It's an often-quoted fact that 98 percent of a cup of coffee is water, so it stands to reason that water has a big impact on the flavour of coffee. In the case of espresso machines, using the wrong water can also damage them, so water is an important topic. However, it’s also a topic which has the potential to be very complicated on both a theoretical and a practical level. In this article I will try and be as succinct and practical as possible. I want to encourage those who have not yet experimented with the impact water can have on coffee to take the plunge and start experimenting. For those interested in the delving deeper into the science, I have listed some recommended reading at the end of this article.
What is good coffee water?
Good coffee water is not the same as good drinking water. However, while water that tastes delicious drunk as pure water might not bring out the best in a particular coffee, water that tastes actually bad will surely not be good water for brewing delicious coffee. Here I am thinking of two cases in particular: tap water which has a strong taste and odour of chlorine, and bottled mineral or bottled distilled water which may taste of plastic. Use your senses to make the call here: If water smells and tastes bad, I would not use it to brew coffee. This is also the case for the brew water coming out of the grouphead of your espresso machine, which I recommend tasting from time to time.
The distilled water readily available in some countries is not intended for consumption and is often labelled explicitly as not fit for consumption. Whether or not you decide to consume it is – of course – up to you as an individual. I have tried lots of distilled waters, including a fair number which were specifically labelled as unsuitable for consumption and many of them did not taste good. The waters often tasted 'dead' or 'flat' and many also had a strong plastic odour and taste. Whether this can be perceived in the brewed coffee is one consideration, but another concern I have is the potential health impact of consuming this water long-term and on a very regular basis. These may also be concerns with mineral water sold in plastic bottles although in my personal, and anecdotal, experience I have only rarely picked up such strong plastic notes with bottled mineral waters. It’s worth noting that the Speciality Coffee Association (SCA) stipulates (among other things discussed below) that water should be clean and fresh and odour free.
Two important parameters for good coffee water
If you do some internet research on the topic of coffee water, you will likely come across the acronym TDS. TDS stands for total dissolved solids or in other words the total amount of all dissolved minerals in the water. This includes total hardness and total alkalinty. The Specialty Coffee Association recommends a TDS of 50-175ppm (parts per million) The TDS of water can be measured very cheaply and simply with a TDS meter and these can be purchased very cheaply. What you'll probably read less about is total alkalinity. This is something that the TDS meter unfortunately cannot reveal. In his book The Physics of Filter Coffee, Jonathan Gagné says that “total alkalinity is probably the most important parameter which affects the taste of our coffee, apart from contaminants that could impart a bad taste to the water itself.” The target alkalinity defined by the SCA is 40ppm and the acceptable range is defined as 40-70ppm. An even lower alkalinity than this might be desirable and worth experimenting with if one likes high perceived acidity in their coffee. The interplay here with water, coffee and roast level is interesting and complex. For example, if the taster’s preference is for light and bright coffee, then they might 'push' a darker roasted coffee a little in this direction by brewing with lower alkalinity water thus increasing the perceived acidity in the brew. Phew. Did I mention that coffee is curious?
micsmox’s maxim: taste trumps theory
It's easy to get bogged down in the science of coffee water and confused by conflicting information about the ideal water for coffee and as a result end up trying nothing at all for fear of not getting it just right. Water is undoubtedly an important piece of the jigsaw, but your water doesn’t have to be perfect for you to make great coffee. You can still make very tasty coffee with water that isn't absolutely perfect. As with many things the difference between bad and good is much greater than between good and very good. When I experiment with new water recipes (like my Lotus Coffee Products water recipe – Bright and Juicy) I often cup variations of a recipe blind and include a cup made with tap water. This cup stands out as immediately flat and lacking in acidity. The other cups on the table will be much closer and perhaps even indiscernable.
I would encourage you to experiment. Comparative tasting is THE BEST way to improve your sensory skills.
