The Best Water for Coffee: Hardness, Alkalinity and What Studies Found

By Mike Cullen, Founder · Published November 3, 2026

Key takeaway: The best water for coffee is clean, odor-free and chlorine-free, with a moderate amount of minerals. A 2026 sensory study found alkalinity (bicarbonate) changed coffee flavor far more than hardness did: more bicarbonate meant less perceived acidity and fruitiness and more bitter, roasted notes. Aim for the Specialty Coffee Association's alkalinity target of about 40 ppm.

You picked great beans. You dialed in your grind. You even weighed your coffee. Then you filled the kettle straight from the tap without a second thought.

Here's the twist: a cup of coffee is mostly water, and what's dissolved in that water quietly changes what ends up in your mug. Let's look at what the chemistry and taste studies actually found.

Does water really change how coffee tastes?

Yes. Water isn't just a delivery truck for coffee flavor. Minerals in water, like calcium, magnesium and sodium, interact with the compounds in coffee. Chemists at the University of Bath used computer modeling to measure how strongly these dissolved ions bind to five common coffee acids, caffeine and a flavor compound called eugenol, and concluded that the mineral content of water helps explain why different waters extract coffee differently (Hendon et al., J Agric Food Chem 2014).

That was a model. The fun part is what happened when people actually tasted the coffee.

Hardness vs alkalinity: which one matters more?

First, two quick definitions:

• Hardness is mostly the calcium and magnesium in your water. It's what leaves white scale in your kettle.
• Alkalinity is mostly bicarbonate. It's the water's ability to neutralize acid, which is why it's sometimes called "buffer."

A 2026 study at the University of Copenhagen brewed the same Colombian coffee with ultrapure water, then with added calcium, magnesium and bicarbonate, and ran trained taste tests. The results were surprisingly clear (Rune et al., J Food Sci 2026):

The authors' bottom line: under their test conditions, alkalinity, not hardness, was the main driver of flavor changes. A separate 2024 Swedish study pointed the same way for hardness. Adding magnesium and calcium salts at levels typical of drinking water caused only limited changes in the citric, malic, lactic and quinic acids extracted, while ten-fold higher levels made a bigger difference (Bratthäll et al., Heliyon 2024).

So if your coffee tastes flat, dull or extra bitter no matter what you do, high-alkalinity water is a suspect worth checking.

What does the SCA recommend for coffee water?

The Specialty Coffee Association publishes a water standard for brewing. Here are the numbers from its 2018 Coffee Standards (SCA Coffee Standards, §4.1):

Notice that alkalinity gets the tightest window. That lines up nicely with the Copenhagen taste results.

Is distilled or reverse osmosis water good for coffee?

By the SCA's numbers, water with almost no minerals falls below its targets for both hardness and alkalinity. Very pure water was useful in the Copenhagen study as a clean baseline, but it isn't what the brewing standard aims for.

One more practical note: if you're filling an espresso machine, follow the manufacturer's water guidance first. Very soft water and very hard water can both matter for the machine itself, not just the taste.

Tap, filtered or bottled: what should you use?

Here's a simple, no-lab-coat game plan:

1. Start with the smell test. If your tap water smells like a swimming pool, that chlorine will follow it into your cup. The SCA standard calls for none.
2. Try a carbon filter pitcher. It's the easy, common way to cut chlorine taste. Check the label for chlorine taste and odor reduction.
3. Look up your water report. In the U.S., community water systems publish an annual water quality report, called a Consumer Confidence Report (EPA). Many list hardness. If yours doesn't show alkalinity, inexpensive aquarium or pool test strips can give you a ballpark.
4. Run a taste test. Brew the same coffee two ways, with your filtered tap water and with a bottled water, and taste side by side. Keep the ratio and grind identical (our coffee to water ratio cheat sheet and grind size chart help).
5. If it tastes flat or harsh, suspect alkalinity. Bottled waters list their minerals on the label or the brand's website, so you can look for one closer to the SCA ranges.

Water matters for every brew method, from pour-over to French press.

Why does water matter more for some coffees than others?

Bicarbonate's big effect in the study was muting acidity and fruitiness. So brighter, lighter roasts with lots of fruity acidity may show the difference most. Medium roasts like ours lean toward chocolate and caramel, but good water still keeps the cup sweet and balanced instead of flat. Want the roast side of the story? See light vs medium vs dark roast.

Clean water, clean beans

We care about what goes into your cup, starting with the beans. That's why we started Edge in St. Paul in 2020. Pure Health Coffee is a Peruvian single-origin Arabica, medium roasted for notes of chocolate, caramel and roasted nuts. Every lot is tested by Eurofins, and our posted sample reports showed no detectable mycotoxins, including ochratoxin A below 1 ppb. See them on our lab results page, and learn what we test for on our mold-free coffee page. Results apply to the samples tested.

Pair clean beans with good water and you've handled the two biggest ingredients in your cup. Shipping is free on every order, always.

FAQ

What is the best water for coffee? Clean, odor-free, chlorine-free water with moderate minerals. The Specialty Coffee Association targets calcium hardness of 50 to 175 ppm, alkalinity around 40 ppm and a pH near 7.

Does water affect the taste of coffee? Yes. A 2026 University of Copenhagen sensory study found that adding bicarbonate to brewing water reduced perceived acidity, fruitiness and complexity and increased roasted and bitter notes.

Is hard water bad for coffee? In the 2026 study, hardness alone produced no marked flavor changes, even at high calcium levels. Alkalinity mattered much more. Very hard water can still leave scale in kettles and coffee machines.

Can I use distilled water for coffee? Distilled water has almost no minerals, so it falls below the Specialty Coffee Association's targets for hardness and alkalinity. For espresso machines, follow the manufacturer's water guidance.

Is filtered water better for coffee? A carbon filter is a common way to reduce chlorine taste and odor, and the SCA standard calls for no chlorine in brewing water. Filtering doesn't necessarily change alkalinity, so a side-by-side taste test is the best check.

How can I find out what's in my tap water? In the U.S., community water systems publish an annual water quality report called a Consumer Confidence Report. Many list hardness, and simple test strips can estimate hardness and alkalinity at home.

This article is general information about coffee brewing and water chemistry research. Results from individual studies apply to the coffees and conditions they tested. For questions about the safety of your drinking water, contact your local water utility.

Sources

1. Hendon CH, Colonna-Dashwood L, Colonna-Dashwood M. The role of dissolved cations in coffee extraction. J Agric Food Chem. 2014;62(21):4947-4950. https://pubmed.ncbi.nlm.nih.gov/24802110/
2. Rune CJB, Steen I, Kjærgaard ER, Maroun Z, Bredie WLP, Kjaergaard HG. Impact of water composition on coffee sensory properties: a comprehensive analysis. J Food Sci. 2026;91(9):e71434. https://pubmed.ncbi.nlm.nih.gov/42746805/
3. Bratthäll T, Figueira J, Nording ML. Influence of divalent cations on the extraction of organic acids in coffee determined by GC-MS and NMR. Heliyon. 2024;10(5):e26625. https://pubmed.ncbi.nlm.nih.gov/38434259/
4. Specialty Coffee Association. Coffee Standards (revised 2018), §4.1 Water for Brewing Standards. https://sca.coffee/research/coffee-standards
5. U.S. Environmental Protection Agency. Consumer Confidence Reports (CCR). https://www.epa.gov/ccr
6. Edge Coffee sample Eurofins report AR-24-JF-015481-01 (Pure Health Coffee green beans, Mar 2024), via /pages/lab-results