Early on, softened water made by technologies like zeolite softening or chilly lime softening was a precursor to modern-day UPW treatment. From there, the expression "deionized" water was the following improvement as synthetic IX resins were being invented in 1935 then became commercialized in the forties. Amongst those two extremes https://newsprospect.com/the-ultimate-guide-to-pure-water-cleaning-with-a-water-fed-pole-for-solar-panel-cleaning/