Hi @kangjun ,
As you know water and electronics and electricity are not a good mix.
''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.''
''First '''do not turn on your tablet''' and then you need to '''remove the battery as soon as possible''' from the tablet'' to minimize any further damage.
Then you need to dis-assemble the rest of the tablet and clean ''all the affected parts'' using '''Isopropyl Alcohol 90%+''' (available from electronics parts stores) to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, 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 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'' possibly work correctly again.
Here is a link to the ifixit guide(s) for repairing your tablet.
[[Topic:Kindle Paperwhite 3rd Generation]]
If this process seems too daunting, take your tablet to a reputable, professional mobile phone or electronics repair service experienced in liquid damage repair and ask for a quote for a repair. If you decide to do this, ''do it sooner than later''.