Risks associated with water in a powered-off circuit
When a completely powered off circuit is exposed to tap water and dried, there is no obvious hazard as there is no electricity flowing. Though I don’t recommend applying water to electronics and then drying it. However, when electronics circuits are exposed to tap water and then dried eventually, the metals in circuit can eventually corrode and thus damage the circuitry. This can either result in a short circuit or break in connection and result in failure. The issue lies with tap water containing impurities like ions, metals, and gases. This water combined with metal will result in some form of corrosion.