I can't really as you say "adjust my mash and sparge water beforehand" without acid. My well water is fairly alkaline with with medium high bicarb at 7.1 pH. The other minerals that I usually concern myself with are present and pretty close to what I want for most styles. I adjust mash pH with lactic acid specifically for the grain bill I'm mashing. The only thing I add to my sparge water is lactic acid to lower the pH to my desired target depending on the beer style and kettle pH I want but always below 6.0.
I sometimes use gypsum and calcium chloride for styles like IPAs and some english/irish ales but for the most part I can get the water and mash pH I want by utilizing lactic acid or acidulated malt. I've tried a lot of different things. This works for me. Your mileage may vary.
Example: Today I brewed pilsner. I use pilsen water target in brunwater. It's soft water. Mine is closer to hard. The grain bill is 99% pilsen malt and a tiny bit of carpils because I'm too busy today to do a protein rest or decoct. srm 3.3. Only way to get my mash pH to 5.4 is acid. Today I used a little over a pound of acidulated malt with 19 lbs of pilsen and acouple ounces of carapils and hit 5.4. I adjust my lagers to 5.2 kettle pH so I can't sparge with 7.1 water. Hence the use of more acid. I've used distilled water in place of my water and cutting at different ratios and noticed no difference from using my water and acid. So that's my process and I'll keep it til I move. haha