Everything You Should Know About Water for Coffee

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: Since I originally started working on this article six years ago, I have learned so much new about water for coffee.

I have collected all this in this my course on coffee water – here I break down all the complicated stuff in 26 video lessons and share recipes/techniques and tools with you.

If you don’t want to waste years down the rabbit hole of water chemistry, I’d highly recommend checking it out.

 

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 salts and identified two as having supreme extraction properties: magnesium and calcium.

They also found out that the total amount of “total dissolved solids” in the water is less relevant up to a certain degree. According to the two authors, what’s important is the general hardness (GH) and carbonate hardness (KH – also referred to as alkalinity or buffer).

Total hardness is the combined measurement of calcium and magnesium, while carbonate hardness is the water’s buffering capacity. The research concluded that a 2:1 relationship is optimal for brewing balanced and flavorful coffee.

While there’s not really a consensus on this exact ratio in the coffee world today, most people agree that GH and KH are two essential aspects to understand, when it comes to adjusting the ideal coffee water.

KH is really what determines the acidity of the water. If you have more carbonate hardness, it’s more difficult for the extracted coffee solubles to make the final brew acidic. That’s a double-edged sword, because most of modern coffee’s flavor comes precisely from acidic compounds. So you want to balance it, but you don’t want to mute it.

The minerals that contribute to GH (pretty much just calcium and magnesium) add flavor, mouthfeel and perception of body. According to the authors of Water for Coffee these minerals also increase extraction, but there’s some contention around this today.

The book “Water for Coffee” has been out of print for years, but it still stands as an important turning point for the conversation, which had previously revolved around the more ambiguous term TDS (total dissolved solids).

Where are we today?

While the book offered valuable insights and was revolutionary back in the day, some of its ideas evolved in unexpected ways, particularly leading to an excessive focus on magnesium without considering its broader effects. Adding magnesium to water can be achieved through various methods, but a problematic trend emerged: the widespread use of Epsom salt in brewing water without critical evaluation.

The challenge with Epsom salt (and other salts as well) lies in its composition – while it provides 25% magnesium, it also adds 75% sulfate into the water. This means that you can quickly run into pretty extreme sulfate concentrations.

In theory, it’s easy to obtain a perfect 2:1 ratio between GH & KH. But what if the water has unnaturally high amounts of sulfates and sodium as a result? Shouldn’t that be taken into account. I think it should.

Years ago, after some experimentation, I decided that remineralized water wasn’t really for me. It simply tasted too unnatural, and I could get more consistent results by mixing various water sources.

A litte sidenote here: There is a phenomenon known as the naturalistic fallacy – the mistaken belief that “natural” automatically means “better.”

While I don’t embrace this view, I do believe that outright “artificial” or “chemical” tasting isn’t something to strive for in the realm of coffee.

This isn’t about natural versus artificial in terms of ethics; it’s simply about what tastes good.

It’s only recently that we have to started to see more debate around individual anions and cations and their effect on sensory perception.

Personally, I will say it wasn’t until I fully understood this aspect that I was able to formulate mineral concentrates that fully matched or even exceeded more “natural” tasting water.

What about TDS?

Before “Water for Coffee” was published, the coffee industry relied heavily on TDS (Total Dissolved Solids) as the primary way to measure and discuss water quality for coffee brewing.

Even the Specialty Coffee Association took this simplified approach, recommending water with “TDS around 150 ppm.” But here’s the thing – TDS is just an umbrella measurement that counts pretty much everything dissolved in your water.

This raises an interesting question: if you’ve already got your GH (General Hardness) and KH (Carbonate Hardness) dialed in correctly, should we really care about the other stuff like chlorides, sulfates, and sodium?

The pendulum ended up swinging too far in the opposite direction, with people starting to treat the humble TDS meter like it was completely worthless.

I think the debate is more nuanced than that. While TDS shouldn’t be the star of the show, it would be a mistake to completely dismiss its practical value. Using a TDS meter is straightforward and simple, especially compared to the more complex task of measuring the ratio between hardness and alkalinity.

