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.
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.
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 from Brita or similar brands 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 low-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.
A better solution could be the dedicated coffee filter jug from Peak Water — check out my review here. Unfortunately, it also has a few downsides and is more expensive.
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 Aquacode, 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 extremely soft.
5: WATER RECIPES
Many home baristas have begun creating their own mineral blends.
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).
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.”
* Image: Steven Depolo | Flickr | CC
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 its opposite; acidic water. However, soft water with a neutral pH of around 7 is usually ideal.