Hard vs. Softened RO Feed water...

[ebstauffer]

I recently purchased a 3-stage RO system from @Buckeye_Hydro (absolutely fantastic company to deal with) and am wondering if there will be an appreciable difference in membrane life or output water quality if I feed it with softened water rather than unsoftened muni water. Here in Indianapolis our water is around 300 - 350 TDS. When I ran water to my garage/shop/non-spouse-place/brewery I ran both softened and unsoftened so while it wouldn't be a huge effort, it would be significantly easier to not to replumb (it's currently fed with unsoftened). The RO water is used only for brewing and "building" Gerolsteiner mineral water which I enjoy with my brown spirits. I brew maybe 20 gallons a month so not that much RO water.

 

[day_trippr]

This is definitely a Russ @Buckeye_Hydro question, but iirc he has mentioned if you have a softener it's usually better to use the output of that as input to the RO system vs using the pre-softened supply.

That said, my well runs around the same TDS as your muni supply with an RA over 200, and have been using that as my RO system feedwater for years - because we don't have a softener...

Cheers!

 

[mabrungard]

Actually it’s already been answered in articles published on RO systems by Zymurgy. Softened water can significantly enhance the longevity of RO membranes.

 

[ebstauffer]

Actually it’s already been answered in articles published on RO systems by Zymurgy. Softened water can significantly enhance the longevity of RO membranes.

I certainly understand that it does lengthen RO membrane life, just trying to determine if the ends justify the means for my use case (< 300 gallons per year). I suppose if I have some pex & fittings laying around I should just do it. That'll be another few hours filled that I'd otherwise be asking myself, "what should I do for the new few hours". Thanks COVID19..

 

[mabrungard]

With respect to water quality, the sodium content of pre-softened RO is higher than the unsoftened RO. But it’s still well within the ‘insignificant’ for brewing level.

 

[ebstauffer]

With respect to water quality, the sodium content of pre-softened RO is higher than the unsoftened RO. But it’s still well within the ‘insignificant’ for brewing level.

I had intended to use my RO water for calibrating equipment like my electronic hydrometer and table-top refractometer. Is my RO water (about 9 ppm tds according to the meter assuming it's calibrated correctly) "good enough" for that or should I have invested in a ion exchange column as a 4th stage. And that being said, what ions generally stick to the resin in that type of column?

 

[Vale71]

Unless your hydrometer and refractometer can measure to the 5th decimal place then you can use straight tap water and it won't make any difference.

 

[ebstauffer]

Harumph. Once again unnecessarily sweating the details. Thanks for reminding me of that.

 

[Buckeye_Hydro]

It is true that hard feedwater can lead to the premature demise of an RO membrane. The dissolved minerals (primarily Ca and Mg) in hard water form scale that most people are familiar with. The scale can form inside the RO membrane. When you "scale" a membrane, purified water production slows, and often the quality of the RO water declines.

In commercial applications where 1) the RO membranes are larger and can get quite expensive; and 2) membranes are commonly plumbed in series (concentrate from membrane 1 feeds membrane 2); and 3) less then high performance of the RO system adversely affects commercial operations; we routinely specify water softeners. Where the RO system is expected to be online at all hours of the day, we typically specify twin tank alternating softeners - these softeners have two mineral tanks (tanks containing water softening ion exchange resin) that can produce soft water 24/7 without interruption.

That said... the residential-scale RO systems used by homebrewers use relatively inexpensive membranes (~$30 to $50), are rarely configured with membranes in series, and are typically configured with a lower recovery (more of the feedwater ends up as concentrate) than commercial systems. The user with hard water is essentially making a trade off - he's accepting lower recovery and or shorter membrane life (higher operating expense) to avoid the expense/trouble of using softened water.

The choice is up to the user of course. If the only consideration was the welfare of the RO membrane and the RO system... it is a no brainer: always use soft feedwater.

Russ