Saying that a TDS meter is not valuable is a little bit like saying a bathroom scale is useless, because it does not discern between fat and muscle mass.

If you gain 5 kilo the bathroom scale doesn’t tell you what those extra kilos are composed of… but given the circumstances, you probably have an idea.

TDS meters are a bit like that when dealing with a natural water source like tap water. Most places in the world the tap water follows a pretty linear relationship between GH and KH. So if you have a reading of, say, 100 ppm, you can often deduce that you have a relatively low level of alkalinity in the water.

For this reason, I recommend TDS meters to coffee enthusiasts as an entry point into water experimentation. While they don’t tell the complete story, they provide a starting point. They are certainly better, than having no measurement at all.

Any cheap TDS-meter will provice a decent baseline – even the models that come for free with the ZeroWater filter jug. However this model here is a bit better since it measures temperature at the same time and will allow you to toggle between different calibrations. Remember, TDS-meters are highly sensitive to temperature, so it’s important always to do your readings at room temperature.

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’s usually still has a high amount of calcium carbonate (aka CaCO3)

Calcium carbonate actually tastes great in the right amounts. But if you have too much it will neutralize the acidity in coffee, which is a big issue.

Oftentimes, there can be nasty tasting compounds such as trace amounts of iron and chlorine as well.

Unless, you live somewhere with perfect coffee water coming out of the tap (Oslo, Norway is one of those few places) you’ll probably have to use a slightly more complicated method if you want the best possible coffee experience. Here’s an overview.

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. However, Brita filters mainly clean up the water and remove some nasty stuff. It doesn’t do much in terms of changing GH nor KH.

If you have relatively soft water naturally, this might be the final touch you need. But in many cases it won’t be enough.

If you live somewhere with harder water, a filter pitcher such as the ZeroWater model is an affordable and practical solution to obtain 0-TDS water at home. Even though the filter cartridges are a bit expensive, I think it’s a good investment, and I use it for my personal water solution at home currently.

Then you can add minerals or even just some tap water back to the 0 TDS water to get to you desired hardness and alkalinity.

There is also a dedicated coffee filter jug from Peak Water – check out my review here. In theory, it’s a great solution. Peak can target a specific hardness and TDS level with a clever dual filtration system.

Unfortunately, it looks like only a few shops worldwide will continue to carry the filtration units, so I’m a bit conflicted about recommending it in 2024. There have also been reports of poor quality control of the filtration units, and people in hard water areas such as Denmark and UK complain about it having a short lifetime, making it a costly solution.

2: Bottled water

Bottled water is a decent solution for home baristas. And it’s a good way to try coffee from a decent water without doing investing in anything esoteric.

Volvic is quite popular among home baristas in the US, while ‘Ashbeck’ from Tesco is the UK’s water of choice. In most countries, there will be a few different brands that are darlings of the local coffee community.

Usually, the cheaper water in nondescript bottles is better than the expensive mineral waters. Sometimes this is referred to just as “purified drinking water”.

Many 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 have appeared more recently such as Aquacode, Apax Lab, Lotus, Perfect Water and probably some more I forget.

There’s also a new startup from the US called Empirical Water, which takes a different approach from other brands on the market. This brand uses Calcium Carbonate as part of the water profile, which creates a more “natural” taste.

Due to logistics issues, I haven’t tried their product, but I agree with much of their reasoning on a philosophical level. In my opinion, Calcium Carbonate is the most natural-tasting way to add both General Hardness and Carbonate Hardness to coffee water, so building recipes around this compound offers many advantages. The downside is that it can’t be sold in a more compact concentrate form, requiring a larger bottle compared to other brands.

Overall, I have tried most of the solutions on the market and while some of them are pretty good, it’s not that difficult (nor expensive) to make even better concentrates at home.

Of course, one of the things you pay for with the pre-made mineral concentrates is convenience. And it’s true that it can be cumbersome to experiment with different DIY recipes, especially if you’re new to the lingo of water chemistry.

