You’ll often hear that water is crucial because it’s the main ingredient of a good cup of coffee.
Actually, that’s an understatement:
Water isn’t just an ingredient – it also acts as a solvent.
This means that water is an essential factor in the extraction itself, and as such, should be treated with the same level of respect as your expensive burr grinder or handcrafted Japanese pour over coffee maker.
I had known about the importance of water for a while. Still, it wasn’t before returning home to Denmark after living abroad for an extended period that it dawned upon me just how important water is.
The same specialty coffee that would taste amazing when brewed with bottled water in a different part of the world would suddenly taste dull and lifeless with regular Danish tap water.
I had – without even realizing it – become accustomed to coffees brewed with quality water.
This all happened back in 2017.
What ensued then was a several-year-long quest to understand water and its impact on coffee. Much of this time in deep frustration. Read this post if you want to avoid a lot of the worst headaches.
⚠️ Please note, I have added some new sections to this article, so if you just want to read my updated thoughts, then click here to go the 2021 section.
- Filter coffee: Aim for water between 30-100 TDS. Find a solution that is convenient and consistent.
Don’t go out of your way to find the right ratio of hardness to alkalinity. A low TDS will often be enough to brew tasty coffee.
Use one of the following solutions:- RO Water + bypass tap water
- RO Water + Minerals concentrates
- Soft tap water filtered through a filter pitcher
- Bottled water with a low TDS
- Peak Water Filter (Check out my review here)
- Espresso: Machine health is an important consideration when it comes espresso. If you can access reverse osmosis water, you can make “rpavlis” water with a concentrate of potassium bicarbonate.
Otherwise, go for soft water (i.e. under 80 TDS)
The coffee-water bible
Coffee and water is a surprisingly new topic among coffee lovers.
Water is 98,5% of the content of regular coffee and around 90 % of espresso, so obviously, it has a huge impact.
It wasn’t until multiple British barista champion Maxwell Colonna-Dashwood and American chemist Christopher Hendon decided to join forces to solve the water mystery with their 2015 book “Water for Coffee” that something more thorough was published.
The authors researched the different minerals and salt properties and identified two as having supreme extraction properties: magnesium and calcium.
They also found out that the total amount of mineral content in the water is less relevant up to a certain degree. What’s important is the ratio between total hardness and carbonate hardness (also known as alkalinity).
Total hardness is the combined measurement of calcium and magnesium, while alkalinity is the water’s buffering capacity. The research concluded that a 2:1 relationship is optimal for brewing balanced and flavorful coffee.
It’s tough to find a copy of ‘Water for Coffee’ – the book published by Colonna-Dashwood and Hendon, but it’s worth checking out if you’re able to grasp chemistry and complicated science.
What about TDS?
Until the book came out, it was widely believed that ‘total dissolved solids (TDS) was a valuable way to measure and talk about water for coffee. But in fact, TDS is a broad term that includes more or less everything in the water.
According to the two authors, it’s a lot more essential to focus on the relationship between hardness and buffer and the type of minerals.
I think they are right in theory. But in practice, it’s straightforward and easy to use a TDS-meter. It’s much more complicated to measure the ratio between hardness and alkalinity.
What to do with this knowledge?
Tap water in most parts of the world just isn’t suited for coffee brewing.
Even if it’s clean and potable, it can still be very high in calcium and bicarbonates. And oftentimes, there will be nasty tasting compounds as well.
That leaves you with a few other options:
1: water filter pitcher
A water filter pitcher can be a decent solution if your tap water is not too hard. If your tap water is less than 200 TDS, you’ll be able to get it down to an acceptable level.
You can even filter your water twice. It sounds a bit lo-tech but works well.
If you live somewhere with very hard water, a filter pitcher will not help you. Or at least it will be costly in cartridges, making the next solution more affordable in comparison.
2: Bottled water
Bottled water is a decent solution for home baristas. Volvic is quite popular among home baristas in the US, while ‘Ashbeck’ from Tesco is the UK’s water of choice.
I would encourage you to try a lot of different brands and trust your taste buds.
Usually, the cheaper water in nondescript bottles is better. Sometimes this is referred to just as “purified drinking water”.
Most of the expensive natural spring waters – like San Pellegrino or Evian – are jampacked with minerals, and for that reason, they are not suitable for coffee brewing.
3: Use a pre-made formula
Adding a mineral mix to RO Water has become very popular in the last couple of years.
Third Wave Water is the most famous and widely available one. You open the sachet and add it to a gallon of RO water. Usually, I will only use half of the sachet’s content to dial back the intensity of the brew a bit.
Other brands are available, such as Aquacade, which claims that their mineral mix is sourced “naturally” from deep-sea waters.
I like this solution because it’s both easy and consistent. If you quickly find RO Water or something called “purified drinking water” with a very low TDS locally, then I’d encourage you to give this solution a try.
