If the phone is dropped in water, try this, if you have distilled water wash it in that, if not skip the Distilled water bit, then take some rice and seal the phone in a bag with rice. Rice absorbs water Let it dry at room Temp,

do not use use heating to dry it because what could happen is that, the metals will expand, then when it cools down they shrinks again and the phone will not work as well because they are out of their place.

Never turn it ON this will corrode the metals in the phone because of the electricity flowing through it. so let it dry first.