Hello, I have a brand-new double boiler E61 machine.
The machine was a showroom model used for 'five shots'.
It came with a Quick Mill Flow Control Device pre-installed.
After running it for less than one month with '70/30' water (about 15 gallons), the flow control device looks like this:

After removing some of the deposit it looks like this:


The LSI for the 70/30 is slightly corrosive at about -0.7 at 212F (100C).
I measured my water as:

pH is 7.00
TDS is 90 ppm
Total alkalinity is 40 ppm
Hardness as calcium carbonate is 25 ppm

Could the water be the problem here?
The seller is saying the water is too corrosive, the 25ppm of calcium harness is too low and suggests increasing it to 70ppm.
What do you guys think?
Thank you!

Edit: typos

What is the chloride concentration in this water? How exactly did you make this 70/30 water? Staring with RO or distilled or just "water softened" tap water (which could have had a high chloride content to begin with)?

It's RO water with added pure Epsom Salt and pure Baking Soda as per the 70/30 water recipe found here:
https://s3-ap-southeast-2.amazonaws.com ... recipe.pdf

The tap water has a TDS 500 ppm, the RO measures around 30 ppm, the 70/30 measures about 90 ppm.

@Pressina, the Chlorine is the RO water is undetectable (.6 ppm in the tap water).

I now see you're asking for chloride not chlorine. Hmm, I'd have to research how to find that out...

I thought that 70/30 water was for brewing (IIRC, cupping originally), and not for espresso. I personally wouldn't use sulphates or a neutral pH water in a typical E-61 espresso machine.

Argh, that could very well be. I'll switch to rpavlis to be on the safe side.
I'm still surprised, could corrosion happen this quickly?

One thing I noticed is that there may be incorrect information about the corrosiveness of 70/30 water in this forum ' FAQs and Favorites > Good reference on water treatment for coffee and espresso':
Good references on water treatment for coffee/espresso

@homeburrero has a super informative post on all kinds of water that includes this bit about 70/30 water:

"70/30" water
A formulated mix proposed and used by 5 Senses Coffee in Australia - https://s3-ap-southeast-2.amazonaws.com ... recipe.pdf, and discussed here on HB: 70/30 Water . This recipe uses 70 ppm sodium bicarbonate and 30 ppm Epsom salt, hence the "70/30" moniker, and comes out to a hardness:alkalinity of about 25:42. There is no calcium hardness in this water and it should not scale. There is no chloride, and the sulfate is relatively low - the Larson-Skold comes out to about 0.6 so there shouldn't be a corrosion concern with this water.

When I enter the values into an LSI calculator, I get -0.6 not 0.6. And is therefore corrosive, no?

Edit: I was confused

Many in the light-roast community with "high clarity" burrs (98 HU, 64 MP, Bentwood, ...) run something close to 20 ppm GH, 80 ppm KH with the same ingredients and distilled or RO water. Your formulation is not far off of that.

Cybis wrote:When I enter the values into an LSI calculator, I get -0.6 not 0.6. And is therefore corrosive, no?

Larson Skold is not to be confused with Langelier Saturation Index (LSI). Larson Skold is a rough index for stainless corrosivity described here: https://corrosion-doctors.org/Cooling-W ... -Skold.htm. It involves the ratio of chloride and sulfate ion to alkalinity. It is related to the upper bound of the SCA core zone recommendation described in that post you mentioned: Good references on water treatment for coffee/espresso

Langelier Saturation Index is a very different thing, and it's really not correct to assume that a negative LSI is a corrosive water. A negative LSI indicates that calcium carbonate will tend to dissolve, and a positive LSI indicates that it will tend to deposit. People used to assume that you wanted a layer of calcium carbonate as a sort of 'protective scale'. That was always a simplification and is no longer widely believed. Calcium carbonate scale in an espresso machine is not uniformly deposited, and is porous, so provides poor protection. Given the trade-off between scale-prone (positive LSI) and scale-free water like rpavlis, the scale free water should be less corrosive in the long run because you don't need to periodically descale the machine, and descaling exposes the metals to harsh acids and can strip protective oxide layers from brass and copper. Copper oxides, unlike calcium carbonate, provide a thin and uniform protective layer. (I'm no corrosion chemist, I'm mostly repeating what I learned from the late Dr Pavlis here on HB.)

The LSI calculation for the 70/30 water would be off the scale negative. In fact you can't really do a proper LSI calculation because that water has no calcium, and a proper LSI calculation is based on calcium hardness. But that doesn't mean that it's corrosive.

As to what may have caused the copper corrosion in your pictures I'm at a loss. Perhaps the machine was given a descaling cleanup before being emptied for sale. Perhaps some of your RO is not that pure and much of the mineral getting though is chloride. Make sure you aren't using RO with minerals added for taste. That often means calcium chloride was added.

You might look around for de-ionized water. The refill dispensers at many Whole Foods sell de-ionized at the same price as RO, and it should be very pure - - less than a few ppm of mineral. You could also go with simple rpavlis style water - pretty much the same as 70/30 but without the Epsom salt. It theory it would be less corrosive because it has no sulfate ion.