I noticed several times while washing my hands that accumulated water when starts streaming vertically does not flow vertically in straight line on vertical porcelain surface under the force of gravity. It rather flows in strange zig-zag like path and the flow changes its direction rapidly and erratically from left to right and vice versa. Intuitively, it seems that the straight vertical path for the stream is the most physically economic path.
Is this well studied phenomena? What is the physical explanation? Is there a mathematical model that can predict any aspect of this type of flowing stream?