Have a new BDB, trying to get the best water in it as scale is known to be a killer in these machines. Been reading a lot of material here on water. What I am confused about is why LSI calculators or the lamarzocco calculator (https://techcenter.lamarzocco.com/jsp/T ... ulator.jsp) both say the water is going to be too corrosive without any hardness. Ignoring the holy war on taste benefits of hardness in water vs not, I am curious is the rpavlis water (100mg/L potassium bicarb) _actually_ corrosive? I thought the issue was with low ALK stripping metal... Has any one here been running the pure pavlis recipe for 5+ years and has your machine survived?

grufromtheloo wrote:What I am confused about is why LSI calculators or the lamarzocco calculator (https://techcenter.lamarzocco.com/jsp/T ... ulator.jsp) both say the water is going to be too corrosive without any hardness.

The LM calculator is simplified advice and intended to be good enough for natural water. For homemade water it may often say corrosive when that's not really the case.

The LSI is a good but rough way of estimating whether water will tend to deposit or dissolve limescale. In any water that lacks calcium you will get negative numbers that are not necessarily indicative of corrosivity. For rpavlis water, you have good alkalinity to resist acidity and no chloride, sulfate, or anything that might promote corrosion. It was suggested by the late Dr. Pavlis (HB member rpavlis), a chemistry professor with professional experience related to water corrosivity, especially in copper and copper alloys. He used his recipe for years on his vintage Pavoni and Elektra lever machines.

grufromtheloo wrote:I thought the issue was with low ALK stripping metal.

rpavlis water has a healthy 50 mg/L (CaCO3 equivalent) alkalinity. One advantage is that it doesn't cause scaling, which means you don't need to periodically descale the machine. (Descaling solutions can strip the protective oxide layer from copper and brass boilers and fittings.)

Brian, first the BDB has stainless boilers so not as crucial need to have the protective oxide layer. But the other benefit besides no scale as Pat pointed out, is that it also will not have chlorides, which can cause corrosion even in stainless.

IMHO the long term effects of Pavlis water (which can be bicarbonate of either sodium OR potassium) is that you may get bored and want a new machine, before it suffers any damage from bad water.

-Peter

Thanks both. My Potassium Bicarb was delivered today and I made my first batch of Rpavlis Water. Emptied by boilers, reservoir and refilled. Will see how he straight rpavlis goes and may or may not try some epsom to bring up the GH, like perger water or the 70/30. Never thought I'd go down the water rabbit hole but here we are.

I've been using my lazy version of rpavlis water for about 6 years now, nothing goes in my machine(s) but distilled and KHCO3 (not meticulously added).
No signs of corrosion in either of my machines, LP romantica pro and Livia 90.

Distilled water is only quite corrosive when extremely pure, as would exist when it is being continuously completely replenished, as in a flowing stream. For example, the heavy 316 stainless steel process pumps, which I once applied in an ultra pure water application feeding a nuclear power plant, failed rapidly, looking like swiss cheese in a matter of months; they would have lasted for decades on slightly less pure water. When a quite small number of ions become present in the water the corrosion rate drops to very close to zero....

As regards to our applications, a boiler which is used continually just for steaming (as in an HX machine) will, when first started up with distilled water, corrode sufficiently to reach the point where the reaction essentially stops (very quick, all it needs are a few ions in solution to materially affect the equilibrium). By adding just a small amount of bicarbonate, the same is accomplished.

Inside the heat exchanger, the bicarbonate is essential, as it functions almost like a pipe, with a continuous fresh supply of water replacing the water and ions which go out with the brew. The fact that it is a very wide spot in the pipe will mitigate but not eliminate continuing corrosion. The same is true of a brew boiler or single boiler, which also will corrode unless there are always a supply of ions present.

I add just a pinch of KHCO3 to each gallon, it is not fussy. Sometimes I also recycle some water from the hot water tap (takes from the steam boiler) back into the reservoir to reduce the amount of bicarbonate, as it does build up (but does not scale as does tap water). This should also be enough ions to make the level sensors work in most machines.

My take on all of this often confusing subject.....

hankbates wrote:When a quite small number of ions become present in the water the corrosion rate drops to very close to zero....

Doesn't that depend entirely on which ion? If it's chloride ion I think the corrosion would get quite a bit worse.

Bicarbonate ion is special because of the way it buffers acidity. In pure water that's been exposed to air, the CO2 in the air dissolves and interacts with the water to form carbonic acid:
CO2 + H2O <--> H2CO3 <--> H⁺ + HCO3⁻
and of course that H+ is corrosive. If you add extra bicarbonate ion to the mix (as you do when adding KHCO3), it neutralizes H+ ions. driving the above reaction to the left. And a little does go a long way. Only 10 mg/L of KHCO3 added to a liter of pure distilled that is at equilibrium with atmospheric CO2 will raise the pH from about 5.6 to 7.2. That's about a 40 fold reduction in [H⁺] concentration.

hankbates wrote:I add just a pinch of KHCO3 to each gallon, it is not fussy.

Sounds like a good no-fuss recipe. A pinch (1/24th to 1/16th teaspoon) of powdered potassium bicarb would be around 200 - 300 mg, and if you add that to a gallon you're in the ballpark of 50 - 80 mg/L. (Dr. Pavlis usually recommended 100 mg/L, and said he sometimes used only 50 mg/L for brewing dark roasts.)

All bets are off when chlorides are present. This application was ultra pure water, and the ions coming into the water came from the metal and the reactions with dissolved gases such as O2 and CO2.