Occasionally I will "wash" dirty PCBs by spraying them with 50% ethanol, 50% water, then drying them with an air gun or the like to get the water off in a reaso

Occasionally I will "wash" dirty PCBs by spraying them with 50% ethanol, 50% water, then drying them with an air gun or the like to get the water off in a reasonable time. Nearly any properly designed board will not hold residual voltage for long when disconnected from power, so the slight conductivity of tap water is a non-issue.