iPhone 3GS won't power on and stay on without charger

Hi Joshua, to take care of your water damage correctly you need to disassemble the phone to fix it right, here is a guide to step you through it, iPhone 3GS Teardown after its in pieces inspect everything for corrosion or rust and remove it with alcohol and a toothbrush, make sure it's completely dry before you reassemble it, sometimes the battery will be shorted out and need to be replaced, if it wont power up after this procedure get back on here and post a question and we can help, if you do this please let me know if it works, good luck ! If this answer was helpful please remember to mark it accepted.