I’m not sure what to do about hot water.
I’m in Texas. The problem here is that the tap water is often too hot, rarely too cold. I was fortunate at the old house to never have the water coming out of the tap at such a temperature that it would reticulate film, but I have heard such tales. I must have been far enough from the water tower that the water cooled running underground to the house. I expect much the same in the new house.
My prior darkrooms had not had any heated water until this last one. When I built it 12 or so years ago, I installed one of those two gallon (yes, 2) little water heaters that plugs into 110V. It quickly proved to be useless. Maybe it was too small, or maybe it suffered from only being turned on intermittently, but it was disappointing. Eventually, an old microwave made its way to the darkroom and served very well for heating water to mix chemicals.
So, is hot water needed? Not always needed, but helpful when it is needed. (Such as for cleaning up.) It has been suggested in a comment to a prior post to use an immersion heater for making enough water for mixing chemistry. The microwave takes care of that. It is also been suggested to get a standard tank heater and that is a very practical approach. This time I would put in a 20 gallon, however, now that there’s room and I can get 220V to it. The other alternative is a point of use heater. This would not store and maintain hot water when I wasn’t using it.
The point of use option is the most expensive, but if I could find the right unit, it could be the most efficient and effective. I say “could” since I have heard both good and bad things about them, so I need to do more research.
But, I have made an interim decision: I am going to “plan for” a hot water side when laying out the plumbing, but I will not install a heater, yet. At a later date, I can put in a tank or tankless, or do nothing and be cold only.