Deionized or distilled water simply means "pure" water. But from a chemical standpoint, water just ain't natural in that pure state. Water wants to get dirty. Therefore, pure water is far better for de-salting reels than well or tap water.
Here's the reel-cleaning method I use: Save a plastic bottle that sprays a fine mist (the kind window cleaner comes in). Clean that bottle well. Put about 2 inches of distilled or deionized water in the bottle and spray your salty reels when you come in from fishing. The fine mist will not drive salt into the reel, and the ultra-pure water dissolves salt fast.
Spray with water, wipe with a clean cloth, and then spray again and wipe. Allow the reels to dry for an hour or so; then wipe with a silicone gun cloth or a rag with a little oil sprayed on it.
Capt. Ken Roy
Crystal River, Florida