Hi @alin93 ,
How did you clean it?
Did you use Isopropyl Alcohol 99%+ (available from electronics parts stores) with a soft brush to gently brush away all traces of corrosion and water?
Did you remove any metal shields that may be covering components and check under them, as the water may have got in under them and corrosion is occurring there?
Did you disconnect all flex cables and clean the cable ends and the connectors as well with IPA?
These are just some of the things that have to be done when water comes into contact with electronic devices, especially those that have the power connected to them all the time, such as mobile phones.
Unless the battery is disconnected from the systemboard, there is always power available at certain points on the board, even when the phone is off, as the Power button is not a power isolating button. Think of the phone as being in an extremely low power state when it is off and not that it is totally disconnected from the battery.
Water, electricity and electronics are not a good mix. The impurities in the water creates corrosion and provides paths for the electricity that were not in the design of the phone and can damage the components. The corrosion starts immediately and is ongoing until it has been all correctly cleaned away.
Here’s a link that may be of some help. Electronics Water Damage
You may have to open it up again and check that you didn’t miss anything when cleaning