Sorry about ur phone mate but as far as I know, Water Damage isn't covered by Sony's Standard Warranty, because what if your flaps were open? I am sure your flaps weren't open, but that is what they would tell you. Because they can!
If Sony covered water damage, every person with a water damaged phone due to carelessness of not closing the flaps will cry foul and request for their phones to be fixed for free. And how many phones do you think Sony would fix for free every day? All over the world. And not just the Z2, other devices too. So... Thousands?
Bottomline, unless Sony makes a phone with all WaterProof ports, totally waterproof (No need for flaps). Then they will always have the option to chalk it down to your mistake. Sad! But True!