and we were genuinely quite stunned by how hot it kept our water over 24 hours. Most of the ice in our cold drink was still solid after 24 hours, too – you could fill your Thermos in the morning ...

"Like coffee in a thermos, this water will also stay hot," Granstrom says. The excess heat from summer can now be used to heat the water in the caverns and in winter, it can be tapped into to keep ...

put one tablespoon of powdered soap for automatic dishwasher into thermos. Fill with hot water and let it stay overnight with cap off.