A method of reducing computation of water tolerance by projecting touch data is disclosed, targeting the handheld devices. The method targets first at obtaining a difference array, followed by extracting minimum values of rows and columns of the difference array to obtain a row projection list and a column projection list respectively. By repeated implementing of mutual capacitance detection, ghost water blocks can be wiped out from the multiple water blocks. Once integrating with a local spatial boundary detection algorithm, the sensed signals of intended input located within a rectangular water block yet beyond a real water block are consequently detected. The computational algorithm of the water tolerance of this invention is successfully built into the touch panel controller due to its substantially reduced computation.