The Best Water for Coffee - An Introduction
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Water chemistry is the most critical and overlooked factor in coffee brewing quality; mineral content (calcium/magnesium) and alkalinity (bicarbonate) must be balanced to extract optimal flavor, and most home brewers can achieve this through testing, treatment, or custom mineralization.
- Mineral ions (calcium/magnesium) are essential for coffee extraction; too few minerals = poor extraction, too many = over-extraction
- Bicarbonate (water alkalinity) buffers pH; excessive buffer masks acidity making coffee dull, insufficient buffer leaves coffee acidic and unpleasant
- Most common solutions (Brita filters, bottled water, RO) are suboptimal; custom mineralization of distilled water using Epsom salt and baking soda is most precise and cost-effective
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Calcium and magnesium, while both mineral ions, do not do exactly the same job in coffee extraction; having the same quantity of calcium in one water as magnesium in another will produce different tasting cups, with calcium generally being preferable as the primary ion at slightly higher levels and magnesium preferable at lower levels.
“it's tricky because calcium and magnesium while they are both mineral ions well they're a little bit different they don't do the same job exactly and having the same amount of calcium in one water as you have magnesium in another will produce different tasting cups of coffee when you brew with those two waters generally speaking a little bit more calcium is preferable if that's your primary ion a little bit less is preferable if magnesium is your primary ion”
Reverse osmosis produces nearly pure water, which is not ideal for coffee brewing because pure water can become corrosive in machines and lacks the minerals needed for optimal extraction; most home RO units produce water that is too soft for good coffee.
“what you get out of it though is nearly pure water which again isn't actually ideal if you put distilled water into a coffee machine well that's typically bad because it can become quite corrosive and again we know that we need some minerals in order to get the best tasting coffee from an extraction perspective so pure ro is not desirable and there are some home units available and I'll be looking at a couple in the not-too-distant future but in most cases they produce water there's actually too soft”
A TDS (Total Dissolved Solids) meter is not helpful for optimizing water for coffee because it measures only the total conductivity of dissolved solids but does not tell you what those solids actually are—whether calcium, magnesium, or other conductive substances.
“you can very cheaply get a TDS kit but that's not terribly helpful a TDS meter will give you the total dissolved solids for the water but it won't tell you what those solids are could be your calcium could be your magnesium could be all something else that happens to conduct electricity it's not very insightful”
Brita-style water filters do some softening but not much; they improve taste by removing off-flavors like chlorine, but they do not effectively solve the hard water problem and therefore are not a complete solution for optimizing coffee brewing water.
“these things do a little bit of softening but not too much they definitely improve the taste of the water if your water has off tastes like chlorine or other unpleasant flavors but they don't really do a great job softening so I'm not against them but they don't fix the problem”
Using water with chemical problems means you will either fail to extract the coffee flavors you've purchased, or the coffee you do extract will taste much worse.
“using water that has some problems means that you're not going to extract the coffee that you buy or you're gonna make the coffee that you extract taste much worse”
The Specialty Coffee Association (SCA) provides free online guidelines and ranges for water quality specifications that are publicly available and useful as additional reference standards beyond individual recommendations.
“there are specs that are used in international coffee competitions that are available online the sca the Specialty Coffee Association they offer a guideline I kind of range for various things when it comes to water quality that's free and available online so check that out too”
For tap water in many parts of the world, you can enter your postcode or zip code into your water authority's website and obtain an exhaustive breakdown of mineral content for free, which is essential for understanding your water chemistry.
“if it's coming out of your tap well in many parts of the world you can put in your postcode or your zip code into your water authorities website and they will give you an exhaustive breakdown of the minerals inside that water that is definitely useful it's usually free in most parts of the world go and check that out that's essential”
Mineral ions like calcium and magnesium help coffee flavors go into solution during extraction, and having no mineral ions results in very little extraction compared to having abundant ions.
“these are really useful ions if they're in the water they actually help with the extraction of the coffee flavors helping them go into solution to create a delicious cup of coffee if you have no mineral ions you'll have very little extraction compared to having a lot of ions and then having a lot of extraction”
More mineral ions does not necessarily mean better extraction or flavor; there is an optimal range beyond which additional minerals do not improve taste.
“but that doesn't mean that more is necessarily better”
Bicarbonate/alkalinity in water buffers pH by resisting acidification; high alkalinity requires more acid to lower pH, while low alkalinity allows acids in coffee to remain uncontrolled and unpleasant.
“this refers to the ability of that water to sort of buffer its pH to maintain its pH around about 7 if you have a lot of bicarbonate if you have a lot of alkalinity it'll take a lot more acid added to that to turn the solution acidic in the case of coffee while coffee is pretty acidic when you extract a bunch of stuff in coffee those are acids it has a low pH when you brew it so the more buffer that you have the less acidity ultimately you're experiencing your cup of coffee”
Like mineral content, bicarbonate/alkalinity follows a Goldilocks principle: too little leaves coffee acids uncontrolled and unpleasant, too much makes everything taste boring, dull, and brown; there is a middle ground where things taste great.
