Don’t use the water from your steam boiler

A few days ago, Dutch barista Zeeshan Malik posted a question to my YES or NO Instagram Q&A experiment. (Early YES or NO results:  most questions submitted haven’t been well-suited to a yes-or-no answer.  Unless it gets a little easier, YES or NO will probably be short-lived.)

Zeeshan wrote:

Can I use the hot water dispenser on my 3-group commercial espresso machine for regular tea/filter coffee brewing (assuming correct temperature) without any negative impact on flavour?

I answered “NO” because the typical commercial-espresso machine’s steam-boiler water is alkaline and packed with minerals.  When used to brew tea or coffee it results in a chalky taste.  When added to an already-brewed espresso to make a drink such as an americano or long black, the effect is less pronounced, but the steam-boiler water is still usually not the best choice.


Why is the water so bad?


Every time a barista steams milk, the steam is pure water vapor, free of minerals.*  Any minerals that had been dissolved in the vaporized water remain in the liquid in the boiler, increasing the water’s mineral concentration.  After each steaming, the boiler refills with a bit of mineral-laden water, continuing the process of removing pure water (vapor) from the boiler and replacing it with mineralized water.  (I prefer not to complicate this simple explanation with a discussion of scaling, corrosion, or milk being sucked back up a steam wand.)

*I’m neither a chemist nor a physicist.  Perhaps a reader who is one can tell us if there can be, in fact,  trivial amounts of minerals in the steam.


See for yourself


If you’d like to test this idea, find an espresso machine that has been used to setam tens of thousands of milk beverages since the last time its steam boiler had been drained.  The taste defect will be most obvious when brewing tea, less obvious when using the water to brew coffee, and least obvious in an americano.


Of course, if the water feeding an espresso machine is extremely low in mineral content, it will require a greater number of milk-steaming episodes for the taste defect to become apparent.  As well, machines with a hot-water tap fed by a mix of “fresh” water and steam-boiler water will produce noticeably tastier tea or coffee, perhaps with little or no noticeable taste defect, depending in part on the mineral content of the feed water and the boiler’s past volume of milk steaming.

Regardless of the quality of steam-boiler water, overuse of an espresso machine’s hot-water tap may decrease steam-boiler pressure too much during busy service times.  If the steam boiler refills with cold water too fast for it to maintain effective boiler temperature (and therefore pressure), steaming power will be inadequate.

An easy problem to solve


I cannot count the number of times baristas have served me an undrinkable, chalky cup of tea brewed with steam-boiler water.  This is a particularly common problem in countries where cafes typically serve espresso but not filter coffee, as cafes with batch brewers or pourover kettles typically use those for tea and americano water. I hope this post helps decreases the use of steam-boiler water to make beverages.  I recommend quality-oriented cafes, even in espresso-dominated markets, keep a temperature-controlled kettle on hand for tea and americanos.  It’s a wortwhile, small investment.


Thoughts?  Experiences you’d like to share?



*The skull and crossbones is just for fun, not meant to imply your steam-boiler water is poisonous. 

** I wish we didn’t have to have such disclaimers in modern society. 

28 thoughts on “Don’t use the water from your steam boiler

  1. Interesting…

    While I’m not an expert, if any one would had posed this question over beers in my presence – my answer would match yours – “NO” but for different reasons…

    Chinese and Japanese tea do require some minerals in the water. Connoisseur will sometimes go out of their way to heat the water in iron kettles for this reason alone – (there are kettles and then there are kettles). It is said that Oolong in particular benefits from the infuse of minerals and slowly heating water in traditional cast iron kettles does affect the way the water tastes – making it ideal (experts will say) for Oolongs and many other teas.

    Now, not to say that these are the same minerals found inside my boiler (as you have calcium forming within your boiler not to mention the walls of your boiler made of different metals) – but the very first reason to pick “no” is “water temperature”. Each tea require a very different temperate (and time) to brew the tea. The hot water from our boilers come at one set temperature and I’m certain (although some one should test) that each machine will give you a different temperature which will not match the tea you are serving unless you are very lucky (or only have one tea that you picked for that purpose).

    So – while I agree with Scott’s answer – also take the temperature to brew your tea as the basis for that “no”… if we are going to make the best coffee, serving burnt tea is no way to punish the rest of our guests…


    • Hi Ramsesm,
      I didn’t address temperature because Zeeshan’s original question noted “assuming correct temperature” and I wanted to focus on the quality of the water, not on the details of tea or coffee extraction temperature.

      As well, regardless of the ideal mineral content in water for brewing various teas, the problem is that the mineral content in most steam-boiler water becomes very concentrated over time– far more concentrated than what I would consider appropriate for any tea.

      I get the “seasoning” of clay gong-fu tea pots, but I’d personally avoid preparing tea in a cast-iron tea pot, as the pot may leach some iron into the tea. Opinions will differ, but I see that at best as a low-quality form or dietary iron, at worst dangerous for some people.

