Thank you for that Veni. Not sure it really addresses the question though.
How about this excerpt from the article The “How To” Guide to Reef Aquarium Chemistry for Beginners,
Part 1: The Salt Water Itself by Randy Holmes-Farley
Quote;
"What Water to Use to Make Artificial Saltwater?
In addition to using a suitable salt mix, it is important to use suitably pure freshwater, both for making salt mixes and for topping-off for evaporative losses. The majority of experienced and successful reef aquarists in the U.S. appear to use RO/DI (reverse osmosis/deionization) to purify tap water. I also use it. A properly functioning RO/DI filter is always adequate to purify tap water that is otherwise drinkable. Many brands of these filters are available. Choosing one is not trivial, as they can have significant differences and the better units normally cost significantly more than stripped down models. It is beyond the scope of this article to detail all of the important attributes of good RO/DI systems, but they have been covered in previous articles. It is neither necessary nor desirable to add anything to RO/DI water or to any type of freshwater used to make a salt mix (or aquarium top-off to replace evaporation), unless you determine that after adding the salt, the water is deficient in something.
Reverse osmosis (RO) alone may be adequate in some cases, but is clearly not appropriate in others. In particular, if the local water company uses chloramine to disinfect the water, then the effluent from an RO-only system will contain substantial ammonia. If the tap water has copper at the high end of the normally encountered tap water range (> 1 ppm), RO alone may also be inadequate.
The use of tap water itself entails a number of concerns besides the presence of chlorine. First is chloramine, which does not dissipate after sitting around, the way many aquarists have done in the past for chlorine. It is now being added to many water supplies, and is much longer lived than chlorine. It also requires special treatments, not just the standard dechlorinating agents. Other concerns with tap water are copper (which often comes from your home's plumbing), nutrients (nitrate and phosphate) and alkalinity (which is not per se a problem, but can boost levels too high in some cases). In general, I recommend avoiding tap water. Sure, some folks use it and have fine aquaria. That does not, however, prove that any other tap water, even from a neighboring home, is suitable.
The best distilled water is perfect for our applications. Typical commercial distilled water is likely acceptable, as long as it has not been exposed to metals such as copper in condensers, pipes or holding tanks. Unfortunately, it is not easy to know the production history of distilled water, and testing with most copper test kits may be inadequate because they may not accurately read low enough to detect its presence.
Many aquarists use water provided by machines at grocery stores or from their local fish stores. Many of these are apparently reverse osmosis (RO) water. That is, again, likely okay, with the same caveats as for distilled water and RO water and in these cases it is unlikely that the aquarist can determine the proper maintenance of the filtration systems. Sometimes a chemical analysis can be provided by the supplier of such water, but frequently that is not available."
