Why is off button not working

@raunakjaju you have to treat it the same way as you would treat any other water damaged device.

Right now you should stop continuing to try to charge, sync or otherwise use your phone. This potentially can make a bad situation worse.This may further damage your phone.

The very first step I would take is to disassemble your phone. Use something like this video as well as this one to disassemble your phone. Now take a careful and close look at all components and connectors. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. You will have to remove all the EMI shields from the two boards.. If you do not remove the shields, you are not cleaning the board.

Once you got the gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for an Apple iPhone 3G but it is still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. Do not use compressed air for the cleaning since that can drive liquid as well as corrosion particles into areas that will cause trouble later on. You do not need to leave it to dry for a day. Isopropyl alcohol in the higher concentration will evaporate quickly and dissipate the water. The importance here is the cleaning. It would of course be best to get it ultrasonic cleaned Do not forget to replace the battery. This is a must and not an option. It will fail if you do not take care of it now.

After that, reassemble your phone and re-evaluate. For as long as you have not cleaned your board and replaced the battery, everything is just a guess. Keep in mind that water damage is the hardest to troubleshoot and to repair.

On your model, I would choose to replace the charging board and the flex since those are common items to fail. If you are stuck at anytime, or come across an oddity, you can post pictures of that with your Question Adding images to an existing question

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!