why we buy water resistant phones

i bought an iphone 7 around march this year on contract yet the features of the phone are great only to found out that one feature of the phone didn't work on the even of my phone fall in to bath tub water and the phone went blank afterwards booked it for repair at cell c and i was told to pay R8500 to replace my dead phone my question is why the features say Rated IP67 (maximum depth of 1 meter up to 30 minutes) under IEC standard 60529 but my phone didn't survive bath tub water phone still on warranty