Sony xperia not waterproof

Sony and Vodacom both claims that the sony Xperia Z3 is waterproof, if it is so waterproof how come my phone got water damage? Now i have to wait 6-8 weeks for vodacom Sony to see if they can fix the damage or replace the phone. If the phone was waterproof as they claim, then it should not have gotten water damage. They should state that the phone is only water proof for about 4 months, after that period it is not anymore.