In this paper we consider the problem of building water canals with maximum capacity. By means of local maximum of two variable functions and gradient vector, we find optimal canal consisting of five similar bricks.\nThen we consider a canal consisting of 2n+1 7 bricks, and to optimize cross\ncut of it we use a geometric approach, from which we obtain the maximum\nvalue of a related multi-variable function, as more as, values of two geometrical series.