What Is the Best Water for Brewing Coffee? The 98% Nobody Talks About

The Briefing: Declassified Series // Issue 14

You spent time choosing the right coffee. You paid attention to the roast, the origin, the grind. Then you filled the kettle from the tap and brewed it, and wondered why the cup did not quite deliver. The answer is almost always the water. To find the best water for brewing coffee, you have to start with a number most people have never heard: ninety-eight.

A brewed cup of coffee is, by mass, approximately 98.5-99% water. The dissolved solids, acids, and aromatic compounds that make coffee taste like coffee account for roughly one to two percent. Which means water is not the backdrop. It is the main ingredient. Whatever your water tastes like, carries, or lacks, that character shows up in the cup at scale.

This is the variable the coffee industry rarely advertises, because selling you a water recommendation does not move product. But ignoring it quietly ruins thousands of good cups every day. Here is what the data says.

Consider this your briefing.

How much of a cup of coffee is water?

The 98% figure is not marketing copy. It reflects the basic physics of extraction. When hot water passes through ground coffee, it pulls out soluble compounds: acids, sugars, lipids, chlorogenic acids, caffeine, and the volatile aromatics that your nose registers before your mouth does. Those dissolved compounds are suspended in water. The water is the carrier fluid, the solvent, and the delivery mechanism all at once.

This matters because the quality of a solvent affects what it dissolves, how efficiently it dissolves it, and what it contributes on its own. Water that carries off-flavors will donate those off-flavors to the extraction. Water that lacks the right mineral content will extract unevenly. Water that is too mineralized will interfere with the process in the opposite direction. In each case, the cup reflects the water, not just the coffee.

It also matters for equipment. Water quality affects scale buildup in boilers, heating elements, and group heads. Scale is not just a maintenance issue. It changes temperature consistency and flow rate, which changes extraction, which changes what ends up in your cup.

Rule: Ninety-eight percent is not a rounding error. Treat water as an ingredient, not a utility.

What is the best water for brewing coffee?

The Specialty Coffee Association publishes a water quality standard that answers this question with measurable targets. The SCA standard identifies the variables that most directly affect extraction and cup quality: total dissolved solids, pH, chlorine, and a handful of mineral thresholds.

The SCA's target for total dissolved solids is approximately 150 mg/L, with an acceptable range around it. Total dissolved solids, or TDS, is a measure of the mineral and ionic content suspended in water. Too low, and the water behaves more like a pure solvent that strips compounds aggressively and extracts unevenly. Too high, and the minerals compete with or interfere with the compounds you want extracted. The target represents a middle zone where extraction is balanced and the water contributes clean minerality without dominating.

pH should be close to neutral, around 7. Very acidic water can over-emphasize the acidic notes in coffee. Very alkaline water can mute them and leave the cup tasting flat or soapy.

Chlorine content should be zero, or as close to it as possible. Most municipal tap water is treated with chlorine or chloramines. Both are disinfectants, and both have detectable flavors and odors that carry directly into brewed coffee.

Rule: The SCA target is not a preference. It is an engineering spec for what water allows coffee to do its job.

What does hard or soft water do to the taste?

Water hardness is a measure of calcium and magnesium ion concentration. Both minerals play a role in extraction, but at excess levels they cause problems the palate registers immediately.

Hard water, water with high mineral content, can over-extract certain bitter compounds while under-extracting the acids and sugars that give coffee its brightness and sweetness. The result is a cup that tastes dull on the front and harsh on the back. Hard water also accelerates scale formation in equipment, which compounds the problem over time.

Very soft water, water with almost no dissolved minerals, presents the opposite issue. Minerals help structure the extraction. Without them, water behaves erratically as a solvent. The extraction tends to be uneven, pulling some compounds too aggressively while leaving others behind. Distilled or deionized water, which has had virtually all dissolved solids removed, produces notoriously flat, lifeless coffee despite using the same beans and the same grind.

The practical takeaway is that neither extreme serves you. Water that is too hard over-mineralizes the cup and wears out your equipment. Water that is too pure under-extracts and tastes empty. The target range the SCA identifies exists precisely because the sweet spot is real and narrow enough to matter.

