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Coffee and Water: The Importance of High-Quality Water in Brewing

Making great coffee might be an art, but in the end, it all comes down to science. If you want to get the best from your coffee, you need to consider exactly what goes into it, and most of that is water.

But what makes water good or bad for brewing? Here’s what you need to know.

The link between good coffee and water

Prepared coffee is between 98% and 99% water. So it makes sense that if you start with bad water, you’re going to end up with a bad cup of coffee.

When you consider what makes bad drinking water, you tend to think about water with impurities. In tap water, things you often encounter include chlorine leftover from the water treatment process, various metals from old plumbing, and microbes (1).

But there’s a little more to it than that. The brewing itself is a chemical process, so the chemical makeup of the water will also impact your final cup of coffee. This is where hardness and pH levels come in. These all affect the smell and taste of the water, which in turn affects the flavour of your coffee.

Water hardness and pH levels

Even if you’ve never delved into the science of it, you’ve probably heard about hard water and soft water. Simply put, hard water has a high mineral content, whereas soft water has little to no minerals. These minerals, namely calcium and magnesium, enter the water naturally as it flows over rocks such as limestone.

Home baristas are often advised to avoid hard water, as the mineral content can wreak havoc with coffee makers. The calcium, as calcium carbonate precipitate, is what we know as limescale (2).

So is soft water the answer? Not as far as a good cup of coffee is concerned. It’s these minerals that help extract flavour from your coffee. Without them, you’ll have a flat, lifeless drink. Water hardness is also tied to the pH level. Naturally, soft water is more acidic, which can cause corrosion damage to your equipment (3).

ph water scale and importance of high quality water for brewing
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The best water for brewing coffee

The SCA has developed standards for water when cupping specialty coffee. It should be clean, odour-free, chlorine-free, with a pH level of 7 and a calcium content of 50-175 ppm (4). But how do you recreate this water for coffee at home?

There are essentially three things to keep in mind when choosing a water formulation: longevity of brewing equipment, sensory quality, and drinking safety.

The most important thing is knowing what kind of water you’re working with. This way you can compensate for any levels that skew too far in one direction.

Filtered tap water – A water filter is one of the easiest ways to clean up impurities, whether it’s in your machine or attached to the tap. A good filter will remove not only sediment but also chemicals such as chlorine. If you’re using a machine with a water line, you should ensure that the system has a built-in filter as well.

A filter is the best solution if the hardness and pH of your tap water are close to what you want.

Bottled water – Apart from the apparent cost and waste involved, bottled water is not suitable for coffee. While every brand is different (which can be a problem), bottled waters tend to be either very high in minerals or very low.

Distilled water – Despite being the purest option, distilled water is not a good idea for coffee. All of the impurities are removed, but so are the minerals vital for flavour. There is also a pH issue. Distilled water has a pH of 7 at the distilling. But this will drop to up to 5.5 after exposure to air (5).

Reverse osmosis – This is considered the height of water filtration, but you need to be careful about what system you use. Older RO systems take out all of the impurities, including minerals, which will leave you with water that’s no good or coffee. More modern reverse osmosis systems contain a remineralisation system, which adds back beneficial amounts of magnesium and calcium.


You can microwave water for coffee, but we don’t recommend it. The main issue is that this method doesn’t heat the water evenly (6), which is an issue for nailing the perfect brewing temperature.

You should descale your coffee maker monthly. However, it does depend on how much you use it and what kind of water you use. If you see any white film on your equipment, it’s definitely time to descale.

Your coffee could be bitter for many reasons. The most common cause is over-extraction, but it could also be due to dirty equipment, stale beans, or poor water quality.

  1. Four types of contaminants in drinking water. Aquaporin. (2021, July 20). Retrieved September 21, 2021, from https://aquaporin.com/contaminants-drinking-water/
  2. Donahue, C. (2019, March 2). Pros & cons of a water softener. Sciencing. Retrieved September 21, 2021, from https://sciencing.com/pros-cons-water-softener-5470633.html
  3. Poczatek , B., & Yeggy, E. (2019, March 15). Water softeners and corrosion. WCP Online. Retrieved September 21, 2021, from https://wcponline.com/2019/03/15/water-softeners-and-corrosion/
  4. Coffee Standards. Specialty Coffee Association. (n.d.). Retrieved September 21, 2021, from https://sca.coffee/research/coffee-standards
  5. Bell-Young, L. (2020, September 8). What is the pH of Distilled water?: The Chemistry Blog. ReAgent Chemicals. Retrieved September 21, 2021, from https://www.chemicals.co.uk/blog/ph-of-distilled-water
  6. Bantilan, C. (2019, November 6). Can you boil water in the microwave, and should you? Healthline. Retrieved September 21, 2021, from https://www.healthline.com/nutrition/boil-water-in-microwave
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Growing up in a coffee-free household, the discovery of the Moka pot as a teen
was something of a revelation. I’ve now upgraded to the AeroPress for my daily
brew, with a Hario V60 on hand for lazy weekend mornings.

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