DI water is only used to cool lasers where the lamp electrodes must be wet, ie non-conductive water. Other lasers use either water with a oxygen inhibitor cartridge, filtered water, or water plus glycols. In some cases a corrosion inhibiter may be added to anything but deionized water. Much of this depends on the materials used in the baseplate and the plumbing.
I spent three months in a lab once dealing with the effects of a Post-Doc, who added fresh DI water every day to three lasers with aluminum baseplates. I milled new baseplates, remounted/realigned the lasers, and replaced all the chiller pumps. He had a lamp pumped laser in the past and thought that the new diode pumped lasers should also use DI. At least I got paid.
Steve