“to little bicarbonate is a problem those acids in the coffee will run rampant they'll be uncontrolled unbalanced unpleasant too much buffer then everything is just kind of boring dull brown tasting to be avoided with both of these things there's a middle ground where things tend to taste pretty great”
Creating custom mineralized water by adding measured amounts of minerals (magnesium via Epsom salt, bicarbonate via baking soda) to distilled water is possible and allows for precise composition control for optimal coffee brewing.
“you can get a bunch of distilled water and go and buy your individual components for the mineral content you can use magnesium in the form of Epsom salt that's cheap and easier to get hold of and for the bicarbonate you can just use sodium bicarbonate which is baking soda which is incredibly cheap and easy to get hold of and you can very simply put a small amount of those into distilled water and then carefully dilute that down again into a much larger quantity of distilled water to very accurately very carefully compose mineral water”
Brita-style filters contain a filter mesh to remove particulates, active carbon beads (charcoal) that absorb off-flavors like chlorine, and ion-exchange beads that are negatively charged and swap out calcium ions for sodium ions without creating saltiness or health concerns.
“inside at the top here you've got a pretty simple filter mesh that is just like a tiny sieve to remove any particulate matter make sure there's no floaty bits in the water as it goes into the main filtration section and below that there are lots of these little tiny kind of beads and there's there's two types here now I'm pretty confident that the darker ones are active carbon they're essentially kind of charcoal and what they do is mop up off tests any kind of chlorine II flavors will get cleaned up by active carbon the other little beads are essentially ion exchange beads that they're negatively charged and they attract the calcium and in their place release a sodium ion”
There are two primary aspects of water chemistry relevant to coffee brewing: mineral ions (primarily calcium and magnesium) which aid extraction, and bicarbonate/alkalinity which buffers pH.
“there are two aspects to water and it's its contents that are particularly important when it comes to brewing coffee the first are the mineral ions most commonly we're going to talk about calcium and magnesium these are really useful ions if they're in the water they actually help with the extraction of the coffee flavors”
Reverse osmosis filters work by pressing mineralized water against an extremely fine mesh through which only water passes while minerals are blocked and wasted; RO units are incredibly wasteful in their water output ratio.
“you press your your mineralized water against a mesh that is so fine that only water can get through but the minerals can't it's applied with pressure and anything else is who runs off down the side of the filter and out and becomes waste reverse osmosis units are incredibly wasteful”
The difference in coffee quality between brewing with soft water versus hard water is enormous and is not just perceptible to professional tasters or coffee enthusiasts but is detectible by anyone and everyone regardless of expertise.
“go and brew two cups of coffee get a French press brew two cups of coffee one with soft water one with hard it's not difficult to do and it will ruin your day because the difference is enormous and it's not just testable by professional tasters or coffee geeks or obsessives it's anyone everyone can taste the difference between good water and bad”
Barista Hustle (Bristol Hustle) is a major resource that has done extensive work popularizing and systematizing custom water composition, providing calculators for creating mineral recipes and for mineralizing soft water to optimal ranges.
“I just can't talk about this subject without giving an enormous shout out to barista hustle many of you are familiar with Bristol it's Matt Berger's kind of coffee brain trust that puts out enormous amounts of information into the world if you are not aware of it go to Bristol hustle calm right now and stop watching this video and go and learn some really cool stuff they did a ton of work on composing your own water they really popularized this they have calculators to do it yourself to creator and recipes they have calculators for taking very soft water from your tap and mineralizing it a little bit more to get it into a really good zone for coffee brewing”
Hard water causes limescale precipitation when heated in coffee machines, which can easily damage, break, or clog equipment; this is a separate and serious problem beyond just poor coffee taste.
“the problem with hard water is not just that it doesn't make great tasting coffee the problem with hard water is limescale and when I two coffee machines espresso machines filter machines heating that water up causes limescale to precipitate out and that can easily damage break clogged frustrate your coffee machine”
Brita-style ion-exchange filters have finite capacity; they will eventually release all their stored sodium and stop softening, even when brand new, they are not super effective with very hard water.
“it will do an okay job but it is finite alright at some point it will release all of the sodium that it has and so it will not do any more softening and even brand new fresh they're not super super effective with very hard water”
Some bottled mineral waters may have adequate mineral content but inadequate bicarbonate, producing harsh, acidic, and unpleasant tasting coffee; proper balance of minerals and alkalinity is required even with bottled water.
“there are plenty of waters out there that have what seemed like the right mineral content but have inadequate bio-cop they producing with its harsh and acidic in a kind of unpleasant way so to be avoided”
Recommended water composition for coffee brewing is approximately 30-50 parts per million calcium, 15-30 ppm magnesium, and 50-75 ppm bicarbonate, though these are not absolute targets and exist within a spectrum of acceptable ranges.
