Water is the main ingredient in your coffee.

Not only is it the main ingredient but it also serves as a solvent to extract coffee flavor compounds from the beans. To say it is an important variable is an understatement.

I didn’t start drinking coffee until after I graduated college so my first steps into the world of coffee were those with a fresh and unbiased perspective. My degree was in engineering and this led me to take somewhat of an analytical approach to my new hobby. 

After reading any literature I could get my hands on and learning about the importance of the green bean, grind size selection, and numerous other variables, I was shocked that a lot of educational content left out a discussion of what water your should use. It seemed obvious to me that this variable was as important as any of the others, yet attention given to this variable was far less. 

After a few years of study I feel confident in my understanding of water for coffee. Below is a summary of what I have learned on my coffee journey. It has been essential in helping me take my home brews from “pretty good” to “so amazing I’d rather brew at home than go to the local cafe” and I hope it can do the same for you. 

What’s in tap water?

Tap water sources contain minerals and salts as well as a variety of chemicals and metals that are often the consequence of manufacturing or waste disposal. Water treatment plants use a sequence of treatment methods such as sedimentation, filtration, and chemical additives to remove the bulk of harmful or unpleasant substances. 

From a cost perspective, it is only possible to remove the majority of these substances and the tap water we are left with usually contains a significant amount of minerals and salts as well as trace amounts of toxins like arsenic, pesticides, pharmaceuticals, etc. 

Your local municipality monitors the levels of toxins in the water to ensure that they are all within a “safe” range for that toxin. In fact, this information is almost always readily available on your local governments website. 

Water variables that affect coffee flavor

As far as our brews are concerned, there are three main variables of your water that will have a significant impact on our cup quality. 

  • Hardness: also referred to as total hardness or KH, this variable plays a critical role on how good of a solvent your water is for coffee flavor compounds. Generally speaking, the harder the water the more coffee compounds your water will extract from roast and ground beans. Hardness comes from Magnesium (Mg) and Calcium (Ca) cations. 
  • Alkalinity: Also refereed to as GH and not to be confused with the term “alkaline”, meaning a basic solution, alkalinity refers to the ability for water to buffer changes in acidity. The most common sources are carbonates (CO3, KHCO3, NaHCO3). 
  • Odor/taste: While not necessarily as specific of a variable as the two above, your water should be free of any unpleasant taste and odor as this could negatively impact your end beverage. Chlorine which is used to kill bacteria in our tap water often still remains and can lead to an unpleasant taste and odor. 

The SCA’s water for coffee guidelines

A good place to start in our journey to acquire the best water possible for brewing coffee would be to look to the SCA’s “water for brewing standards.” They are as follows:

  • Free of Chlorine
  • Clean fresh/odor free
  • Calcium hardness of 50-175 ppm as CaCO3 equivalent
  • Alkalinity of 40-70 ppm as CaCO3 equivalent
  • PH: 7 with an acceptable range of 6-8

Most hard tap water is going to be anywhere from 200-500 ppm as CaCO3 equivalent calcium and magnesium hardness with a highly variable alkalinity. The result of brewing with this water is bitter and heavy coffee, due to over extraction. It will also likely be flat tasting, assuming there is high alkalinity, causing your end beverage to be a basic solution (above a PH of 7). 

If you live in an area with soft water, meaning you water has a total hardness of less than 60 ppm as CaCO3, you will most likely end up with a brew that is weak in flavor due to a lack of extraction. 

How does water change coffee’s flavor?

The graph above shows a simplification of the effect of both hardness and alkalinity on coffee. Increasing hardness causes us to extract more compounds from our coffee and when using a high quality coffee extracts more of the highly desired fruit flavors.

There is, however, a catch; if we extract too much we will also be pulling out undesirable flavors. Different flavors are extracted at different stages in your brew, meaning that there is a sweet spot (pun intended) at which we want to stop extracting in order to get a brew that is balanced.  

The alkalinity of our water changes the acidity of our end brew. Roast and ground coffee contain CO2 and when we brew some of this is released into the air but some is also pulled into our beverage. The CO2 reacts with the water and increases the acidity. There are also acids in the bean itself that contribute to the acidity of our end beverage. 

