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The Relationship Between Coffee And Water

water droplet

Not all water is created equal

You might be reading this blog post and thinking to yourself, "surely water is just water." Well, we are here to tell you that you this is not the case, and the relationship between water and coffee is far more complex than most people realise. Considering that water typically comprises of more than 98% of filter coffee and 88-92% of espresso coffee, it is not surprising that the impact it has can be huge. Luckily for us, coffee can be fairly consistent and likes to play by the rules, so to begin, let's look at a few truths that apply to the relationship between water and coffee. 

  1. If your water is inconsistent, your brews will also be inconsistent.
  2. If your water is bad, your brews will be bad, consistently.
  3. Good quality water can drastically improve your brews.
  4. Having one less variable in your brews allows you to more accurately tweak your recipes.

With these points in mind, let's look at what factors we need to be considering in our water in order for it to be optimised for brewing coffee.


Almost all water contains a plethora of minerals. The amount of minerals in your water is referred to as its hardness or softness; the more minerals you have in your water, the harder it is and vice versa. This is measured as the total dissolved solids or TDS; the TDS of your water tells you what percentage of your water is dissolved compounds. Minerals in your water affect your coffee's flavour in two very distinct ways: minerals have their own unique flavour characteristics and minerals have a significant impact on your ability to extract coffee from the coffee grounds.

pouring kettle filter coffee

The taste of water

Let's start off with the obvious - we've all had tap water that tastes like chlorine, and it goes without saying that we don't want coffee that tastes like a swimming pool. The most common undesirable minerals found in water are chlorine and fluoride. Their largely unpleasant, chemical flavours are often strong enough to carry through the brew and can leave lingering unpleasant flavours. High quantities of metals such as iron can also result overpowering metallic flavours in your brew.

Not all minerals in water are bad though, and no minerals (distilled water) is worse (we'll get to that in the next section). Generally speaking, magnesium and calcium will improve the taste of your water and give it more texture. When applied to coffee, these two compounds will offer distinct differences in the body of your coffee, with calcium highlighting creamier, more textured body and magnesium highlighting a brew's vibrant and acidic characteristics. Of all the minerals found in water, magnesium is definitely the one that has the most notable positive impact.

Minerals such as salt can also act as flavour enhancers, activating certain taste receptors on the palate and making the flavour experience seem more full and nuanced. It might even bring new flavours forward. Having said this, these can quickly become overpowering and only the smallest amounts are desirable.

Water's effect on extraction

Minerals in water are also essential if you want to achieve good extraction of your coffee. To put it simply, the delicious compounds in coffee need something to bond to in order to be drawn out of the coffee grounds and into your drink. Water that is too soft or distilled water will result in low levels of extraction and coffee that lacks body and character.

Having said that, more definitely doesn't always equate to better. Water for coffee is a delicate balancing act. Although the right minerals have a positive impact on brewing, flavour and extraction there is a finite limit to the amount of soluble material that can be dissolved in water - ergo, if the water is too saturated with mineral ions, there will not be enough "room" for flavour compounds from the coffee to dissolve.

Water & your equipment

Espresso Machine

Limescale can be a massive issue when it comes to maintaining your coffee equipment. Limescale is a build-up of minerals inside your equipment that can have a huge impact on how well it works as well as its longevity. Limescale can build up on your heating elements, causing your machinery to become significantly less efficient, or inside your pipes, causing inconsistencies and even blockages.

This is where the double-edged sword of calcium comes into play. Calcium can be a wonderful compound for flavour, as it adds a distinct richness and texture to your coffee, however, calcium is the number one culprit in limescale buildup in automatic coffee machines. Although calcium is potentially desirable in manual brewing, it is something that you ideally want to avoid in your machines. It seems that all water is not created equal and how you're brewing can have an impact on what water you want to use.

Regardless of whether you are using hard or soft water in your coffee machines, limescale is something to be consistently aware of; even soft water will begin to cause issues over time. 

