I imagine the water in ISO is distilled?
BTW, I have cleaned electronics and LEDs with just distilled water.
Some people even clean circuit boards in a dishwasher!
It is, and sure you can clean it with distilled water, absolutely, de-ionized would be a better choice. But it's not going to work as a solvent, which is what you need especially for resin from flux, or just from anything that burns up on the LEDs, finger oils, etc, water won't do shit. Also, soap will leave residue. Since ISO 91% is so damn cheap, why not? It works amazingly well, leaves no residue, dissolves next to everything that could be on the components, anything that could be causing a microcurrent short between pads, anything that could of burnt up on the LED, etc. It evaporates almost instantly, so no concern of having to wait for it to dry to use the light. All sorts of advantages, and it's everywhere for about the same price as a gallon of water. Just my opinion, I think the advantages outweigh water or soap so high that I am having a really hard time seeing why anyone wouldn't go that route. But to each their own!