Coffee & Water – Why the water makes a difference

by Ryan Fair / Oct 17, 2018
Coffee & Water – Why the water makes a difference

The ultimate goal of this morning ritual is to create a perfectly balanced cup of coffee – the color, the taste and the smell (and the caffeine, let's be honest) are all criteria when judging that morning pick-me-up. In case the taste turns out to be flat, hollow, bitter, or vinegary, it is easy to assume that there is something wrong with the coffee beans or the brewing process. But is that where you should immediately turn to when figuring out how to perfect the cup?

Coffee is made up of over 98 percent of water

As it turns out, coffee is made up of over 98 percent of water.  That means that the quality of water has a significant role in the final coffee product.  


Wait, there is water in my coffee?

The transparent liquid H2O we are using as a base of all the coffee served hides a lot inside. Despite its transparency, there is a huge amount of solubles and solids in our tap water. This simple everyday consumable has a major effect on the quality of your cup of coffee. Also keep in mind: if the water is said to be of drinking quality, it might not be harmful for your health but can still contain some unpleasant substances that make your coffee taste flat or even bad, and more than likely has contaminants in it that should just not be in water at all (even though you might now taste them).

Coffee and water – Does my water matter?

Coffee brewing water should be clean and fresh by taste, smell and look. Also, it should be of food grade, and what’s more, there should not be chlorine, chloramine and hypochlorite in the water. These contaminants are added to most water supplies during the water treatment process in order to disinfect the water as it travels through the pipes. Chlorine (or it's byproducts) kill living things. Their goal is to kill bacteria and organisms in the water supply so we do not drink them. But that doesn't mean we should be drinking the Chlorine. 

It is good to remember that fresh, cold water is always the best starting point for brewing coffee. You don’t want to ruin a good cup of coffee by taking hot water out of the tap. Not only is hot tap water not fresh, it often has odd tastes and odors as the pipes tend to react more to hot water than they do to cold water.


What exactly is water? 

What is it in water that effects the taste or quality of our coffee? 

  • naturally occurring substances from soil, for example minerals and other organic substances (can be beneficial minerals and nutrients or harmful contaminants like Chromium 6, Mercury, or Arsenic)
  • substances from water treatment, for example chlorine, which is added to the main water pipes to maintain microbiological quality standards  
  • substances from the water supply system, for example copper and iron  
  • residues from pollution including pesticides and herbicides and radiological contamination 
  • microbes – harmless ones, but also bacteria and cysts 

Water Hardness and Coffee 

When the water meets carbonate rock containing magnesium carbonate and/or calcium carbonate, part of the water gains magnesium, calcium and bicarbonate ions. At Clearly Filtered we consider these "beneficial minerals" and our filters are designed to leave most of these in your water even after it is filtered. 

You have probably heard the phrase “water hardness”. Sounds simple, right? Either there are lots of minerals in the water, or there are not? Well, here is a bit more detailed information. 

Total Dissolved Solids can include these beneficial minerals or harmful contaminants like Chromium 6, Mercury, or Arsenic.

Hardness in general describes the amount of dissolved minerals in water. These dissolved minerals can also be called Total Dissolved Solids (TDS). Total Dissolved Solids can include these beneficial minerals or harmful contaminants like Chromium 6, Mercury, or Arsenic. That is why it is essential to have a filter that is smart enough to target the harmful contaminants while maintaining the beneficial minerals. Groundwater is harder than surface water because it has been in contact with minerals longer.


Total hardness (often measured as °dH): carbonate hardness + permanent hardness. In practice, this is the amount of Magnesium and Calcium ions.  

Magnesium and Calcium are helping to extract more taste, so we for sure want some of them in our water. Not just too much – and  only with a reasonable amount of bicarbonate. 

Magnesium makes a bit more powerful extraction than Calcium because a lot of flavorsome compounds are small and have a lot of oxygen in them. Magnesium likes these qualities. 

Calcium easily bonds with other substances. Together with carbonate hardness level, for example, it causes formation of limescale.
Magnesium is not easily bonding, so it rarely causes limescale formation.


Carbonate hardness kH: Bicarbonate and some other carbonates originated from carbonic acid that are pairing up with Magnesium and Calcium.  

Carbonate hardness is often quoted as temporary hardness. This actually makes sense, as boiling precipitates the minerals. When boiling water, the hardness is shifted from the water to the surfaces of the boiling equipment – for example a kettle or a coffee machine boiler. As a result, coffee machine valves can be clogged and achieving the right water temperature can be difficult.  

Carbonates, however, are the kings of coffee brewing water. If we forget about them, they will turn our great cup of coffee into a misery. 

  • In case there is high carbonate hardness in water, the positive acidity in taste (i.e. citric, fruity, sour etc.) will be flushed away by the pH buffer. The acidity itself is still there, we just don’t find it in the taste, only the earthiness and dull, flat taste.  
  • In case of low carbonate hardness the coffee taste is vinegary and sour. 

Sometimes carbonate hardness is referred to as alkalinity, which is the capacity of an aqueous solution to neutralize acid. Keep in mind that alkaline or base means something else!


Other dissolved ions: In addition to Magnesium, Calcium and carbonates that form the hardness of water, there are other dissolved ions contributing to the taste of water. These are for example Chromium 6, Mercury, Arsenic, Nitrite, Sodium, Potassium, Nitrate and Chloride. These other dissolved ions cause a risk of corrosion in high ranges. 

How does water affect coffee? Understanding the taste

So what does this mean?

Overall water content defines, and is essential, to the character of water and therefore the coffee brewed. 

Simply, you could say low overall mineral content is usually worse than high overall mineral content. Also, low carbonate hardness must be compensated by lowering the total hardness because we want to have a positive balance between the minerals. Furthermore, high total hardness will increase the weak acids in the cup, and high carbonate hardness leads to huge crust when cupping but also means more frequent descaling for the coffee equipment. 

At the end of the day, it is all about the balance between all the minerals in water. With the right kind and right amount of minerals in your water, you can get closer to creating the perfect cup of coffee. 


How does Clearly Filtered affect your water for coffee? 

Most tap water worldwide is too high both in carbonate hardness and in total hardness. It is essential that TDS exists in the water to brew a proper cup of coffee but it is also essential to understand which of the solids are left in the water when brewing. 

The Affinity Filtration Technology used by Clearly Filtered filters is very unique. It is smart enough to distinguish between the type of TDS in the tap water and will filter it if it is a harmful contaminant like Chromium 6, Mercury or Arsenic (there are many, many others as well) or it will maintain it if it is a beneficial mineral like calcium or magnesium. No other filter can do this. 

Most other water filters (like PUR and SOMA) do not remove the harmful solids and only work on affecting the taste or smell of the water. While other filters and systems like ZERO or Reverse Osmosis systems filter all Total Dissolved Solids leaving you with what the coffee and water industry terms as "dead water" or water that is lacking anything beneficial and most certainly water that SHOULD NOT be used for brewing coffee. 

The optimum level of TDS when brewing coffee ranges based on the brewer, the beans and the way it's being brewed, but it safe to say that water in the range of 120-160 parts per million is the optimum range for most instances. Low brew ratios (for example espresso compared to filter coffee) shift the optimum of total hardness and carbonate hardness towards higher values. There are no exact numbers and ratios to be given! 

With our water in Southern California, we constantly see our TDS after filtration hover around the 120-135ppm mark. This gives us the optimum level of TDS for brewing coffee. 

Shop the Pitcher

Shop the 3-Stage Under the Sink Filter System

Shop the Universal Fridge Filter