Hi,
Ensure that the battery remains disconnected from the systemboard until all parts have been very carefully and gently cleaned all over, with Isopropyl Alcohol 90%+ and a soft brush (you do not want to brush components off the board) and then allowed to completely dry.
Also check that the correct voltage is present at the battery terminals, by measuring the open circuit (or battery disconnected) voltage using a DMM (Digital Multi Meter-Voltmeter function).
When satisfied that you have done all you can, re-assemble the tablet and hopefully it may turn on successfully.
If it still doesn't start properly, at least you know that you can begin fault finding without having to worry about the possibility of errant circuit paths between components created by the water, (or more correctly elements, intended or not -think chlorine, fluoride, natural minerals etc, that are always present in all water, except distilled).