Is de-ionized water better than RO water?

I have been cutting my tap water with store-bought distilled water for my AG batches up to now, but just bought an RO/DI system (latest toy ). Like all my new toys, I need to figure out how to use it (i think it's easy though).

It's a six stage system with the last stage being the de-ionization (DI) stage, which happens after passing through two stages of RO membranes. My question: is the DI stage necessary/significant for our purposes? It seems that a lot of people are confusing de-ionized water with distilled water. I just want to know if I need to use the de-ionization (DI) stage (one more thing to clean, maintain, repair) or if the RO stages are fine.

Thanks for any help.

De-ionizing filters are filled with a combination of cationic and anionic exchange resin stages. This is very similar to the salt-based cation exchangers used in water softening excepting that the resins are charged with H+ ions instead of Na+ ions. The anionic resin in the DI filter is charged with OH- ions. So when cations or anions in the water are intercepted by the resin, those ions are adsorbed to the resin and the H+ or OH- ions go into the water. Of course, when those ions get together, they form water. So unlike the salt-based exchanger, you aren't left with a dose of Na+ or K+ in the treated water.

Yes, this DI stage does remove much more of the ions remaining after RO. But the question is 'is it needed?'. Considering that we typically want certain levels of ions in our brewing water, the answer is NO. So, the extra DI stage is not needed for brewing use.

On a home level, a DI stage would probably be thrown out and replaced when its exhausted. This is because strong acids or bases are used to regenerate those resins and restore the H+ and OH- ion levels. For commercial systems, this regeneration is typically done back at the shop and replacement cannisters are delivered and exchanged with customers.

Yea, RO water is as close to no-ions as we need for brewing. You can just assume 0 on everything and work from there. The actual differences won't be noticeable by even the most discerning palates. The DI step is total overkill.

Also, make sure you have your ro and di stages identified correctly. I only say this because most 6 stage ro/di systems that I have seen (mine included) use one ro membrane and two di resin cartridges. Mine has a "T" after the ro membrane and before the di resin that goes to a drinking water container. The full 6 stages go to a salt water mixing station and a top off tank for the fish tank, otherwise I wouldn't use he di stages.

Edit: I was curious how the ro/di water would work for sparging, though. It might suck the sugars right off the grain. I'm a total newbie though so I'm getting a little ahead of myself here.

Easily_Distracted said:

Edit: I was curious how the ro/di water would work for sparging, though. It might suck the sugars right off the grain. I'm a total newbie though so I'm getting a little ahead of myself here.

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Interesting chemistry fact: the solubility of once substance (sugar) is not affected by the concentration of other dissolved materials (salt ions for instance). Also, sugar is stupidly soluble in water. In any case, it wouldn't be any better for sparging and it could really mess up your pH.

You don't want to brew with strait DI or distilled water. As mentioned before, you need some minerals in your water. You can use DI water to mix with your tap water. Or you could use RO water and brewing salts. Check out the A Brewing Water Chemistry Primer Thread. Explains in detain what you're wanting to know.

daksin said:

Interesting chemistry fact: the solubility of once substance (sugar) is not affected by the concentration of other dissolved materials (salt ions for instance). Also, sugar is stupidly soluble in water. In any case, it wouldn't be any better for sparging and it could really mess up your pH.

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Makes sense. That answers that. Thanks.

RO water is fine for sparging. Elevated alkalinity is the number one concern for sparging water and RO water has very low alkalinity. It will not mess up your wort or mash pH. Adding minerals to that volume of RO sparging water is a good idea if you have certain taste or fermentation goals, but you don't have to add the minerals to the sparging water before sparging with it. You can add those minerals directly to the kettle to produce the ionic concentrations desired.

In the case of the ionic strength of one substance affecting the solubility of another, that is somewhat true. But the first thing to recognize is that sugars in wort are at parts per hundred (aka: percent) concentrations and ionic concentrations in wort are at parts per million. You would NEVER have to worry about the concentration of ions in wort affecting the solubility of anything...they are too dilute.

Thanks for the responses. I figured RO water would be fine, and I will be building the water back up to target profiles.