From the fine article: "Over the past 3 years, W7-X’s creators stripped it down and replaced all the interior walls and fittings with water-cooled versions, ...

From the fine article: "Over the past 3 years, W7-X’s creators stripped it down and replaced all the interior walls and fittings with water-cooled versions, ..." I am guessing that the water used to cool the interior walls will get hot in the process...