This is how we convert ice into water during nag tibba trekking.

While trekking to nag tibba summit. We faced water problem. 

My friend @indiantraveller suggest putting ice into the bottle. There is temperature around - 10 degree Celsius. We start putting ice into the bottle and start trekking. After sometime temperature starts rising, and soon ice starts melting and we get some water in such area where no hope of water.

You can watch complete video here.