Not sure how, Dean.

Reverse osmosis does clean or concentrate or purify liquids but not, AFAIK, to the standard of deionizing.  RO is used to desalinate sea water to give drinking water, it is used to remove water from orange juice to make concentrate, etc.

Your average big CO2 laser is just about the worst possible design from a corrosion point of view. Aluminium, steel, copper, brass and stainless sit in the same system and sometimes connected to each other.

The laser uses deionised water, with very low conductivity = high resistivity, to block the electric currents that flow from one metal to another causing corrosion.  The higher the resistance of the water the lower the current and the less the - usually aluminium - corrodes. 

Inhibitors also help by coating the sufaces and again reducing the electric currents.

It is worth investing in a small conductivity checker and changing water when it needs it even before a service.

Just a little low conductivity water can be disastrous.  Do check the deionizer when you refill your system.  We have found that a deionizer exhausted before the tank was full and put tap water in the tank. High conductivity = fast corrosion.  We bough the conductivity meter soon after that.

So, top quality DI+inhibitors are your best bet.

Neil