Watertight is a hard engineering problem to solve. If it isn't a vacuum or loaded with some other gas then you will get water coming in because of temperature c

Watertight is a hard engineering problem to solve. If it isn't a vacuum or loaded with some other gas then you will get water coming in because of temperature cycles causing the device to act like a pump, which in a phone are a problem because you will have temperature fluctuations caused by charging, usage and environment.