However, that’s one of the reasons why I have created my course, Coffee Water Wizardy, where I have several videos that go over how to emulate various popular water recipes at home.

 4: Bypass water

 Another option, which a lot of coffee shops use, is to mix ultra pure water with “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. To experiment with this, you first need a blank canvas – extremely pure water with a TDS around 1-10 ppm.

In some countries, it’s easy to find reverse osmosis (RO) water, which provides this purity. However, in regions like Scandinavia, sourcing such water can be challenging.

Basic ingredients like Epsom salt (magnesium sulfate) and baking soda (sodium bicarbonate) are readily available in most supermarkets or health food stores.

⚠️ Please note: When you’re buying minerals, it’s important to make sure they are food safe. Minerals also have many industrial applications – so it’s not a given that they are safe for human consumption. Similarly, don’t buy destilled water that’s meant for other purposes, such as steam irons, humidifiers, skincare, electronics cleaning etc. This water is usually stored in plastic bottles of poor quality and will absorb flavors from the plastic.

Many recipes also incorporate calcium for hardness – it improves mouthfeel and, in my experience, tastes more ‘natural’ than magnesium. Natural water generally has more calcium than magnesium in most places around the world, so it’s not weird to have this preference. However, it can be interesting experimenting with the ratio of calcium to magnesium. For instance, Third Wave Water uses both types.

The initial investment to buy minerals is modest: If you invest between $20-40, it’s probably enough to create hundreds of gallons of water.

While mixing your own minerals into brewing water sounds appealing in theory, the results can be disappointing. In my opinion, many online recipes fail to properly balance anions and cations, leading to excessive sulfates (from MgSO4) or chlorides (from CaCl2 or MgCl2).

The beer brewing community pays much more attention to this balance, with brewmasters carefully monitoring chloride-to-sulfate ratios. After extensive testing, I’ve found this balance to be just as crucial as the minerals themselves. For example, in my opinion, calcium sulfate and magnesium sulfate have more in common than calcium sulfate and calcium chloride.

Again, this is something I go into in more detail in my course.

💡 Sidenote: if you want to try the effect of 100% chlorides then use Aquacode for your brew water. If you want to experience sulfates, then try Third Wave Water.

Mineral recipes for Coffee Brewing

Conclusion

Coffee water is the biggest and most tricky rabbit hole in all of coffee. I have spend years trying to figure this stuff out, and finally I’m at a point, where it’s starting to make sense for me.

So depending on where you’re at in your coffee journey I think there are different solutions that might make sense to you.

If you’ve never dealt with water as a variable before, it can be enlightening just switching from tap water to a bottled brand.

If you already know about the difference water can make, then you might get good results with mixing a bottled water with ultra pure, 0-TDS water. By doing this, you’ll adjust both GH and KH at the same time, but you’ll still be able to learn a lot.

Trying to formulate your own coffee water with various minerals can be fun but also frustrating. I would try to get a solid foundation in natural waters before taking that leap. Then you’ll have a much better comparison, so you can make an informed decision and see what you prefer.

High-magnesium formulations and complex mineral ratios dominated specialty coffee discussions around five-six years ago.

However, I think we’re somewhere else today. Experience has shown that these recipes often produce artificial-tasting results. In contrast, simply using purified, soft water (40-80 TDS) typically yields more natural tasting coffee.

In the long run, consistency and practicality are crucial. The best water solution is one you can maintain without hassle. Whether that’s filtered tap water, a mix of RO and tap water, or mineral concentrates depends on your location and resources. The goal isn’t perfect water – it’s water that doesn’t mask coffee’s inherent flavors.

You don’t need to memorize the periodic table to make great coffee.

My current thinking is that there’s no such thing as perfect water for coffee. Instead, water is one component in a complex interplay between roast style, brewing method, and personal preference. Some coffee lovers prioritize body, others seek clarity – both are valid preferences, but achieving each requires different water compositions.

If you’re still not scared away, and still curious about water, then I’d encourage you to check out my brand new water course.

FAQ

* Image: Steven Depolo | Flickr | CC