I dropped my Kindle Fire in water

The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the tablet’s operating design and could damage the components. The corrosion process starts immediately and continues until it has been cleaned properly

First do not turn on your tablet and then you need to remove the battery as soon as possible from the tablet to minimize further damage.''

Then you need to dis-assemble the rest of the tablet and clean all the affected parts using Isopropyl Alcohol 90%+ (available at most pharmacies),to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is only 70%, can contain scents and is not as effective. If you do check the label to verify the amount of IPA

Here is a link that in general, describes the process.

Electronics Water Damage

As always with electronics, especially surface mounted PCBs be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board.

Hopefully after you have done all this the tablet might continue to work correctly.

Here is a link to the ifixit Kindle Fire guide which may be of some help.

If this process seems too daunting, take your tablet to a reputable, professional mobile phone repair service experienced in water damage repair and ask for a quote for a repair.

If you decide to do this, do it sooner than later.