Hi @escapism ,
What is the model number of your tablet?
It may be able to be repaired. It depends on what damage has occurred and whether it is economical to do the repair
You need to open the tablet and disconnect the battery from the systemboard to minimize any further damage. Once the battery has been disconnected, DO NOT reconnect it and try to turn on the tablet again until it has been cleaned and repaired, as you will only be compounding the problem.
Also while rice may be good to eat it does nothing to fix the problems caused by corrosion
Don't Put Your Device in Rice. Here's Why
Water, electronics and electricity are not a good mixture. The impurities in the water cause corrosion whilst the water itself is a conductor of electricity and allows current to flow in areas not catered for in the circuit design of the tablet
You need to clean off all the corrosion and disperse any remaining water by using IPA 90%+ (Isopropyl Alcohol - available at most pharmacies). Do not use "rubbing alcohol" as it is usually only 70% or less, may contain scents and is not as effective.
The link below may be of some help in the cleaning process of the components affected by the water and corrosion.
Electronics Water Damage.
If the above process seems to daunting, I recommend that you contact a reputable, professional laptop or mobile phone repair service experienced in water damage repair and ask for a quote.