Rule: Hard water and distilled water both fail at extraction. The answer is filtered water in the right mineral range, not simply "pure" water.

Does tap water ruin coffee?

That depends on where you live and what your utility adds to it. Municipal tap water varies significantly by city and region. Some tap water falls reasonably close to the SCA target. Much of it does not, and the most common reasons are chlorine treatment and inconsistent mineral content.

Chlorine is added to municipal water supplies for public health reasons that are entirely legitimate. But the same properties that make chlorine effective as a disinfectant make it disruptive in brewed coffee. It reacts with organic compounds in coffee during brewing, producing off-flavors that range from medicinal to papery to just "wrong." The effect is more pronounced with lighter roasts, where the subtle aromatics are easier to disturb.

Chloramines, which are increasingly common as a more stable alternative to chlorine in municipal treatment, are harder to remove than chlorine. Standard activated carbon filters remove chlorine readily. Chloramines require a longer contact time or a catalytic carbon filter. If your tap water uses chloramines and you are using a basic countertop filter, you may still be getting chloramine interference in the cup.

Well water introduces a different set of variables, typically higher hardness and occasional sulfur or iron content, depending on local geology.

Rule: Taste your tap water before you brew with it. If it has any detectable flavor or odor, so will your coffee.

What filtration actually helps?

The goal is not to remove everything from your water. It is to remove the things that do not belong while preserving or achieving the mineral balance that extraction needs.

Activated carbon filtration is the baseline. It removes chlorine, many volatile organic compounds, and improves taste and odor for most municipal tap water. It does not significantly change TDS or mineral content, which means if your tap water is already in a reasonable mineral range, carbon filtration may be sufficient.

If your water is very hard, a mixed-bed filter or a reverse osmosis system can bring TDS down, but reverse osmosis removes nearly everything, which puts you back in the too-soft territory. Many coffee-focused RO setups add a remineralization stage specifically to reintroduce the minerals the membrane stripped out, targeting the SCA range on the way back up.

Pitcher filters vary widely in what they actually remove. Check the specific filter's testing data, not just the marketing language on the box.

Bottled water is a workable short-term option if you check the label's mineral content. Some bottled spring waters fall close to the SCA target; others are too hard or too soft. Distilled or purified water marketed as pure is generally too low in TDS to extract well without remineralization.

Rule: Match the filtration method to the problem your specific water has. "Filtered" is not a single category.

Why does LACC care about your water?

Legendary Aviation Coffee's job ends at the roaster. Every bag that ships is 100% Arabica, sourced with an 85-point SCA floor and verified through an independent Q Grader at the importer stage. The beans go through a Loring S35 Kestrel, a smokeless convection air roaster, at a bean temperature ceiling below 430 degrees Fahrenheit, before Second Crack and the back of full medium. That roast ceiling is where LACC stays to preserve the bean's natural undertones and keep the origin character in the cup.

The point of that process is to deliver a clean cup with nothing to hide, where the characteristics of the origin and the roast can actually be tasted. But none of that work shows up correctly if the water does not cooperate.

An 85-point-floor coffee is a coffee with measurable, graded characteristics: specific acidity, sweetness, body, and finish scores that qualified graders documented under controlled conditions. Those characteristics exist in the bean. Whether they make it into the cup depends on the extraction environment, and the extraction environment is mostly water.

Good water lets the roast speak. Poor water muffles it, distorts it, or replaces it with chlorine flavor and mineral bitterness. LACC cannot control what comes out of your tap. But understanding why water matters is part of the briefing, because the goal is a cup that actually reflects the coffee in the bag.

Start with filtered water at the right mineral range. Use what comes closest to the SCA target you can practically access. Your equipment will scale less, your extractions will run cleaner, and the 2% of your cup that is coffee will finally have a chance to do what it was roasted to do.

The 98% has been there the whole time. Now you know what to do with it.

See it in the cup. Explore the specialty-grade coffee fleet, the Boujee Bomb loose-leaf teas, and the Superbly Simple Syrups.

Fly with better data.