Cell phones falling into water are comically common and disturbing at the same time. It needs some quick action as well as damage control. In order to salvage the situation, there are a few things that you can do. Get it out of water quickly and dismantle all parts. The SIM card should be saved first as it contains all data. The device should be put into absorbing towels and dried off.
A good technique to achieve that is to ward off the phone into a sealed plastic bag with silica packs. You have to be very patient and not put in the battery to check the status of the phone as it can result in short-circuit.