Agreed. I do ph and use evaporated tap water. Here's what I have found. i experienced, and your experience may differ, is that during the early stage of life, first 4 weeks or so, my water is phd at aroun 7.3 to 7.5. What i discovered when the plant was young was that ph water of around 6.2 was hurting my plant. I think this is because there is a relation between acidity/ alkalinity and ph. The soil has a ph of a given value based on the TDS in its medium and when i fed with more acidic water the plant could not handle it. So i began watering with more alkaline water, again, 7.3 or so and corrected the issue. As the plant grew and required water to runoff i noticed that as the soils nutes became less, the runoff more accurately mirrored the input so i could now add nutes, ph to 6.2 and water my medium knowing what i put in would be what i got out. Soil has nutes ( tds ). Plants eat nutes ( tds ). Soil becomes neutral. Limited tds. Now you feed and balance tds and ph