Reverse osmosis after water softener – how to get correct TDS?

Water analysis, treatment, and mineral recipes for optimum taste and equipment health.
forbiddenbeat

#1: Post by forbiddenbeat »

I see this has been asked in various forms before, but not 100% sure what my solution should be. We just moved into a house that as an under-sink RO system, which puts out water of about 20-22 TDS. The house has an old water softener that we replaced with a dual tank unit, which has high TDS but is very soft.

For now, I have a tank machine and am adding in a tiny amount of tap water (which again, is soft) to get a TDS of about 50 so I don't corrode the boiler. But, this is a little tedious and I'd love to plumb the machine in eventually. Is my best option a bypass on needle valve that blends in tap water for me?

Nunas
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#2: Post by Nunas »

If you add the bypass from the city water to the product water out, you'll be adding in a small amount of whatever minerals are in the city water. If you add in water that comes out of the softener, then you'll be adding in mostly sodium. I've tried both and currently have the latter. Maybe my old taste buds are shot, but I can't tell much difference between straight RO, or either of the two foregoing. That said, I've never done side-by-side double-blind testing (too lazy :wink: )

I think your solution of adding in tap water isn't really the best (assuming your taste buds are better than mine). To the RO, I'd add in a mineral concentrate to turn my RO water into 'designer water'. A brief search here on H-B will turn up more recipes than you could read in one sitting :lol: .

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homeburrero
Team HB

#3: Post by homeburrero »

Santa Barbara water is hard, with high alkalinity, but also has high and variable chloride. Irrespective of whether you blend unsoftened or softened city water you will be blending that undesirable chloride along with the desirable alkalinity. If you get the blend right, on average you might be able to dial in 40 mg/L or so of alkalinity without getting the chloride much above 20 mg/L or so. But to my mind would not be worth trying. I'd just opt for a simple remin finishing cartridge after the RO if I were to plumb this system in.

Here's a link to a Santa Barbara water quality report - https://www.santabarbaraca.gov/civicax/ ... =220290%20 - that provides some averages and ranges for chloride and for alkalinity of the Santa Barbara water sources.

P.S.
To do the 'designer water' route with plumb-in, you could consider a 'flojet' like system where you draw from a large water container that you fill with your RO and spike with tiny measured amounts of mineral.
Pat
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pcrussell50

#4: Post by pcrussell50 »

When I lived in Santa Barbara, (we still own our house there as we are planning to come back at some point), I used RO to handle the chlorides. And the hardness was so high that I still got plenty of TDS even after the RO membrane.

Later, I switched to Pavlis water. I slept better at night that way.

-Peter
LMWDP #553

forbiddenbeat

#5: Post by forbiddenbeat »

homeburrero wrote:Santa Barbara water is hard, with high alkalinity, but also has high and variable chloride. Irrespective of whether you blend unsoftened or softened city water you will be blending that undesirable chloride along with the desirable alkalinity. If you get the blend right, on average you might be able to dial in 40 mg/L or so of alkalinity without getting the chloride much above 20 mg/L or so. But to my mind would not be worth trying. I'd just opt for a simple remin finishing cartridge after the RO if I were to plumb this system in.

Here's a link to a Santa Barbara water quality report - https://www.santabarbaraca.gov/civicax/ ... =220290%20 - that provides some averages and ranges for chloride and for alkalinity of the Santa Barbara water sources.

P.S.
To do the 'designer water' route with plumb-in, you could consider a 'flojet' like system where you draw from a large water container that you fill with your RO and spike with tiny measured amounts of mineral.
Great info, thanks! So our water softener also has a chloride filter. It's a dual-tank, dual-chamber system with chloride filtering media first, then water softening media. It sounds like it might be worth getting a pH meter so I can test our soft water. If the system is indeed working as intended, I'm guessing a needle valve to blend in should work.

forbiddenbeat

#6: Post by forbiddenbeat »

pcrussell50 wrote:When I lived in Santa Barbara, (we still own our house there as we are planning to come back at some point), I used RO to handle the chlorides. And the hardness was so high that I still got plenty of TDS even after the RO membrane.

Later, I switched to Pavlis water. I slept better at night that way.

-Peter
Thanks! If post-RO I'm getting 20-25 TDS, is that too low for an espresso machine?

The soft water does indeed taste bad, so perhaps I should just be mixing my own water. I was using distilled + Third Wave Water for a long time until we got the RO system.

Nunas
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#7: Post by Nunas »

post-RO I'm getting 20-25 TDS, is that too low for an espresso machine?
For the machine, no. I run at about 25 ppm TDS and also did on my HX. Neither machine had any problems. It takes very little conductivity to trigger the water level sensor. Anything else depends on your taste buds :D

At the risk of telling you something you already know, TDS is an overall measurement; it's only the hard-scale minerals you need to be worried about concerning operating the machine. For example, instead of the output from my RO system, I could use the output from my water softener which runs well over 250 ppm TDS, or I could use the town water, which runs about the same. The difference is the town water is full of hardness minerals while the water softener output is mostly sodium. Sodium is soft and does not produce scale. Our town water would probably KO the machine in a few months.

forbiddenbeat

#8: Post by forbiddenbeat » replying to Nunas »

Thanks, and yep, aware that TDS isn't a measurement of hardness. Mostly I was concerned about alkalinity and dissolving the boiler, so I'll test the pH of the RO water and if it's good, leave it alone.

Nunas
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#9: Post by Nunas »

Sorry, I misunderstood your concern. My RO water consistently tests at about 7.0, using an aquarium test pen. I've used that water in many coffee makers, several semi-auto espresso machines, and in five electric kettles-two stainless and three plastic. The stainless ones have unexposed elements and the plastic ones have exposed elements. I also use it in my lever machines, a Caravel and a Riviera. I've never seen a trace of corrosion or leakage anywhere. I know this all flies in the face of the usual advice, that RO water needs to be buffered. But, that's my experience, YMMV.

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homeburrero
Team HB

#10: Post by homeburrero »

forbiddenbeat wrote:So our water softener also has a chloride filter. It's a dual-tank, dual-chamber system with chloride filtering media first, then water softening media. It sounds like it might be worth getting a pH meter so I can test our soft water. If the system is indeed working as intended, I'm guessing a needle valve to blend in should work.
I think what you have there is probably a standard chlorine/chloramine charcoal or carbon block filter. Those will reduce the low level of chlorine to near zero, but will not reduce your chloride at all.

forbiddenbeat wrote:Thanks! If post-RO I'm getting 20-25 TDS, is that too low for an espresso machine?
That is more than enough to make your water sensors work. But is likely a little low in alkalinity (alkalinity is a measure of acid-buffering capacity of the water). Most water advice, including the recent SCA water quality handbook, advise that espresso machine water have alkalinity at or above around 40 ppm (in units of CaCO3 equivalence). Your 20-25 ppm RO water with is most likely below that. If some of that 20-25 TDS is comprised of chloride ion, then having good alkalinity numbers is even more important. (Chloride ion can catalyze corrosion in steel and especially in copper/brass boilers and fittings.)
forbiddenbeat wrote:It sounds like it might be worth getting a pH meter so I can test our soft water.
Or better yet, use a drop titration kit to measure your alkalinity. Titration kits that measure 'KH', 'carbonate hardness', or 'temporary hardness' are alkalinity test kits. The API fishcare KH kit that you can buy online or at pet stores is one simple and inexpensive way to do your alkalinity tests.
Pat
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