I can definitely confirm that the S4 Active is waterproof. I write for a winter sports blog and therefore wanted to test 2 key features of this phone, its waterproof capabilities and also how it works while wearing gloves.
I recorded 2 videos for these 2 features, so if you are interested you can see them at Snow Pursuits.
The phone was dropped in to a bowl of water and it worked fine after, although the mic was muffled until it fully dried. This is a slight issue as making calls is virtually impossible while the mic is wet. You can also use the phone in gloves, which is fantastic when you are skiing and want to do simple touch screen tasks such as read a text or change a song in your playlist.
Definitely a recommendation from me, especially if you will get the phone wet or want to use it without taking your gloves off.