Experiment Choose three bottled waters and do a cupping (I will upload an introduction to cupping on my blog soon) with these waters and your tap water. If your tap water is horrible for coffee like mine is here in Michigan - all the better! I suggest setting up a blind cupping ideally with a friend or group of friends. Alternatively, you can set up a blind cupping on your own. In a second step you could go on to compare the two winning waters, for example, in a 'brew off'. Here I would recommend using a method which you know well to brew the coffees. Immersion brewing methods like aeropress or the clever dripper work particularly well, as they remove a lot of the human variables from your brew. |
So what water options do we have?
Assuming the reader is in the unfortunate position that their tap water is not suitable for brewing coffee, then there are various options available:
Filters
Jug filters of various makes are available. Most jug filters remove some impurities from the water such as chlorine and heavy metals and some reduce the total hardness of the water. If your tap water is generally good (for coffee) but just a little hard, these might be a good option. Just be aware that the effectiveness of these filters declines as the filter cartridge ages. One particulary interesting option is the Zerowater filter which reduces the hardness and the alkalinity of the water to a very low level. The water from this filter can then be re-mineralized or mixed with tap water. Two good options for remineralizing are discussed below.
Bottled water
Bottled water can be good for brewing coffee. It is not possible for me to recommend one particular bottled water for this purpose as this will depend on where you live. But for brewing filter coffee I would suggest searching the local online coffee forums to see what people suggest or asking coffee friends.
Adding minerals to de-ionized or distilled water
You can buy large containers of distilled water suitable for consumption and add minerals to make your own coffee water. I would urge you to try a sip of your base water before and your coffee water after adding minerals and before you use it to brew coffee. I am in the fortunate position to be able to buy fresh de-ionized water from my local supermarket and this tastes much fresher and more ‘alive’ than distilled water in bottles. You can take your own large containers (glass or BPA free plastic would be my recommendation) and fill them up in the supermarket. This works out very cheaply and I also imagine is more ecologically friendly than buying water in disposable plastic bottles.
You can mix your own minerals into water to create great coffee water. This is cost effective but no easy matter and unless you are very keen to dive deep into this particular rabbit hole, I recommend checking out the coffee water products on the market. There are some very good and affordable options. Two which I use regularly and can recommend to the home brewer are Third Wave Water sachets and Lotus Brew Water Sets. If you just want good and reliable coffee water, then the Third Wave or a similar product would be a good choice. You simply mix the powder in one sachet with the suggested amount of water (distilled or reverse osmosis) and you have some great water for brewing your coffee. Third Wave Water offer different variations, including one especially for espresso machines. Some people find that when brewing lighter roasted coffees, they prefer the results with Third Wave Water by diluting the sachets with more water than is recommended. If you want to be able to really experiment with different water profiles and the impact these have on your coffee, then the Lotus Water drops are a great option. You can look up different recipes on their website and once you have tried these you can experiment with your own recipes. I was honoured to be asked to contribute a water recipe myself which is intended to work well with lighter roasted washed coffees. You can find the recipe here
One other option – perhaps more for the extroverts amongst us – is to ask at your favourite cafe if they would be so kind as to fill up a container with their water from the reverse osmosis system. I've tried this at a couple of places with mixed results. I'd consider combining it with buying some of their beans and not asking during rush hour!
So now you’ve finished reading, it’s time to take those first steps and get experimenting!
Happy brewing!
Further reading
For a very detailed and at points rather technical discussion of coffee water along with practical information on mixing your own water I recommend Jonathan Gangé's The Physics of Filter Coffee (2021).
For a very deep look at the topic of water for coffee I recommend the book Water for Coffee by Colonna-Dashwood and Hendon (2015) Unfortunately this book is out of print and hard to come by. I have heard rumours of a new edition though so fingers crossed. In the meantime you can find a talk by Maxwell Colonna-Dashwood online titled water chemistry and its impact on coffee flavour.
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