Q. Can I use the (prison’s) hot water machine for Shabbos and add milk into the coffee?

A. If the hot water urn only dispenses hot water and nothing else, and when you take out hot water, no fresh cold water enters automatically to replace it, you can use it on Shabbos.

Fill in first the cup with the hot water and then add coffee, milk and sugar. Not the reverse, as you will be cooking on Shabbos.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a