Early on, softened water produced by systems like zeolite softening or chilly lime softening was a precursor to present day UPW remedy. From there, the term "deionized" water was another development as synthetic IX resins were being invented in 1935 and afterwards grew to become commercialized in the nineteen forties. https://newsprospect.com/the-ultimate-guide-to-pure-water-cleaning-with-a-water-fed-pole-for-solar-panel-cleaning/