If the sparge water pH is high, it can raise your mash pH potentially past 6 where you risk tannin extraction if the water is much above 170. You can use distilled or RO and it shouldn't cause the mash pH to raise past 6, but you'll need to account for that water being RO or distilled in your calculations. Some people do treat their sparge water with acid to lower the pH to the safe range but depending on the acid used it could affect the beer flavor (lactic acid is tangy for example).
"sparge" additions go in the boil kettle because they are pretty much just for flavor modification, it is too late for them to affect pH for mash enzymes. Additionally some water salts dissolve poorly in water, and less poorly but not perfectly in the mash as well. If your sparge water is treated with salts that do not dissolve well, you could try keeping it stirred up.