I lived in San Antonio for a while; really hard water. Water softeners were de rigueur there and added so much extra salt to the water that the softened water left a white, hard crust on negatives. So did the unsoftened water, but it was calcium carbonate instead of salt. Prints were affected too, unless they were carefully squeegeed before drying.
The solution (pun intended) was to use distilled water together with Photo Flo for the final rinse for film. The trick is to use a fresh solution and a rather generous volume let your negatives soak a bit in this solution - 3-5 minutes - not the 30 seconds or so needed for just the surfactant effects of the wetting agent. This gives the dissolved salts/calcium carbonate/etc. time to leach out of the emulsion enough not to leave any residue on dried negatives. Prints usually did alright with a good squeegee, but sometimes I would give them a final bath in "drinking water," which was widely available from vending machines there for 25-50 cents per gallon. Don't save and re-use the distilled water/wetting-agent solution. Try to use it "one session." Re-use can result in either salts or carbonate building up in the mix and negating the effect.
Most commercial pre-packaged developers (e.g., one-package developers from Kodak or Ilford) contain sequestering agents to deal with hard water components when mixed, so you don't need to worry about using tap water with them unless problems crop up. However, if you're mixing things from scratch or using kits from suppliers like Photographers' Formulary, etc., then it's almost a must to mix your developer with distilled water. I'd likely use distilled water to mix Xtol stock as well. Some stock solutions won't mix at all unless you use distilled water (think Stock Sol. B for PMK). When making a working solution from stock solutions, tap water should be fine. Note, however, that extremely hard water can affect your development time a bit. I had a 10% difference in time between using hard tap water and distilled.
Acidic stop baths can be mixed with tap water; they'll neutralize any carbonates by nature. Same with acid or neutral fixers. Alkaline fixers should be alright as well, since they are usually well-buffered, but I'd keep an eye on things. Washing in hard water is actually a bit more efficient than in soft water, but you definitely need the final rinse in distilled/wetting agent for negatives and it won't hurt prints to get a few minutes in softer water before squeegeeing and drying, especially if your water is really hard. I'd test a few and see if that were needed or not.
Best,
Doremus
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