The iPhone is a pretty awesome smartphone. You can do all kinds of neat things with it as long as it has some battery left. There are all kinds of handy chargers available for these devices. If you would like to charge your phone with water, you should give these two products a look:
Hydrobee: powers your phone and USB devices from flowing water in rivers and faucets. It is a tiny hydropower turbine in a can with rechargeable batteries and a USB port.
myfc PowerTrekk: a revolutionary portable charger that generates electricity from water. Just add water an a myFC Puck with salt, and you are set.
You could always rely on solar and other emergency chargers to recharge your phone. The above chargers are useful when you are spending time on a boat or just don’t have access to other sources of energy.