Cold water goes into one end, and thanks to the large surface area of the device it can be heated quickly to boiling point before it comes out of the other end. While it's being used, a normal pan can be placed on top of it to cook as normal, meaning that you don't have to use as much fuel. The device can also be used to heat water with the sun. Filling it full of water and leaving it out in direct sunlight should raise the internal temperature to about 80°C over the course of about 20 minutes. The hot, uncontaminated water that comes out can then be used to drink or to clean safely. An off-the-shelf digital thermometer can be placed into the output tube from the coil to monitor required temperatures for pasteurization.