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It’s no secret that coffee geeks obsess with every detail of brewing the perfect cup of coffee. From the type of beans to the grind size, there are a million things that can affect the end result. But one factor that often gets overlooked is water quality.

In this blog post, we’ll take a look at why water matters when it comes to coffee, and how you can make sure you’re using the best possible water for your brew.

Water is the second most important ingredient in coffee

Water quality is essential for coffee brewing and long-lasting coffee gear. In the picture, a glass of water.
Photo by Manki Kim on Unsplash

Water makes up 98-99% of your cup, so it’s no surprise that water quality has a big impact on taste. 

Water solves coffee’s flavorful and aromatic compounds. Without its power, coffee brewing can’t happen. That’s why the purity and mineral content of water plays a huge role in coffee taste.

Extraction is also affected by water temperature. Generally, hotter water extracts more flavors from the coffee grounds. As a result, you get a bolder cup of coffee. 

If your coffee tastes weak or watered down, it could be because the water you’re using is too cold.

In sum, there are two key aspects in the water you can play with: hardness and temperature.

What is water hardness and why does it matter

Water hardness is a measure of the concentration of minerals in the water, and it can vary from city to city. In general, the harder the water, the more minerals it contains.

It’s adequate to measure total dissolved solids (TDS) to estimate water hardness, but they aren’t the same. TDS measures inorganic solids dissolved in water. In other words, TDS accounts for a wider range of elements in water, not only those contributing to water hardness.

The Specialty Coffee Association (SCA) Heritage Standard is between 75 – 250 mg/L for TDS in water. Yet, more recent research on SCA water quality standards for coffee brewing suggests a more detailed examination.

A recent study from Ege University has found that hard water enhances coffee bitterness, and the best taste comes from medium-hard water.

Water typeTotal Dissolved Solids (TDS)
Bottled water60 ppm
Purified water24 ppm
Medium-hard water141 ppm
Hard water424 ppm
Types of water used to determine the best water hardness for coffee brewing.
Source: Dadalı, C., Elmacı Y., 2021. The Effect of Water Hardness on Volatile Compounds and Flavour of Filter Coffee,  Turkish Journal of Agriculture – Food Science and Technology, 9(2): 312-320, DOI: https://doi.org/10.24925/turjaf.v9i2.312-320.3885

Let me be clear. Hard water isn’t unsanitary or dangerous. It influences coffee extraction by changing water’s ability to dissolve coffee. For this reason, plumbed coffee machines use water filtration systems. Furthermore, many experts recommend using mineral supplements to create tailored water recipes. And that is, of course, the geekiest you can get with water and coffee.

As a general rule, it’s better to use bottled or filtered water to brew coffee than tap water. First, tap water contains chemicals that alter the coffee taste. Second, minerals in tap water can be too high, leading to an undesirable level of water hardness for coffee brewing. And finally, hard water leaves mineral residues in your machine, leading to shorter cycles for descaling.

Examples of TDS levels in fine bottled water

Water brandTotal dissolved solids (TDS)
Evian345 ppm
Fiji Water222 ppm
Acqua Panna150 ppm
Total dissolved solids in fine bottled water brands, according to their public information

Water temperature in coffee brewing

The temperature of the water is important when you are making coffee. The chemical reaction that happens will

The temperature of the water is important when you are making coffee. The chemical reaction that happens will break down the coffee solubles. Moreover, temperature affects the extraction speed.

For instance, cold brew coffee takes 12-24 hours to make, while regular coffee takes minutes and espresso takes seconds.

If the water is too hot, it will extract too much bitterness from the grounds. If the water is too cold, it won’t extract enough flavor. According to Specialty Coffee Association, the best temperature for brewing coffee is somewhere between 195-205 degrees F (91-96 degrees C).

Still, many coffee drinkers prefer boiling water, since it provides a more intense and hotter cup of coffee. The main reason why the SCA suggests a lower temperature is because of the flavors and aromas in high-quality coffee beans.

In sum, many of coffee’s most delicate flavors and aromas are impossible to perceive while coffee is scorching hot. Moreover, most flavors that come out of coffee when water is boiling are on the bitter end of the spectrum.

Beyond water hardness: other indicators of water quality

Besides temperature and hardness, there are other factors that can affect the taste of coffee. These include:

  • Alkalinity or pH level
  • Chlorine levels
  • Dissolved oxygen levels

Although these factors are less important than temperature and hardness, they can still have an impact on the taste of coffee. For example, high levels of chlorine add an unpleasant flavor to the cup. Moreover, the pH of water can alter the natural acidity we perceive in coffee. Finally, most research suggests that high levels of dissolved oxygen improve water quality and taste.

How to test your water’s quality at home

So what’s a coffee geek to do?

If you’re concerned about the quality of your water, there are a few things you can do to test its purity. You can use a water quality test strip to measure alkalinity and chlorine levels.

Many espresso and coffee geeks get a refractometer to analyze extraction, as well as their water quality. It’s quite interesting to learn more about it. Furthermore, Professor Dr. Yeşim Elmacı from Ege University, suggests using a refractometer as a feasible home alternative.

Another way to test your water is to send it in for water analysis. This will give you a more detailed breakdown of the water’s chemical composition.

If you’re not happy with the results, you can try filtering your water or using bottled water.

All of these factors are important to consider when it comes to overall water quality. By using the best possible water, you’ll be one step closer to making the perfect cup of coffee.

Super Coffee Geek Water Tips

If you are in a mad scientist mood, you’d love to experiment with a few gadgets and geeky tricks. But what’s a coffee geek to do if they want to get serious about water?

  • Use filtered or bottled water whenever possible. This will help to remove impurities and improve the taste of your coffee.
  • Consider the TDS values displayed on bottled water labels. Choose medium-hard water (around 141 ppm), price isn’t a good reference here. Fine waters tend to be harder than regular ones.
  • Get a TDS meter and measure coffee extraction and water TDS
  • Measure your water hardness, alkalinity, and chlorine content with water test strips
  • Create your own water recipes
  • Invest in a good water filtration system. This will help to improve the quality of your tap water and ensure that you’re using the best possible water for coffee brewing.


Thanks to Professor Dr. Yeşim Elmacı from Ege University for providing scientific research information for this blog post.

The article The Effect of Water Hardness on Volatile Compounds and Flavour of Filter Coffee was very helpful to write this blog post.

For proper referencing, you can follow the appropriate standards required by your institution, or as follows:

Dadalı, C., Elmacı Y., 2021. The Effect of Water Hardness on Volatile Compounds and Flavour of Filter Coffee,  Turkish Journal of Agriculture – Food Science and Technology, 9(2): 312-320, DOI: https://doi.org/10.24925/turjaf.v9i2.312-320.3885

The featured image for this blog post is a photo by Clint Bustrillos on Unsplash.

Further reading

Best Gooseneck Kettle

Water Temperature: Does it matter for drip and pour-over coffee brewing?

I fell in love with coffee before I could even read, and my passion for this elixir has shaped my entire life. Through research and learning, I honed my knowledge of specialty coffee and espresso culture by seeking the advice of the most prominent coffee experts and researchers. I have been fortunate enough to meet inspiring individuals, expand my knowledge, and cover exciting coffee-related topics in my writing. My skill in translating complex facts into a reader-friendly style caters to coffee connoisseurs and newbie enthusiasts alike, so everyone can fully appreciate the richness and diversity of the world of coffee.
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