4: Bypass water
Another option, which a lot of coffee shops use, is to “bypass” water.
Essentially, this means that you have a primary water source that is completely stripped of minerals. This is typically RO Water. Then you add some tap water to add a little bit of hardness and alkalinity to get a more natural taste. If you live somewhere with hard water, you might only have to bypass 10% tap water.
The Coffee Collective in Denmark is doing this, and they aim to land on a total TDS of 30, which is very soft.
5: WATER RECIPES
Many home-baristas have begun creating their mineral blend.
First of all, you need a blank canvas to experiment with – some extremely pure water. Realistically that means a TDS around 1-10.
In some countries, it’s easy to find reverse osmosis water (aka RO water), which is very clean.
In other places, such as Scandinavia, it can be a lot harder to find.
Some common ingredients, such as Epsom salt (magnesium) and baking soda (bicarbonate) – can be bought in most supermarkets or health food stores.
Some recipes also use calcium for the hardness. Calcium improves mouthfeel, and in my opinion, it’s more ‘natural’ tasting than magnesium.
Buying all the necessary minerals won’t set you back more than 15 dollars, and you’ll be able to create hundreds of gallons of water.
To create custom water, it’s a good idea to buy a cheap TDS-meter from a place like Amazon (I’d recommend this model).
Mineral concentrates
- Espresso water: I recommend using the basic recipe for “rpavlis” water: Add 1g potassium bicarbonate to 100 ml of RO water for concentrate.
- Add 10 g of concentrate per liter of brew water.
- Use only 5 g of concentrate if brewing darker roasts.
- Filter coffee: Currently, I prefer to use a two-part formula without magnesium.
- Add 5 g calcium chloride dihydrate to 0,5 liter of water. This is your concentrate. Add 10 grams of the concentrate to 1 liter of water. This will get you 67 ppm of calcium.
- In a different bottle add 1,5 g of baking soda and 1,5 grams of potassium bicarbonate to 0,5 liter of water. Add 10 grams of this concentrate to 1 liter of water. This will get you 33 ppm of alkalinity.
- Add the calcium to your brew water first, then the bicarbonate solution.
- Obviously, you can scale the mineral content up and down. If you only add 5 grams of each concentrate, you will have half the mineral content, ie; 33.5 ppm calcium and 16.5 ppm alkalinity.
I have experimented with this recently and seen promising results by not fully boiling the water.
2021 update
Since I wrote this article about coffee water several years ago, I have come to a few new conclusions.
You can still read the rest of the article because it provides some context to the whole debate, but in the following, I’ll summarize my current 2021 “stance,” so to speak.
Flavor first
Maxim number 1: Flavor is more important than theory
When water first became a topic of interest in the world of coffee, much of the discourse revolved around the book “Water for Coffee” and a series of blog posts from Barista Hustle.
The science-heavy book inferred a few “Golden Rules” when it comes to coffee water. Here are some key takeaways from the book:
- A hardness-to-alkalinity ratio of 2:1 is ideal.
- Magnesium and calcium are the most important minerals for coffee extraction.
- Magnesium is more desirable than calcium since it doesn’t cause limescale.
Barista Hustle took these concepts and created a range of water recipes based on the ideas. These recipes mostly relied on combining various concentrates of baking soda and Epsom salt.
However, after much experimentation, I have concluded that I don’t like the flavors that this type of water formulation produces.
A significant amount of magnesium tastes slightly artificial to me. Even with calcium as a secondary source of hardness, I can only tolerate small amounts of magnesium.
Also, high-TDS water recipes often taste too overpowering for my palate. Overall, I prefer water with a lower TDS in the 40-80 range. There can be some exceptions to this, however. With some very light Scandinavian roasts, it can be necessary with a “hardness” boost to extract the best flavors, but this is rare.
By now, I also know of several famous coffee shops and roasters who have given up on the magnesium and 2:1 paradigm.
Instead, they opt for a very soft water with a more natural composition. This is achieved by mixing RO Water with tap water to reach a target TDS, typically in the 30-60 range.
There’s also a fascinating study by Royal Coffee (perhaps one the best coffee importers in the industry) where different minerals and formulations are blind-tasted by their team of professional cuppers. The result is that calcium is favored over magnesium and that distilled water is ahead compared to unique formulations such as Global Customized and Third Wave Water.
Consistency
Maxim number 2: Water shouldn’t be a variable
The second heuristic is that consistently “good” is better than sometimes “perfect.”
When you begin mixing your own mineral compositions, minor errors can make a significant difference.
I know that trying different minerals and compositions can go from a small experiment to a never-ending process from personal experience. The main problem with that is that you will focus more on the water than the coffee.
I think water should be consistent. Then you can focus on changing variables in your brewing instead.
Individual solutions
Maxim number 3: It should be convenient
There is no reason to drink the periodic table. Coffee water doesn’t have to be perfect.
As long as it’s not masking the inherent flavor, your goal is achieved.
