_jis_So, this was in September, the water was regular tap water as it comes in india, not distilled. He had a heating network at his home which he used to get the back panel off.
a friend of mine helped to immediately dry everything out
Describe exactly how he dried it, that's very important. The water wasn't distilled, I suppose. What kind of water was it?
Anyway, it's now clear that it's a hardware problem that was caused by the water.
_jis_Thanks man, I am checking those references you've been adding. I'll try them all and if no change, then try to get a spare.
He used a very brutal method, which in itself could cause damage. Water or moisture needs to be removed as gently as possible, see those references I've been adding. And the desiccation should take place as long as possible, ideally several days.
It is important that there is not a single hidden drop of water, or any moisture, left before the phone is subsequently turned on and used.
Otherwise, even over a long period of time, faults can gradually appear.