Water quality & corrosion

[Brekel]

I have some questions about my water quality and what adjustments I should make.

I have recently bought my first HX machine, with a stainless steel boiler, after owning a Silvia for a number of years.

It was stressed to me that because minerals concentrate in the boiler as steam is drawn off, it is essential that I get a good water filter or the boiler would scale up. I think this was partly either a marketing ploy or lack of knowledge.

My average tap water parameters are:
Ca Hardness 25-30 ppm
Total hardness 28-35 ppm
Alkalinity 15 ppm
TDS 52ppm
pH 7.3

Chlorides 8-10ppm
Chlorine 0.5-1.0 ppm.

By my calculation, even at the boiler temp of 126°C the water would be a bit corrosive, certainly not scale forming. And when the machine is off & cold it would be quite corrosive. Different calculators give slightly different values, but all corrosive.

Is this level of corrosiveness likely to be damaging to the machine?

Before I did the LI calculations I started using a Brita jug as a temporary measure. This reduces hardness to 10ppm (or between 0-10, limit of test kit) Alkalinity down to 10ppm, pH 7.2. This actually makes the water more corrosive.

Should I add baking soda to my tap water to increase the Alkalinity?
And how about the Ca level?

[Brekel (original poster)]

Also, for interest I tested the water drained from the boiler. I normally empty and refill the boiler about every 2 weeks to avoid mineral concentration.

I'd been running the machine on the Brita water, and the boiler had gone from:
Hardness 10ppm up to 20ppm
Alkalinity 10pppm up to 30ppm
And the pH tested at around 9, or about 8 after equalising / shaking with air for a while.
So the minerals were a bit higher as expected but not bad, however the pH would have pushed it to the scale-forming range. Interestingly the calculated iequilibrium pH from the Alkalinity is much lower.

Any thoughts on the best way to go?

Thanks,
Brett

[homeburrero]

Nice post -- certainly looks like you've done your homework on this.

By my calculation, even at the boiler temp of 126°C the water would be a bit corrosive

Many LSI discussions lead you to believe that a highly negative LSI means that the water is corrosive, and that's a gross oversimplification. For corrosion risk it's arguably better to look at the alkalinity, sulfate, and most importantly the chloride numbers. Your chloride here is not bad (La Marzocco recommends it be below 30-50 mg/L and Synesso is very conservative about chloride and recommends it be below 15 mg/L).

Should I add baking soda to my tap water to increase the Alkalinity?

Your 15 ppm alkalinity here is lower than the oft-recommended 40 ppm ideal, but probably no cause for concern. If you are using a reservoir or a carboy tank then I think it might be worthwhile to spike it with a tiny amount of sodium or potassium bicarbonate (50 - 100 milligram per liter would be plenty).

And how about the Ca level?

Is fine, in my opinion. It has been argued to be necessary for taste, but the jury is out on that. Many people on this site use water with zero calcium and find that it tastes fine. Low calcium is a good way to assure low risk of limescale and/or calcium sulfate deposits in the machine.

Interestingly the calculated iequilibrium pH from the Alkalinity is much lower.

Be aware that the Puckorius pHeq is intended as a good value to use in making LSI calculations, but it is not the expected pH for water exposed to atmospheric CO2. For water with 15 mg/L alkalinity from calcium carbonate hardness your pH, after sitting a day or two in an open container, should settle in around 7.7. And the Puckorious pHeq is only 6.3. (Here's a nifty tool for estimating the pH of water exposed to air: http://www.aqion.onl/show_ph )

It was stressed to me that because minerals concentrate in the boiler as steam is drawn off, it is essential that I get a good water filter or the boiler would scale up.

That can be an issue, but not a good argument for trying to soften your already soft water. With non-scaling water like yours I'd recommend just managing that with the hot water tap: Using hot water tap to manage steam boiler water concentration

[Brekel (original poster)]

Thanks for the thorough and Informative response. I'll check out the links you included.