The Effect of RO Water On Scale

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

Postby RoastedRob » Dec 03, 2018, 8:38 pm

I recently purchased a new espresso machine for my business. 2 months ago I noticed some scale build up around the hot water faucet. I brought it up to my water filtration company. They did some testing and believe that the membranes on the RO system, which we need due to the crazy hard water in NM, have been failing due to chlorine in the water system. They ordered new membranes and will install as soon as they arrive. I myself bought an HM Digital TDS meter and tested the water. It came to a TDS level of 600+ppm! I am now seriously concerned about scale build up inside my brand new machine. The company believes the RO water will eat away any scale build in time as it's only a few months worth of scale. I believe I've heard this before as well.

How true is this? If not are there any other suggestions on breaking down the scale that has built up?

Rob

Nunas

Postby Nunas » Dec 03, 2018, 8:47 pm

Yes, it's true; at least one manufacturer and several articles have been presented on this aspect of RO water. Indeed, some argue that pure RO water (less than 5 ppm TDS) will eventually leach out some metals in an espresso machine. Maybe so. In any case, good coffee needs a small amount of hardness in the water. After reviewing many recommendations from espresso machine manufacturers, I've settled on 25 PPM with a blending valve on my RO). Last I looked I have zero scale. Also, my electric kettles look brand new. I guess it depends on how long you've been running with the defective membranes in your RO. If it is badly scaled, you might want to use a chemical descaler. Wow, 600 PPM...that's some hard water! When we travelled a lot in our motorhome the hardest I encountered as about 500 ppm and the taste was like chalk. The locals would joke that one could hammer nails into the water.

blkswn

Postby blkswn » Dec 03, 2018, 8:55 pm

RO water does remove scale, albeit, at what cost I do not know. I have two examples where this worked.

1) I noticed some scale build up in my GS3 from a prior owner who used brita "filtered" water. I ran about 6 gallons or so by running the hot water wand and small flakes of scale did come out with each on/off cycle. Do remove the water dispersion filter/screens to avoid clogging those tiny holes. Little tiny pieces of scale still come out occasionally when I flush out the steam boiler even with my properly treated water.

2) In an electric kettle I have, it built up visible signs of light scale formation after one fundraiser event. I left the kettle as is and boiled RO water in it a few times for pour overs back at home to see if it removes the scale, and surprisingly it removed all of the scale residue.

User avatar
homeburrero
Team HB

Postby homeburrero » Dec 04, 2018, 2:12 am

RO water, even if equipped with a standard remineralizing cartridge, will tend to remove calcium carbonate scale over the long run. One can do a Langelier Saturation Index calculation, plugging in values for temperature, alkalinity, hardness, and TDS to come up with a number, which if negative predicts that the water will dissolve scale, and if positive that it will deposit it. For just about any RO system that produces water below around 40 ppm on a TDS meter you can bet that an LSI calculation would come out with a negative (dissolves scale) value. See Jim's Insanely Long Water FAQ (here) for scaling rate and LSI calculation info.

At 600 ppm, I hope they get those new membrane filters in fast, and are doing something to address that chlorine problem. Your TDS meter may come in handy to watch out for membrane failure in the future.

If you aren't already using a remineralization cartridge with that RO system, I think that's something you should look into adding. It may help with the coffee taste, but most importantly it would raise the alkalinity of the water, making it less corrosive and better for the long term health of that nice machine you have.

P.S.
A remin cartridge is the simplest solution. But some high-end espresso systems use formulators or bypass blending to allow a custom adjusted mix of minerals. These are more expensive and more complicated to set up and monitor, and in some cases (e.g, water with high silica or high chloride), bypass blending may not be a good option.
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

RoastedRob

Postby RoastedRob » Dec 05, 2018, 3:25 pm

Thank you for the input everyone.

So it appears that some of you have experience with RO dissolving scale buildup. I started noticing the scale around the hot water faucet about 6-8 weeks ago so hopefully it hasn't been going on for long. My question is at what TDS do you recommend we set it at and for how long to dissolve the scale? Do we just run it as usual?