Of course, that’s easier said than done since so much tap water is terrible for coffee brewing.
How should you achieve this water? That depends on where you’re living.
In some parts of the world, soft water is available at a low cost.
Elsewhere, you might be able to use a water filter pitcher that can clean up and “soften” tap water to a pretty decent level.
Maybe you can get jugs of distilled water. If that’s the case, it also works well to add some Third Wave Water concentrate.
Find a solution that’s easy AND consistent, and you’ll be able to enjoy your coffee routine a lot more.
Conclusions
My current thinking about coffee water is that it just has to be decent enough.
Sometimes perfect is the enemy of good enough. Creating water that has the ideal 2:1 hardness-alkalinity ratio can be pretty complicated.
I think that the best ROI is to go for water that is good enough. For me, that is, in most instances, water between 30-100 TDS.
Some coffee people claim that TDS is not a good measurement alone, and in a sense, they are right. All the dissolved solids could, in theory, be table salt. However, in practice, it’s almost always a pretty balanced mix of salts and minerals.
Some coffees will be more suited to waters at 30 TDS, and others will work well with water that is slightly outside the range.
Making mineral compositions have often resulted in disappointment. When I experimented with this, I have had the best results when using water with most or all of the hardness coming from calcium. Luckily, this is the usual composition of naturally occurring water.
Don’t boil it
The last tip about water I got recently from the Irish coffee guru and barista champion Colin Harmon. In his book “What I know about running coffee shops,” he explains that you can actually boil the oxygen out of the water and consequently make it less efficient for brewing.
“Water is deoxygenated by boiling, and that makes it quite flat and dull for coffee brewing. Using fresh water and knocking your kettle off just before it boils will ensure the water is at its best,” he explains.
“A simple test you can do at home is to boil a kettle and then leave it a few hours to cool down. Once it’s back to room temperature, re-boil it and make a cup of tea or coffee. Then, very quickly, dump the water from the kettle, replace it with fresh water, boil again and make another cup of tea/coffee for comparative tasting. You should now have two cups, one made with fresh water and another made with re-boiled water, and the results should be quite stark. The freshwater will have more vibrancy, better flavour and should generally be a lot more delicious. The previously boiled water brew by comparison will be flat, dull and lacking flavour.”
over to you
Being a coffee geek, people always ask me about recommendations for the best burr grinders, new gadgets, and so on.
Now I usually tell them to get some good water first and then worry about the rest after. It makes that much of a difference.
Cheers in perfectly extracted coffee!
* Image: Steven Depolo | Flickr | CC
FAQ
A lot of people just use tap water when brewing coffee in their home. Depending on where you live and your municipal water supply that can be perfectly healthy. However, when it comes to flavor, it’s rarely the best option.
You can use spring water for coffee. However, you definitely want to check that the mineral content of the water isn’t too high. Many brands of spring water are actually way too hard. Usually, it’s better to use cheaper bottled water – the stuff that’s labeled ‘purified water’.
Some people claim that alkaline water is ideal for coffee. It’s definitely better than it’s opposite; acidic water. However, a soft water with a neutral pH around 7 is usually ideal.
Thanks for a very great and easy read. I think it means a lot that reading about coffee water chemistry it doesn’t become too complicated – which is quickly could. I’ve been looking quite a lot into good water for coffee as well but mostly by doing a quite extensive research on bottled water. Have been to quite a lot of supermarket to find the right water. This has resulted in quite a huge photo library of bottled water (geek alert!). So far I agree with you that Volvic in i.e. the UK is doing quite well. In Denmark my preferred bottled water is Aqua d’or, which has a bicarbonate of 120ppm, magnesium of 3mg/l and calcium is 36mg/l. There are better waters in DK but this one is most convenient.
And especially convenience is what I think is the biggest problem when it comes to coffee water. Because where do you buy RO Water? I’ve looked everywhere it’s impossible to buy – unless you wanna buy in a huge bulk and don’t care about the price. It a real struggle that suddenly makes mixing the ingredients seem quite easy – whereas acquiring the water to begin with is where the problem lies. What do you think and do you have any experiences with this?
Best
Michael // @mic_schmidt
Hi Michael, thanks for the kind words! I’m a bit of chemistry n00b so that’s why I prefer not to go too much into the details 😉 I agree that convenience is an important part of the equation. The water doesn’t have to be perfect, it just has to be a lot better than (Danish) tap water. In many countries where the tap water is low quality, RO water can be bought everywhere. In Denmark where the tap water is actually not unhealthy I think an aquatic store is the best bet for RO. The Aqua d’or seems like it could benefit from a few sprinkles of Epsom salt 😉 Good luck, and please report back if you find something awesome!
This was a great guide and article.
I really enjoyed it and it explains a lot.
Great info graphics too.
/Michel
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Thanks you so much, Michel! Feedback like that is what keeps me going 🙂