I remember you could make them but I guess not. I wouldn't mind also adding them in Daily points shop or something. Support nevertheless.
That might've been the case at some point, currently I believe I've tried all possible ways, cannot add water to the cups be it through sources like wells or sinks, or through items like bucket of water or the humidify spell, the 2nd way of making them doesn't work either because although you can add water to bowls, you cannot heat them on ranges.
I personally think this potion could be simplified a bit ( removal of heating element as example ) so there's no need to code in stuff that's not used for anything else in the whole game. Just like there's no need for roots in case of antidotes. If it's too much of a hassle simply adding it to a daily shop would be a nice alternative.