Too much acidity causes our brew to taste sour and sharp while too little will cause it to taste flat.  

How do I get the best water for my Coffee?

There are two ways to go about crafting water for coffee. One is to treat your existing tap water and the other is to re-mineralized distilled or reverse osmosis water. For the purposes of this article, I am only going to discuss the latter as the former can be much more complicated due to the fact that you need to first know what you existing water contains and then treat it in the appropriate manner by removing the stuff you don’t want and then adding back in stuff that you do. 

If you are set on treating your existing tap water, I would recommend checking out  Peak Water. The creators are incredibly knowledgeable about water for coffee and served as an important source for my own education on the topic. 

In contrast to the complicated process of starting with tap water or treated water, when using distilled water we are given a blank canvas with which we can create our very own masterpiece. To actually do this, we simply choose our ingredients and add them in the right amount to our water.

Sounds easy right? Unfortunately, there is some math required to know how much of each mineral to add to your distilled water. I may go in depth into this in a different article but the unit conversions (there are way to many ways to measure hardness and alkalinity) can cause things to be slightly confusing if it’s been a long time since you’ve taken chemistry 101. 

In order to avoid all the math and hassle of buying and measuring out your own minerals, you can use Lotus Water which contains pre dissolved minerals that are added to distilled water using precision droppers. The solutions are formulated such that adding a single drop of magnesium or calcium to 500 mL of distilled water, the supplied bottle filled to just below the cap, adds 30 ppm as CaCO3 of hardness and adding a drop of bicarbonate adds 15 ppm as CaCO3 of alkalinity. 

(disclaimer: I am the founder of Lotus Coffee and am therefore biased towards my own product) 

Dialing in your water

Lotus Water comes with three different ingredients for your water. One bottle of Calcium concentrate, one bottle of Magnesium concentrate, and one bottle of Potassium-Bicarbonate concentrate. 

A wonderful study carried out by Christopher Herndon and Colonna Dashwood (creators of Peak Water) discusses the roles of both magnesium and calcium cations regarding their ability to target the extraction of specific coffee compounds.

If you’re not interested in reading the paper yourself, a quick summary is that magnesium is generally speaking a more powerful extractor than calcium. This is confirmed in my own taste testing in that when I brew with waters containing mostly calcium for hardness I tend to get a brighter and sweeter cup. Magnesium on the other hand adds body, mouthfeel, and can introduce a small amount of bitterness to cut an overpowering amount of sweetness. 

To start dialing in a new coffee, I usually brew a cup with equal parts magnesium and calcium and a 2:1 ratio of hardness (Mg and Ca) to alkalinity (potassium bicarbonate). If the brew lacked body, I add an additional drop of magnesium and try again. If it’s lacking in sweetness I add calcium. If the cup was overpowering I simply reduce the overall hardness all while maintaining my ratio of hardness to alkalinity. 

The point is that by using water instead of grind size to dial in your cup, your ability to manipulate the flavor is increased and the process is simplified. This also allows you to create bespoke waters that highlight the flavors of the specific coffee you are brewing and target the flavors that you want in your coffee. 

Is bespoke water really worth all the trouble?

When I first started to brew coffee at home I was so excited by the thought that I would be able to brew coffee with a flavor profile that fit my own preferences. I was equally surprised when that first cup of coffee tasted absolutely horrible. I tried to convince myself that it was a good first attempt but quickly gave in and tossed the cup after a couple more sips. 

After visiting forums, reading books, and purchasing more coffee gear, I continued pursuing that cafe quality cup I so desired to drink on a Sunday morning in the privacy of my own home. After quite a bit of tinkering I was 90% of the way there. I could consistently brew coffee that tasted “pretty good.” I am not the kind of person to stop at 90% though. 

When I first started experimenting with water I immediately knew that it was the last piece of the puzzle that I was missing. There was even a time that I visited my in-laws and quite literally packed some of my homemade water to use in their brewer. I can now confidently say that I make coffee most cafes should be striving to match it under the additional constraints of brewing in that setting. 

So when you ask yourself, “is crafting my own water worth it?” I assure you, the question after you do will instead be, “can I ever go back?”