What is the solution (pun intended)

If you want the perfect water for coffee, there are a few options. Some take a little more work than others; it largely depends how much detail you're willing to go into and the amount of control you want to take.

Pourover droplets


If you fancy yourself a scientist, you can create your own water for coffee. You can experiment with adding various minerals, adjusting the TDS, tweaking the PH and creating the perfect water for your everyday brew. This option is no doubt for the extreme coffee nerd.

If this is something that interests you, the SCA has published guidelines on water for coffee, and this would be a great place to start. Check out the SCA's guidelines here.

Ion exchange filters

Ion exchange filters offer a fantastic everyday solution to improving the quality and consistency of your everyday drinking water. These filters remove unwanted chemicals and use an ion exchange to exchange minerals you don't want with minerals you do want. Essentially, the TDS of your water will remain mostly unchanged, but the compounds in the water will be far more suited to brewing tasty coffee.

We're particularly impressed by the BWT Penguin Water Filter. When stacked up against water designed specifically for specialty coffee on a cupping table, we actually found the BWT filter to offer the best tasting brew with several coffees.

Bottled water

Although we couldn't recommend this as a daily use case (the waste associated is astronomical), as a once off when you're out and about or on holiday, the right bottled water is a simple and accessible solution that will offer a great improvement on tap water.

It's all about the variables

Even though it might seem like an inconsequential thing, the impact of water on coffee will surprise you; everyone at CCB was quite taken aback by how much of a difference changing the water made in our HQ experiments. At the end of the day, brewing great coffee is all about managing variables; the realisation that water is not a constant (but with a little bit of work it can be) is a great step towards brewing better coffee every day. 

Leave your thoughts in the comments below. We'd love to hear about your experiments and experiences with water for coffee!


Of the bottled waters readily available in South Africa, which one would you recommend for coffee brewing?

Posted by Richard on November 02, 2020

Hey Richard,

Unfortunately, we’ve not done extensive testing on the local bottled water – most of our testing has been through mineral water made using ion exchanges to remove unpleasant minerals and replace them with desirable ones (check out some of our BWT products, they really impressed us).

Having said that, there are a few bottled waters that are globally recognised as really good for brewing coffee, and the most readily available in South Africa one from that list would probably be Evian.


Posted by Cape Coffee Beans on November 02, 2020

Your statement “The most common undesirable minerals found in water are chlorine and fluoride.” is completely incorrect. First, chlorine is necessary to purify, and second, fluoride is in most parts of the country present in negligible amounts. The problem is excess: too much chlorine makes the water taste awful; too much fluoride doesn’t affect the taste but can affect the teeth, and this does happen in some parts of the country. Enamel is made stronger and more resistant to decay if the right amount of (tasteless) fluoride is present. Too much merely affects the appearance. There are no other side effects though there are anti-fluoridationists who use pseudo-science to prevent authorities putting fluoride in our water. This means more unnecessary decay for all children and the elderly.

Posted by Chris on September 08, 2022

Good day,
Thank you for the article. Will my five filter RO water purification system do away with all the nasty minerals?

Posted by Ernest on September 08, 2022

Ernest – thank you for your question – your RO system will do away with the problematic minerals but it may also do away with the good ones required for extraction. You should make sure that the water is sufficiently remineralised. If it’s a 5-stage system, some of those stages may reintroduce minerals.

Chris – thank you for your comment – We hear what you’re saying but this article is only commenting on water specifically in the context of coffee. Chlorine and fluoride may well be desirable from a general health perspective (we’re not the right people to comment on that) but from a coffee brewing perspective, they’re not desirable. We’re not commenting on what the municipality should use to treat water, but rather what should remain in the water when you make coffee with it. What’s nice about a separate water filter system is you can keep the chlorine and fluoride in your drinking water, but filter it out of your coffee water. Having said that, by the time you consume the water, the chlorine has hopefully already done its job!

Posted by CCB on September 08, 2022

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