Water Effect on Espresso/Coffee Brewing

In brewing the finest cup of coffee, we always talk about the latest grinder for ultra uniform grind size, the most sophisticated brewers out there,the best coffee origin(no doubt important). However, we often take one very important thing in coffee for granted - the water quality.

Why water is important?
Water is the most important and abundant ingredient, in making up to 99% of a cup of coffee. So if the water used is off-flavor, it will be carried into the cup. So it's always recommended to used clean filtered water for your all coffee brewing, you don't want the muddy taste or extra particulate in your morning joe.

Solvent and solute characteristic
There is another important role of water which is as an acting solvent. In the coffee brewing process, it's all about how the water molecules extract the desirable aromatic compounds into the final solution (not the most scientifically precise description but that's the gist). This is why the composition of water (trace elements like mineral etc) is so important. If the water is too pure (distilled water for example), its affinity for pulling the solute will be very high, including those undesired ones. On the other hand, if there're way too much mineral or impurities, the water molecules will be too occupied to dissolve the desired coffee solutes. So the end result would be subpar too.

pH
The pH of the water will also skew the extraction preferential of the water, just like how pH affects a chemical reaction in a chemistry lab. You can imagine it to be more H+ in acidic water and more OH- in alkaline water. H+ and OH- each will attract different characteristic of molecules, which affects the final result.

Scale formation
Last but not least, for espresso machines maintenance, we will always hear about limescale built-up, or descaling. This is yet another role played by water. Water with a lot of minerals (Calcium and Magnesium) are called hard water. When hard water are boiled or heated, the excess calcium/magnesium will precipitate, forming insoluble white solids - AKA limescale. If this happens in an espresso machine, it will clog up the machine and lead to potentially costly repair. To prevent this, descaling (using acids) is done intervally, or the water is softened before going into the machine. Fortunately for us in Malaysia, the water here are soft water and scaling doesn't happen unless you use mineral water from the store.

My experience
Even though our water is soft water, is it suitable for coffee? In my experience, I don't think entirely so. It is safe for the machine because the water doesn't form scale. And for most of the time, the water is clear looking and free from mud particle. However, when brewing espresso with the water at my house, I can always sense that the espresso has an odd aftertaste. It's very subtle but is noticable to me. I suspect this may be the chlorine or some other ingredient used in the water treatment process. My house water is filtered with active carbon filter (Panasonic) and the filter cartridge is changed according to schedule. I tried searching high and low, on the internet, but couldn't find anyone else that has same experience as mine.

I have tried the RO water in my office too. It filters the water alright, but it has an alkaline cartridge that adds salt(not table salt) into the water. So the espresso brewed using that is very thick-bodied, but the aftertaste is extremely short. Too short for my liking.

So, the solution I've come to, is to use store bought bottled water. It seems to improve my espresso quality and no longer gives the odd aftertaste. The aftertaste is long and decent.

But this solution may not be suitable for everyone. And I suspect this is probably not a problem for most to begin with.

But the point is, if you're planning to use bottled water in your machine, beware of mineral water with high calsium/magnesium content. I find that most mineral water will form scale. If you're using mineral water for long term, scale-formation is certain and you need to descale every few months. If not, your best bet is to used filtered tap water because that is the safest water for the machine. Just a bit of compromise in the taste, but it's probably not very noticable to most...