I have a 2007 Focus C-Max with heated windscreen and heated washer jets. I use ordinary tap water to fill the washer bottle. I've noticed at timesthat the water squirted onto the windscreen leaves a residue that 'sets' a bit like clear glue on parts of the screen that the wiper bladesdon't clear. These marks take a bit of scrubbing with a car brush to get them off. Should I be using something other than ordinary tap water?