I use our well water for soap also and always have except for my first few batches. I've never had any problems. We do have our water tested once a year.
I was told originally when I first started learning that undistilled water can cause DOS. In all the years that I've been soaping, I've had 1 batch get DOS, that batch was one of my first & I used distilled water with it. But it got DOS because I had it curing on white cardboard, so the moisture got trapped in the cardboard and was keeping the soaps moist.
This discussion was recently brought up in another group and honestly their reasoning didn't make sense to me. They said that it was to keep the impurities, iron and zinc out of their soaps. But a lot of these same people use goat milk in their soap. Goat milk is high in iron & zinc and if they're using local goat milk, wouldn't the goats be drinking the same kind of water?
p.s. Today I'm making soap using snow I collected yesterday from our first snow fall
