I recently bought my first high-end espresso machine, a Lelit Bianca, and want to use the best water recipe I can to protect the machine long-term. I have read The Insanely Long Water FAQ multiple times along with studying other sources.

Background: Location = NYC; Cannot plumb-in the machine; I could remineralize the soft tap water but for consistency I plan to remineralize distilled water with baking soda (sodium bicarbonate) and Epsom salt (magnesium sulfate); only make 2-3 milk drinks (mainly cortado & flat white) per day; willing to sacrifice the marginally better taste of 100:50 coffee water for a "boiler safe" water.

Goal: Minimize overall damage (scale & corrosion) to the machine over the long-term without descaling.

Problem: I initially thought I would use water in the 90 hardness 50 alkalinity range (gh:kh = 90:50) and perform preventative descaling 1-2 times per year. The problem is that Lelit & 1st-Line Equipment (where I bought the machine) highly recommend not descaling the machine at all or having it done professionally if it is truly needed. That is an issue for me as I would need to rent a car to take the machine out to NJ to have it professionally descaled making that cost prohibitive on a regular basis.

With that in mind, I read the Insanely Long Water FAQ many times (big thank you to Jim for putting that together) in search of a water recipe that would prevent ever needing to descale the machine. This leads me to consider a lower hardness higher alkalinity recipe, say 40:60, that in the FAQ is referred to as boiler safe and similar to formulas is used in commercial machines to minimize scale. If I understand the math correctly, even at a steam boiler temperature of 257f/125c the 40:60 water should produce almost no scale. That seems like a good solution in the steam boiler and even in the brew boiler at 198f/92c the LI shouldn't drop below -.5 and should not be corrosive. My concern is when I shut the machine off later in the day and it cools down to room temperature of 70f/21c, the LI should drop below -1 and even edge towards -1.5. Is corrosion going to be an issue in a dual stainless steel boiler machine, like the Lelit Bianca, at these levels at room temperature? The FAQ is incredibly thorough on scale and I understand the concept but I had more trouble getting my head wrapped around corrosion. Will the 60mg/l of alkalinity prevent corrosion even at LI -1.5? Does the water cooling down reduce corrosivity enough?

This whole exercise has felt like a balancing act of hardness, alkalinity, and temperature that can be solved to maximize effectiveness at one set of hardness/alkalinity variables but as temperature changes the same mixture can have different effects. But alas, I guess that is why this is such a difficult question to answer and a never ending discussion topic.

Thanks in advance,
Rob

Main Question: Is a 40:60 water recipe a good boiler safe solution that will not cause scale or corrosion within a stainless steel dual boiler machine and never require descaling?

P.S. Yes, I know many people recommend potassium bicarbonate as a preferred buffer agent instead of sodium bicarbonate but for simplicity's sake I want to start with baking soda and adjust from there.

My $.02 is you were on the right path to begin with. My goal is similar to yours, but I have dropped the goal of never descaling. I just want my gear to not die from scale and to enjoy maximum taste.

ILWF talks about the descale process occurring at a known level of scale, (5 grams). I am working on the numbers to determine when to perform the descale process in two hours. Section 4 lays out what to do, and it's really not a big effort.

There are a number of other vendors/retailers who make the same statement to never descale. La Marzocco for example, doesn't call out any descale process in their maintenance info, but they list replacing the pressure valve annually. I can imagine vendors/retailers have stories to tell that validate this suggestion. However, we're into the details a bit further than the average customer and water chemistry is mostly settled science.

I have the same very soft upstate NY reservoir water here in Westchester County as you do in NYC.

I first discovered that supplementing that tap water with half strength RPavis (potassium bicarbonate) water resulted in better tasting espresso and no chance of scaling. I more recently began to use half strength third wave water from their recipe and my mixing bulk ingredients. Taste wise both are pretty comparable. I'm sticking with the 3rd wave formula (1/2) for now and I will have no scale issues and pretty optimal taste. I found no need to buy distilled with our tap water being so soft and very low in chlorides.

Thanks NYC-Rob for taking the time to craft a very complete, well written post. And welcome to HB!

A few comments FWIW

NYC-Rob wrote:I read the Insanely Long Water FAQ many times (big thank you to Jim for putting that together)

+1

The scale rate calculations in the FAQ are well done and well explained. But it's worthwhile to note that the FAQ was written for natural water and not so much recipes built on Epsom, bicarbonate, etc. The Langelier calculation, for example, is based on calcium carbonate chemistry, which is fine for natural water with hardness that is primarily calcium. Your Epsom + bicarbonate recipe is all magnesium and no calcium. The chemistry for magnesium precipitation (as MgOH, MgCO3, and possibly MgO) is more complex than limescale (CaCO3) deposits, and we have no simple LSI-like equations for that. At typical coffee water pH values it's a safe bet that magnesium is far less scale prone than calcium, and reports from users of Matt Perger's 100:50 recipes are not reporting scale problems. You will, however, need to take care to avoid concentration of the steam boiler water as discussed in the Insane FAQ. (More on that can be found here: Using hot water tap to manage steam boiler water concentration)

Having said that, I think that your choice of a 40:60 (GH:KH as CaCO3) mix is a good one. No chance of limescale (because it has zero calcium) and keeping the Epsom low is in my opinion good because the water would have less sulfate and less magnesium, making it closer to natural water. The 60 mg/L is a good choice to help avoid corrosion (The SCA water quality handbook and other texts advise that you keep it above 40 mg/L).

NYC-Rob wrote:My concern is when I shut the machine off later in the day and it cools down to room temperature of 70f/21c, the LI should drop below -1 and even edge towards -1.5. Is corrosion going to be an issue in a dual stainless steel boiler machine, like the Lelit Bianca, at these levels at room temperature? The FAQ is incredibly thorough on scale and I understand the concept but I had more trouble getting my head wrapped around corrosion. Will the 60mg/l of alkalinity prevent corrosion even at LI -1.5? Does the water cooling down reduce corrosivity enough?

If you do an LSI calculation by the book based on low calcium hardness your LSI is much lower than that. Beware that a low LSI is 'aggressive' but not necessarily corrosive, and is often meaningless when evaluating these very unnatural waters made from recipes. Perhaps the most machine healthy recipe out there is the rpavlis water with zero hardness and 50 mg/L alkalinity. LSI for that and other zero calcium water is off the chart low and can't even be calculated (and is meaningless). In your case the corrosion risk is low based on the alkalinity and zero chloride. In theory it's possibly improved by using less Epsom because of the sulfate contribution to corrosion risk.


P.S.
Many water treatment old timers believe in the idea of 'protective limescale'. The idea was that a light coating of scale helped protect against corrosion. Modern advice that I'm reading in water treatment articles, as well as advice from the late Dr. Pavlis on this forum, is that the limescale layer is porous and not really protective. Then if you add in the issue of periodic descaling, which may strip oxide layers (which are protective) and expose metals to harsh acids, I think the balance tips in favor of using non-scaling water for optimal machine health.