When talking about water quality and coffee flavour profile, many interesting questions come around. Such as, What is a definition of a good water? What exactly is the flavour of a certain coffee if there in fact the water is always different? How do hardness of water affect the brew quality?
Last time, when I was visiting a friend and one of the world best coffee growers Mr. Afonso Lacerda, a young barista Leonardo Gonçalves passed by in search for a good water. After a short conversation about each one position in the coffee world and a cup of excellent cup of one of the best bBrazilian coffees, Afonso showed him a natural spring with the purest water coming from the mountains of Caparaó park. The barista thanked from the heart and after tasting it, filled the bottle and went to prepare himself for the contest. He wanted a perfect water as he was competing on the Brazilian contest in Aeropress that was held in Cafeteria on Sitio Santa Rita few kilometres away.
Some might find his behaviour strange, but the fact is, that 98% of your cup of coffee is water. Subsequently, the quality of your preferred beverage is directly linked to the water used to brew it. And even though someone might think that pure water is a simple combination of two gases, two molecules of hydrogen and one of oxygen, in nature you will rarely find the water in its pure form. From the chemistry point of view, for our coffee brewing, there are three other influential elements: Magnesium, Calcium and Bicarbonate (alkalinity). Water in nature also contains a lot of other elements, but from our point of view, those three are probably the most influential ones. It is worth mentioning also that often some chemical compounds are present. These usually cause unusual tastes, colours and even odours. That is why various methods of filtration are necessary to separate them.
As such, we can see, that brewing coffee is a game of balance. You might have a cup of excellence winning coffee that is perfectly roasted and prepare it on carefully designed brewers. Unfortunately, you might not have an adequate water to complete the brewing process. For example, hard or alkaline water will not directly harm flavour and aroma, but it will mute some of the natural acids in from your beans and produce a blander cup with less dry brightness.
If you are noticing that the coffee you brew is consistently flat, bitter or otherwise just not tastes right, the first think you will change will probably be the coffee beans. Not a bad place to start and probably there will be some effect out of it. But do not forget, around 98% of your beverage is water, so the flavour of it also matters a lot. Unfortunately, even local tap water can be taste-altering in unpleasant ways.
Firstly, do not use water, that you would not drink yourself. If this is a problem in your region, invest in a filter, that usually improves the water quality a lot and also decreases the presence of larger minerals. Besides that, cold water from the facet is usually fresher than the hot water and it more likely tastes cleaner to. So helping your kettle to heat the water faster, might not be such a good idea. Be sure, that the water you are using is always fresh, smell, look, and taste clean. Old, used and already heated and cooled water usually contains lower amount of oxygen, that contributes to water flavour, besides optimizes the way that the coffee and water react to one another.
Water hardness is directly related to the amount of calcium and magnesium in water. When there is too much of either of these metals in the water, the flavour will attach themselves. Forming solids, will decrease the amount of flavour of the beverage in your cup. Another important fact regarding hard water is that when heated, it creates limescale at a much faster rate than soft water does because of all of the minerals. This process can damage the system of your coffee machine quite quickly. It is possible to use water softeners, however most of them increase the level of salinity and consequently affect the flavour. You might test your water to see whether you actually need a softener. According to the Specialty Coffee Association of America, target sodium levels are about 10mg/L.1
Even a small quantity of Chlorine affects the flavour of your coffee so it is really necessary to avoid it during your coffee brewing process. One of the options is a carbon filter. Besides the alterations of the cup profile, it will make your coffee more acid, drastically reducing its pH balance. Chlorine also corrodes all the metallic parts of coffee machines and consequently shortening their life span.
It is indeed a very interesting and important part of a high-quality coffee preparation. The best baristas, such as Leonardo Gonçalves from Brazil and Maxwell Colonna-Dashwood from UK, are winning the contests also thanks to managing this detail. In case you want some more tips, you might test some of your own theory in practice and contribute to the coffee enthusiasts comunity. I going to test mine right now.