As someone who's done metalwork; with a standard oil-barrel size quench bucket, you do not switch out the water every time you quench something unless you are utterly OCD; water lost from contact steam takes a whole lot to start losing any significant amount. Likewise, the amount of water used for (of all things) gem whetstonery for a single gem could fit in a drinking glass.
If you want to make it REALLY labor-intensive;
Yes I know quenching will not evaporate a whole bucket of water but their are myriad uses for water that easily add up too a bucket per item forged. Water would be used to quench the coals of the fire when work is done, to clean and polish equipment, evaporation in the hot environment will result in more loss of water from the quenching bucket then actual quenching.
As for making it "REALLY labor-intensive" you betcha, metal working in the middle ages was a VERY labor intensive activity which is why metal was rare and valuable. Having to fetch another ingredient in addition to metal and fuel is only scratching the surface, I think eventually having some air-bellows which need power supplied to them before any forging or smelting operation can be conducted would be a good start.
As for gems, I've always assumed that a raw gem bearing stone contained a large number of various sized gems and all of these get cut into a collection of stones, how else can you 'encrust' an item if not with a collection of gems. Thus if each gem is using even a mouthful of water the grinding of all them will require a bucket of water. Again a single bucket fetch task is almost trivially quick and gem cutting is currently WAY too fast, I have never needed to use more then one gem cutter to process all the gems I could find and even then the cutter will go through years of accumulated gems in a matter of days.