Why deionized water, and nothing else
Tap water in Hillsborough County is hard. When it dries on glass it leaves behind the exact mineral spotting you were trying to remove. We run every drop through a reverse-osmosis and deionization stack until the total dissolved solids read effectively zero. Pure water is aggressively thirsty — it pulls dirt into suspension on contact and then evaporates leaving nothing behind. No soap, no surfactant, no residue for the next dust storm to stick to.
