Pure water (no minerals,salts etc) is an insulator.add almost any contaminant and it bcomes a conductor.So,even if its only soft water wash away.Soft or better distilled water leave littlt or no conductive crud behind.The 2 hours at 40C(120F) sound about right for most computer and accessory boards.I like to steal the wife's makeup brush rather than use cotton swab(cotton can be a conductor) P.S.Any potable water is usable but use distilled water for a rinse.Bath time now?