I assume running it at straight 0 will cause probe level failure.

I had them empty out the RO reservoir and pour in some RO water from their shop. As of today it's at 70ppm as it's still mixing with some of the hard water in the system. We are getting everything changed out today though.

As homeburrero mentioned, they are using a bypass blending method to hit the 150 TDS recommended by the SCA. Maybe in the long run for the life of the machine we should shoot for lower TDS?

I believe they are adding a carbon filter before the RO to help with the chlorine. We've had some water problems recently here which is why the chlorine has been added to the city water. It has caused a lot of problems but I am very relieved that my brand new machine can be helped back to normal and I can sleep at night now. haha

User avatar
homeburrero
Team HB

Postby homeburrero » Dec 05, 2018, 6:25 pm

RoastedRob wrote:My question is at what TDS do you recommend we set it at and for how long to dissolve the scale? Do we just run it as usual?

If it were me, I'd dial it down til the alkalinity was around 40-50 mg/L. Your RO people probably have a kit to test that. You can test it yourself with an inexpensive kit sold online and in pet stores: API GH & KH Test Kit. If the espresso tastes good at that level I'd just stick with it.

RoastedRob wrote:I assume running it at straight 0 will cause probe level failure.

Even at zero bypass I think your level probe will work fine. They don't require much; a conductivity meter reading of 5-10ppm should be plenty, and even if you have a very efficient RO, given the high TDS of your incoming water you should have that much conductivity at zero bypass. The downside of very low TDS would be that it would also be very low alkalinity and over the long run may cause corrosion. Over the short run, assuming you do have scale deposits built up inside your machine you don't need to worry about low alkalinity and corrosion.

RoastedRob wrote:... they are using a bypass blending method to hit the 150 TDS recommended by the SCA. Maybe in the long run for the life of the machine we should shoot for lower TDS?

That SCAA recommendation of 150 TDS should not be taken too seriously. For one thing, the SCAA did their measurement using a TDS meter calibrated differently than yours. If they had used an HM digital meter with a calibration factor of 0.5, their 'ideal' water would have read more like 115 - 120 ppm. I think the best approach is to adjust the bypass so that the alkalinity is at least 40-50 mg/L, then maybe bump it a little higher to get the hardness up in the 50 - 80 mg/L range if you think that improves the taste of your espresso, AND if the hardness and alkalinity numbers are still OK with respect to scale deposits. (The (FAQ) that I mentioned earlier can help with that, and is also referenced in the water guidance in some of the Kees manuals.)

RoastedRob wrote:I believe they are adding a carbon filter before the RO to help with the chlorine. We've had some water problems recently here which is why the chlorine has been added to the city water. It has caused a lot of problems but I am very relieved that my brand new machine can be helped back to normal and I can sleep at night now. haha

Good to hear that.

P.S. Are you running a coffee shop? I don't think I've ever seen a Kees Spirit in a New Mexico shop, would be fun to visit if you're agreeable to sharing your shop's name and location.
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

RoastedRob

Postby RoastedRob » Dec 06, 2018, 8:54 pm

Homeburrero...I mentioned all the alkalinity and other conditions to my water company and we're going to be shooting for these perimeters. I just checked it today after all the filter changes and it's still at 47ppm so hopefully that'll be coming down soon.

And yes I do have a coffee shop here in Artesia, NM. Right now we're working on adding a roastery and bakery to our current building. My original machine when we opened 13 years ago was a Kees Mirage. So I just this summer purchased a Spirit and we're still the only ones I'm aware of that have an KVDW machine in NM. The name is currently The Jahva House but with the roastery and bakery additions I've decided to rebrand. But we're the only coffee shop in Artesia so you can't miss us.

Rob

User avatar
homeburrero
Team HB

Postby homeburrero » Dec 08, 2018, 2:36 pm

RoastedRob wrote:And yes I do have a coffee shop here in Artesia, NM. Right now we're working on adding a roastery and bakery to our current building.

High end shop in Artesia - Cool! I've added you to my must-visit list.
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h