dropped j7 in water, wont turn on

Bambi Condie the very first thing you want to do is to no longer try to turn your phone on. The second thing you want to do is to clean your phone. If you do not clean it properly, you are running risk of having corrosion damage in the near future. Disassemble your phone completely and clean everything, especially the logic board, connectors and cable ends with 90%+ isopropyl alcohol. Use a soft brush to gently clean every "nook and cranny". Use something like this guide Repairing iPhone Liquid Damage for that. Even so it was written for an iPhone, the cleaning is still the same for your phone as well . While you clean it check your board for any missing or burned components. After that replace the battery. Re-assemble your phone and re-evaluate.