil moisture constraint; Eq. /5/ expresses the constraint that the model will disregard cases when precipitation exceeds evapotranspiration; Eq. /6/ expresses the cost efficiency constraint /separately elaborated hereinafter/; Eq. /7/ expresses constraint of water abundance from borehole; and Eq. /8/ defines the initial value of soil moisture, present in Croatian climate conditions in winter and early spring