Why Water Quality Matters More Than You Think
Coffee is, by mass, almost entirely water. A typical cup contains roughly 98 to 99 percent water, with the dissolved coffee solids making up the rest. That tiny percentage carries all the flavor, but the water itself is the solvent, the transport mechanism, and in many cases the limiting factor in how much flavor you can actually pull out of your beans.
Walk into any specialty café and you will find baristas obsessing over grind size, bloom timing, and pulse pours. Yet many of those same shops use whatever water happens to come out of the tap, filtered through a generic cartridge. This is one of the most overlooked variables in pour-over brewing. Whether you brew on a Hario V60, an Origami, a Kalita Wave, or a Chemex, the water you pour into the dripper sets a hard ceiling on the cup quality.
Three numbers describe most of what matters: TDS (total dissolved solids), GH (general hardness), and KH (alkalinity, sometimes called carbonate hardness). Understanding what each one does is the first step toward brewing with intention rather than luck.
TDS: The Total Picture
TDS stands for Total Dissolved Solids, and it is usually expressed in parts per million (ppm) or milligrams per liter (mg/L), which are equivalent. It measures every dissolved compound in your water, minerals, salts, organic matter, all of it.
The Specialty Coffee Association has historically suggested a target range of roughly 75 to 250 ppm for brewing water, with around 150 ppm often cited as a sweet spot. This is a guideline rather than a law. Water below 50 ppm tends to taste flat and can over-extract bitterness, while water above 300 ppm often mutes acidity and leaves drinks tasting dull or chalky.
A common rule of thumb among home brewers: if your water tastes great straight from the glass, your coffee has a much better chance of tasting great too.
You can measure TDS with an inexpensive handheld meter, which costs less than most decent grinders. The reading will not tell you what is dissolved in your water, but it gives you a single useful number to compare against your brew results.
Actionable Tip
Buy a TDS meter and measure your tap water, your filtered water, and a few bottled waters you have at home. Brew the same recipe with each. The differences will surprise you, and you will quickly identify which water source is worth using for daily brewing.
General Hardness (GH): The Extraction Engine
GH, or general hardness, measures the concentration of calcium and magnesium ions in your water. These two minerals are the workhorses of extraction. They bond chemically with flavor compounds in coffee, particularly the organic acids and aromatics that give pour-overs their clarity and sweetness.
In most cases, magnesium is the more flavor-active of the two. It tends to enhance brightness and lift fruit notes, which is why many DIY water recipes for coffee, including the ones popularized by writers like Hoffmann and the Barista Hustle team, lean heavily on magnesium sulfate.
Calcium contributes body and a sense of weight in the cup, but it also forms scale inside kettles and espresso machines. There is a tradeoff between flavor extraction and equipment longevity, and most coffee-focused water recipes use less calcium than typical municipal water.
A reasonable target for GH in pour-over water sits somewhere in the range of 50 to 150 mg/L expressed as CaCO3, though preferences vary widely. Brewers chasing the bright, tea-like extractions associated with [Tetsu Kasuya](https://cup-timer.com/en/barista/tetsu-kasuya) style recipes often prefer the lower end of that range. Those pursuing the heavier, more syrupy profiles described by Scott Rao sometimes push higher.
Alkalinity (KH): The Buffer
KH measures alkalinity, primarily bicarbonate ions. Its role is fundamentally different from GH. Where calcium and magnesium grab onto flavor compounds, bicarbonate buffers the brew, neutralizing the natural acidity of coffee.
This is a double-edged sword. Some buffering smooths out harsh, sour, under-extracted notes and makes the cup feel more balanced. Too much buffering, however, strips the coffee of its lively acidity and leaves a flat, lifeless drink. This is why high-alkalinity tap water often makes even great beans taste boring.
A common target range is roughly 40 to 75 mg/L as CaCO3, lower than typical municipal supplies in many regions. If your tap water tastes "soft" or comes from a well that runs through limestone, you almost certainly have more KH than is ideal for pour-over.
Actionable Tip
If you do not want to mix custom water from scratch, try cutting your tap water with distilled or reverse-osmosis water at a 50:50 ratio. This single change often dramatically lowers both TDS and KH while keeping enough mineral content for proper extraction. Brew side by side with your normal water and judge for yourself.
Putting It Together for Pour-Over
The three numbers interact. High TDS with low GH and high KH means lots of buffering and little extraction power, a recipe for muted cups. Low TDS with balanced GH and KH gives clean, bright extractions but can tip toward harshness if your beans are roasted dark.
For most home setups using an April, V60, or Chemex with light to medium roasts, aim for something in this neighborhood:
- TDS: roughly 100 to 200 ppm
- GH: roughly 50 to 100 mg/L as CaCO3, magnesium-leaning if you are mixing
- KH: roughly 40 to 75 mg/L as CaCO3
Hit those windows and most beans will brew within a recognizable, enjoyable range. From there, the usual variables, grind size, ratio, bloom duration, agitation, take over and drive the cup-by-cup differences you taste.
Water is the silent partner in every pour-over. Once you start paying attention to it, the rest of your dialing-in process becomes faster, more predictable, and far more rewarding.