“if I was talking about calcium I might say 30 to 50 parts calcium is good but if it was magnesium I might say more like 15 to 30 parts per million or milligrams per liter is good similarly with buffer I might say so between 50 75 maybe ppm”
If water has been treated or softened, the best way to assess its composition is with a dropper kit, which are cheap and work by adding drops of reagent until the water changes color, providing total hardness and carbonate hardness measurements that can be converted to mineral and bicarbonate content.
“in case the waters been treated or softened in some way then pretty much the best way to assess it is with a dropper kit they're pretty cheap well I'm sure there are links available and you take a sample of water and you add drops to it until it changes color and those droplets give you an indication of total hardness and carbonate hardness those can be converted so you can find out sort of how much mineral hardness is in there and how much bicarb is in there”
Third Wave Water is a commercial pre-packaged sachet solution that provides convenient custom water mineralization for those who want precise composition without the effort of DIY mineral mixing.
“much as third wave water is a nice little solution that is available just off the shelf if you want to go harder than this you can you can get a bunch of distilled water and go and buy your individual components”
Maxwell Colonna-Dashwood and Christopher Henderson (For Coffee) have done significant work researching and explaining water chemistry in coffee and provide great reading material on the topic.
“and one more shout out has to go to Maxwell Colonna Dashwood and Christopher Henderson with for coffee which really dug into what's doing what and why it gives you a great primer on water chemistry I think it's pretty hard to get hold of at the moment but I'll stick some links in the description down below if you really want to understand this a little bit more I think it is great reading”
If you buy from one roaster continuously, finding out what their water composition is and matching your water to theirs as much as possible or practical will get you much closer to the tasting notes they describe on the bag.
“if you buy from one roaster continuously if you buy their coffee all the time find out what their water is like matching your water to theirs as much as is possible or practical will get you much closer to those tasting notes that they're writing on the bag if you're brewing with water that's a long way away from theirs you'll just have a very different taste experience to them which can be a little bit frustrating”
Even with excellent coffee equipment and excellent brewing technique, poor water quality prevents achieving the 'certain sparkle' and sweetness that specialty coffee shops can achieve with their properly treated water.
“you just use the tap water as it's soft enough or is it hard do you feel frustrated sometimes that the coffee you make simply is not as good as the coffee from the local coffee shop that certain Sparkle that sends sweetness that their coffee has you just can't get no matter how good your gear and how good your technique”
Bottled mineral water is an impractical solution to hard water because it is wasteful, expensive, environmentally unsound, and unsustainable, even though mineral water labels in Europe and elsewhere often provide useful mineral composition information.
“it's one of my least favorites it's inelegant frustrating wasteful environmentally unsound and then of course is bottled water in Europe and many parts of the world it's a kind of requirement in bottled water to put the mineral content on the label often on the back and they'll give you the exact quantity of magnesium and calcium and your bicarbonate and a bunch of other stuff in milligrams per liter which is really useful”
Water chemistry issues can hold people back from extracting the value and quality that is in the bag of beans they purchased, and small changes in water composition can have massive impacts on final cup quality.
“water really is the most frustrating thing it can hold you back from getting out the value and quality that is in the bag of beans that you bought it drives me kind of crazy that it seems so simple but it's so complicated and little changes can have a massive massive impact”
RO water may need remineralization to become suitable for coffee, which adds complexity and cost to home RO systems, making it not a great overall solution if your water is only slightly hard.
“it'll taste fine and it won't be so soft that it's actually corrosive but it won't be their best possible water you may need to find some way to remineralize it which can be complicated so again that's not a great solution if your water is just a little bit hard it's not super hard then something like a Brita is kind of actually okay and not a terrible solution”
Getting treated water from a local cafe or roastery that has optimized their water for coffee is a viable option if the business is willing; while it shouldn't be free (there is a cost to the cafe), negotiating to purchase water is reasonable.
“one option is to get water from a local cafe or a local roastery that treats its water not every business is going to do this for you not every business is going to be interested in that but I hope more and more get on board with the idea of sharing the water that they're making now I don't think I could ask a cafe to give that away for free there is a cost for them in creating good tasting water for coffee so I would expect to pay something not just expect them to give you two three five liters of water free but talk to your local cafe they may be open to this”
Creating custom mineralized water is an extreme solution that requires effort, patience, accuracy, and some expense (cost of distilled water and minerals), but the results are genuinely enjoyable and eliminate concerns about water quality affecting home coffee brewing.
“this is unquestionably extreme as a solution it's a little bit expensive to buy demineralized water it's a little bit of your time and effort to do this stuff it requires accuracy and patience and a willingness to do it but the results are really really interesting and are definitely enjoyable when it comes to making delicious coffee in the morning it's really nice to just not worry about the quality of water that you're brewing with and if you live in a hard water place that's an almost unimaginable thought”
Water chemistry is a known and documented problem in specialty coffee that has been studied for many years, with significant prior work done by coffee experts like Jim Schulman in the early 2000s.
“and again this is not entirely new I remember reading great stuff by Jim Shulman way way way back in the early 2000s he'd done a bunch of work on this stuff too it's been a known problem for a long time”