Try distilled water...it's free of dissolved minerals thus won't leave spots, especially on a hot or warm engine. Works like a charm. You can get it at any food mart or grocery store for about .80 cents.
“Courage is fear holding on a minute longer.” -General George Patton Jr.
2008 FLSTC with SE Stage II 103ci Big Bore, 255 cams and V&H Big Shot Longs
Stock: 79.43 ft-lbs of torque / 66.41 hp
SE Stage I: 85.57 ft-lbs of torque / 72.44 hp
SE Stage II: 108.22 ft-lbs torque / 88.13 hp