This is an interesting Kickstarter project that looks like it will be funded by September 11th and shipped by January.
The Estream is a small generator that converts moving water to charge an internal 6,400mAh battery and be able to power and charge usb connected devices.
It produces 2.5 to 5 watts of energy and can fully charge the 6,400mAh battery in 4.5 hours. After that it can power your devices twice as fast as a regular outlet.
Do you think this would be useful to you? The first supporters can get it for $180.
Source: https://www.kickstarter.com/projects/hyerinster/estream-a-portable-water-power-generator-fits-into