Water damage can take a lot of value out of your phone. The Gazellelab shows you how to check to see if your Galaxy S3 has water damage. The water damage indicators are behind the batter, and on the battery. Make sure to keep your phone away from water, steam, and rain.
Water Mark Indicator Location for each carrier:
T-Mobile= 1. behind battery — 2. on battery
AT&T= 1. Just to the left of the battery approx 2/3 the way up from the bottom of the phone there is a little hole with a normally white dot indicator. This will turn red if subjected to water — 2. on battery
Sprint= 1. behind battery (some have them , some don’t) — 2. on battery
Verizon= 1. behind battery — 2. on battery
Unlocked= 1. behind battery — 2. on battery — 3. behind headphone jack (must remove plate)