Most of the machines listed above require you to put coffee in the filter so you can brew. If you don’t add any coffee, all that comes out is hot water, and as such, it is possible to use the machine to boil water. Also, some manufacturers recommend that you boil water without including grounds when you haven’t used the coffee machine in a long time. This way, when the hot water passes through the system, it cleans out all the dirt that may have accumulated.