This particular method is usually used in backpacking for core temprature regulation by keeping the hot water bottle next to your body as you sleep. I have found that one bottle as a pilow and one wrapped up close to my core will keep me warm with just the clothes on my back for upto six hours in the late spring and early fall without a sleeping bag. Also when added to a sleeping bag near your feet and also at your core will keep you warm in the dead of winter. Other applications include hot showers and any other means you can think of for hot water.
***The usual warning for alternative boiling methods: "Alternative" in and of it's self should tell everyone that this is not a preferred method to boil water; therefore, if you have a metal container use it instead of plastic. Some research has stated that plastic will leach chemicals whenever it is heated. From my experience if the water changes color (see some of the pictures below) and smells of plastic then it is ovbiously not safe to drink. In an extreme emergency when no other means to boil or filter are avaliable then this method could be used, but long-term health risks must be weighed. As always filter then boil and if in doubt that the water is contaminated look for another source.***
So far I would always stone boil in plastic if I have to use plastic as it is quickest and seems to do 0 damage to the container. Stay with us as next week I will try another alternative method to boil water. As always feel free to ask any questions or make suggestion in the comments!