So it’s been a while but in case this info is useful to anyone, I’ve found a nice solution that works for me. My grocery store’s “purified drinking water†tests at pH right around 6.0, and the “natural spring water†tests in the upper 7s. After lots of trial and error, I determined that adding half a cup of spring water to a gallon of drinking water made the resulting water be right around 6.5, which is perfect for my FFOF/Nature’s Living Soil grow. Hope this might be useful to someone else!