I originally bought one for a a trip to Hawaii and I was able to take fantastic underwater photos and video with my iPhone and upload them immediately. Here's a video I edited that was taken using the case (at the end where you hear sound I'm not using it). The only real downside is that sound is largely gone because of how the case works (why vacuum). They have waterproof earbuds/mic for $40 though.
It's a fantastic case because it's the only one where depth is only a matter of crush depth, which you won't be going to. It has no real max fail depth. It will NEVER leak and you'll know that because you evacuate the air before you ever get it in the water. If it's leaking it'll blow back up before you dunk it.
There's a story where a guy lost his in a lake for one month. When it was found the phone charged back up and turned on, no issues.
It's cheap ($30-$40 IIRC) and has a lanyard and neoprene floating armband you can use, or not and fits multiple smartphones as it's not designed for any one design.
I've used it in the water many times since that trip and it's yet to fail.
Anyway, now I'm between the disposable camera and this Panny getting good reviews. Has both pics and video but I just can' justify the cost on a camera I'll use maybe once a year... if that. And I still need to buy the sd card too, LOL.
Thanks again for all the great suggestions!
Edit: Can a mod please move this to the proper forum. I think it should be in accessories. Thanks.
Another option is you could just get an Xperia and then swap your sim from the iPhone into the Xperia whenever you are near or in water, or if it might rain. Then when you're back in dry conditions you can just put the chip back in your iPhone.