Special thanks to our chemistry guru guest author, Jeremy Hartley.

It shouldn’t surprise me how much water quality can affect a coffee brew, but it still does. More than a year ago, we published our first blog reviewing the findings of Maxwell Colonna-Dashwood and Chris Hendon; we also contributed some extra data of our own. By the end of that time, we knew definitively that not only the overall TDS, but the actual types of ions in your brew water can completely change both the solids extraction and palate of a brew. It was a fun project to be involved with because of the amount of feedback it generated from diligent baristas and readers around the globe.

So it should have been familiar ground to me when we recently recapped with a live presentation and tasting. By the end of the night, I had tasted eight different coffees and if you had told me they were different origins, I might have believed you. But they came from the same roast and were brewed precisely the same way, eight times over; the only difference was the water. It gets me every time!

The question of the difference water makes to coffee is one which raises so many possibilities and issues that it can generate a lot of confusion, which is where this article comes in. We will do a quick recap, but the main point of today’s post is to get practical — how can you use this knowledge in your day-to-day coffee lives?

To recap the basic concepts, there are few things you need to know:

It’s got electrolytes

First and foremost, change your thinking. We’re not interested in water because it is an ingredient in coffee, like mixing a cocktail or making a nice instant in that mug you got from a trade show. We are interested in water because it is a solvent and the whole art of brewing involves altering the properties of a solvent to partition desirable compounds into the liquid phase whilst leaving unpleasant compounds in the solid phase. You already do this by altering the temperature of the water (which changes the solvent strength), but you can also change the nature of a solvent by adding modifiers — in this case, dissolved salts.

There are a few different players in the field of brewing water modifiers, but in a nutshell, there are probably measureable amounts of calcium, magnesium and bicarbonate ions in your brew water and they all affect the extraction. If they are not naturally present, then you can add them.

But what does it all mean for our methods?

You are here

The first thing to say is this; you can’t really use this knowledge to predict effects on the brew. The chemistry is too complex to make reliable predictions such as the following; “If I add more magnesium to the brew water, my coffee will be fruitier and more delicious.” The win is more like, “If I add magnesium to the brew water, something will change, and it’ll be fun and interesting.”

The second thing is this — there may not be a direct win for you in altering your water quality. It’s not always an easy thing to do, but perhaps you can compensate for it with other brew parameters. In a way, you already are and that’s why you need to be aware of this.

You see, through the cupping and QC process, your roaster is unintentionally roasting to make delicious coffee with the water in the cupping lab. It’s unavoidable, and probably no big deal, but if you are stuck on a brew recipe which isn’t working out properly, perhaps it’s a useful tool to have in your kit, or at least something to be aware of so you can work around it.

So it’s all about raising awareness! But for once, it doesn’t involve a disease, an addictive habit (well, maybe) or something bad happening to puppy dogs. On a side note, can the world in general please stop raising my awareness about everything, everywhere. I’m already pretty aware of most things, except where my feet are at a given time.

Brewing with Brawndo

The starting point here is to know where your water comes from, and what filtration is already installed. Geographical variations in water quality are massive. Perth relies heavily on groundwater and there are so many electrolytes in it that you might as well brew with Brawndo. In Melbourne, they flush toilets with very soft, low TDS water. Then there are variations on that theme around the country. Desalination of seawater also produces low TDS water and is of increasing importance in Australia, so things are really looking up for coffee brewing in Perth.

It’s unlikely in a café setting though, that you’re using completely untreated water — what exactly does that filtration thing under your bench do anyway?


Most places will use at least a sediment and a carbon filter. The sediment filter simply catches fine particles which might block up your equipment, while the carbon filter has the main role of consuming chlorine.

In Perth, local water quality demands we take things a step further by adding reverse osmosis (RO), which forces water through an incredibly fine membrane to remove most of the total dissolved solids. This is how desalination is achieved.

The main reason for using RO is actually to do with machine longevity. Hard, high TDS water is corrosive and also leads to boiler scale and blockages.

The poor cousin of RO is the water softener. Water softeners contain little beads of ion exchange resins. These beads do exactly what it sounds like — they exchange ions. Still confused? The beads are loaded with a salt (commonly table salt) and as water loaded with calcium and magnesium flows over them, they do a swapsie, which binds up the calcium and magnesium and exchanges them for salt (chemistry is like black magic, you get nothing for free). The overall result is that you have just made your water softer and less prone to boiler scale, but the high TDS is unchanged.


Remineralisation is a thing you do to undo some of the hard work of RO, which is actually too effective. Very low TDS water isn’t actually ideal for either coffee brewing or machine health (just in case you were gloating, Melbourne!) So the water is passed through a bed of rocks as it exits the filter to add a little TDS back in. On a side note, the technical team at Five Senses has done some fantastic work on discovering the best products and replacement cycles for the remineralisation of RO water (most remineralisation systems actually do very little).

Taking control

This should give you some idea of what kind of water is available to you, which gives a starting point for either modifying it or adjusting brew parameters to compensate for your particular water. For plumbed in espresso machines, changing the water isn’t an easy task. You have the options of changing the water source, improving your filtration system to decrease TDS or adding extra remineralisation to boost the TDS. A more extreme option is to actually build a system which doses the water with precise amounts of electrolytes – I have heard of it being done.

For filter brews, of course, it is much easier and there is much fun to be had. Just try different waters (bottled water, tap water, filtered water etc.) and see what works. You will be surprised how much difference it can make. I would go as far as to say that if you are involved in competition brewing, you are crazy to leave this factor out of your preparation. If you want to go further and craft a specific brewing solvent, you will find instructions and some extra reading in our previous article, Experimenting with the effect of water quality on coffee.

Sit back and watch

I’m personally interested in seeing where the industry’s newfound knowledge of water quality issues leads over the next few years. Maybe one day it will be the norm amongst specialty coffee providers to brew with a much more deliberate composition and we will have an expanded vocab for communicating this? Or maybe we will nerd out about it, but the commercial application will be limited? I’m OK with either, but for now I have a filter brewer and a new parameter to play with.

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