Are you wondering how the Galaxy S4 Active or even the Xperia Z are both waterproof.  It is quite very simple to understand. how is galaxy s4 active waterproof I often wonder if these waterproofed phones overheat more often than their regular counterparts since everything is sealed. The Galaxy S4 Active becomes waterproof only when you properly seal it according to instructions.  The back case needs to be snapped at all points firmly.  The Galaxy S4 has been manufactured to withstand water and you have to do your part by snapping the back case on properly to seal it. The Xperia Z on the other hand doesn’t have a removable back cover.  Sony sealed it so it becomes waterproof and unlike the S4 Active, Sony has decided to not allow users to remove the back battery case. Here is a video on disassembling Galaxy S4 Active, so you can get an idea of how it is waterproof.