How do I diagnose water damage severity?

Hi @daven9433

The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the phone's operating design and could damage the components. The corrosion starts immediately and is ongoing until it is completely cleaned away.

Drying the phone doesn't really prevent the affects caused by corrosion.

Corrosion damage is usually obvious but component damage may not be and unfortunately there doesn't seem to be a schematic diagram available online for the phone at least none that I can find. Even the official Google Pixel repair manual only shows how to dis-assemble and re-assemble the phone.

First do not try to charge or to turn on your phone and then remove the battery as soon as possible from the phone to minimize any further damage.

Then you need to dis-assemble the rest of the phone and clean all the affected parts using Isopropyl Alcohol 99%+ (available at electronics parts stores) to remove all traces of corrosion and water. If possible do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives which may leave conductive residues and is not as effective. If you do have to use it check the label to verify the amount of IPA. The higher the percentage of IPA the better

Here is a link that describes what happens. Electronics Water Damage

As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board. Remove the shields that may be covering some components as the water may have got in under there. The ends of any flex cables and their connectors need to be cleaned as well.

Once you get it totally clean (or as clean as you can) and reassembled, try wireless charging the phone first and check if that works, just in case the problem is only on the charge board. If it doesn't charge at all, you may have to also replace the battery as well as it may have totally discharged beyond recovery.

Hopefully after you have done all this the phone might possibly work correctly again.

Here is the ifixit Google Pixel 9 repair guide that may help.