      Thanks for your comment.

  2. Seeing as there’s only one boiler, does this mean the brew water from a heat-exchange (HX) machine is unsuitable for making espresso?

    • Hi Jonathan,
      No; the steam water is segregated from the brew water. The brew water comes “fresh” from the plumbing, through the heat exchange tubes, and into the group head. It never touches the steam-boiler water. The steam boiler water surrounds the HX tubes and heats them.

    • Nick,

      The goal is not to find a way to use the steam water, it’s to make good coffee and tea. Your proposed solution would take a lot of effort, require hours each day to drain, refill and reheat the boiler, and would use more energy. Why not just buy a kettle?

  3. I was recently on an origin trip to Thailand and it’s become quite the spot for specialty and non specialty shops alike. I noticed most shops were using water from the steam boiler, thus creating cups of coffee or tea with that chalky flavor. It’s a bummer to see espresso manufacturers not solve this problem, especially when it comes to elevating better coffee spots internationally, more specifically, in coffee producing countries. It’s somewhat of a challenge for certain countries to get well performing machines, therefore, many seem to rely on the steam boilers for hot water.

    Maybe the manufacturers of espresso machines can develop something aside from the steam boiler that is still integrated in the machines? I’d love to hear what others have in mind!

    • Aaron,
      It’s certainly doable– the Decent we’re developing will have a hot-water tap with freshly heated water, delivered at whatever temperature and dose you ask for. So I suppose such improvements will be copied and eventually become the norm.

      In the meantime, I wouldn’t wait for machine manufacturers, I’d just go out and get some temperature-controlled kettles. It’s a pretty simple and cheap solution.

  4. Surely an obvious answer is to use a dual boiler espresso machine, like a La Marzocco, which has one tank for steam and one that is used as a heat exchanger for espresso? The hot water outlet coming from the later?

  5. Does this problem remain when the steam boiler water is being used repetitively during the day?
    My parents use this water for pre-heating cups, brewing americanos, brewing herbal and black teas and for some other random things. This means the steam boiler gets refilled a couple of times every day. Another company I know uses the water to polish wine glasses and cutlery. Of course it’s not a complete refill, but over time I guess the mineral content would remain a steady bit higher than the line water, but not to excessive amounts.
    I’m not saying it’s a better solution than having a designated water tap for americanos and tea, since that would give more control on the TDS of the brew water. However, I do believe the taste effect would be too small to allow for an additional investment.

    • Hey Jelle!!
      I suppose it depends on their water chemistry and how much they’re dispensing from that tap.

      I have to take issue with your last statement, though. Somehow most of these comments seem to assume that having a kettle is either burdensome or expensive. A temperature-controlled kettle will cost them 50 Euros. And it will help preserve steaming power, offer temperature control (I haven’t harped on this yet, but no one should be making americanos with near-boiling water), and provide guaranteed proper water chemistry. A kettle is a trivial investment, so why is there any reluctance to buy one?

      Finally, next time you’re at your parents’ cafe, I suggest doing a blind taste test of some green tea brewed at 73c (Japanese) or 80c (Chinese), using the boiler water and water from a kettle. (Please fill the kettle with the same water that feeds the espresso machine). A proper test is better than us assuming how good or bad the boiler water is for tea.


      • Thanks for the elaborate reply. To be fair we did do some tests with americano water temperature and try to use a different temperature for different coffees (even the difference between 75 and 80 degrees is very noticeable in the drink).
        I’ll definitely give the experiment a shot. I still have some sencha from my trip to Japan so those will come in handy.

      • So I finally got around to visiting my parents again and making some Kabusecha tea. World of difference: tap water brought to 64C was clean and sweet, whereas water from the steam boiler was wayyy more bitter and muddled. Just to be sure I also tested tap water that I boiled before bringing it to the proper temperature, which I sometimes hear people disapproving of. There was a difference but not large enough for me to conclude anything. You’re absolutely right about the water kettle being a must-have!

  6. Love the Q&A,

    I’m surprised no one has mentioned quickly washing or rinsing their baskets with the tea boiler. Is this also discouraged in light of draining pressure?

    Should we not quickly rinse our oily baskets with a swift purge under the tea boiler?

    I’ve found this effective for decreasing build up on baskets and a quick “clean slate” result for baskets before drying and dosing again.


    • Hi Jesse,
      I haven’t experienced a problem with using the hot-water tap for rinsing portafilters, and can’t see why it would be a problem. The amount of water used to brew tea and coffee is a magnitude greater than that used to rinse.

  7. I worked with steam boilers in nuclear plants. Minerals in the steam in trace amounts can exist; it’s called carry over. Whether there is carryover in steam wands would depend on the design of the machine. Do the machines have a moisture separator that efficiently removes mineral laden water droplets and only allow dry steam to come out of the steam wand? This I do not no. If there was carryover, there would be a pretty low concentration in the steam. This would have little impact on the concentrating effect of steam boilers.

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