So why not distilled water?

I have no plans to use distilled water and I know why pure H2O is no good for fishkeeping. I'm just wondering, is there a reason why people use RO/DI water instead of distilled, other than convenience and cost? I'm pretty sure it's just a matter of distilled being more expensive and harder to find, and RO/DI is much easier to obtain either from a store or an in-house filter, but I want to be sure.

 

I'm not sure it matters in most contexts either, aside from cost.

 

RO is not exactly the same as distilled. Distilled water is pure H2O, RO water still has some things in it. E.g. chloramine can't be filtered out by RO units.

But both have in common that Nitrates, GH and KH are virtually zero.

The price is definitely the biggest difference. I paid 2€ per 5l for distilled (easy to obtain in hardware stores here) but only 50,- for an RO unit big enough for my purposes. So longterm RO is the way to go, though there are some things to keep in mind, not necessary with DI.

 

RO is not exactly the same as distilled. Distilled water is pure H2O, RO water still has some things in it. E.g. chloramine can't be filtered out by RO units.

But both have in common that Nitrates, GH and KH are virtually zero.

The price is definitely the biggest difference. I paid 2€ per 5l for distilled (easy to obtain in hardware stores here) but only 50,- for an RO unit big enough for my purposes. So longterm RO is the way to go, though there are some things to keep in mind, not necessary with DI.

Don't RODI units usually have prefilters to remove those remaining contaminants? Chlorine in particular will quickly destroy both RO units and mixed bed resins.

 

Here in my country they don't, as chlorine and chloramine (and a lot of other stuff) are removed by the supplier before the water goes into the system, most users of RO units here on the Forum report chloramine doesn't get filtered out.

 

Don't RODI units usually have prefilters to remove those remaining contaminants? Chlorine in particular will quickly destroy both RO units and mixed bed resins.

They should if they're setup and maintained properly.