Water quality is usually the last thing we talk about to make a great espresso.
People obsess over beans, grinders, pressure, and tamping, but few stop to consider what’s in the water. Espresso is over 90% water. Whatever minerals, gases, or chemicals are in that water are going straight into your cup and your machine.
This matters more than most people realize. Not just for taste, but for crema, brewing consistency, and the long-term health of your espresso machine. In this post, we’re digging into what water quality really means for espresso, how it affects the final cup, and what kind of filtration you actually need.
Why Water Composition Changes Espresso
A 2010 study by Navarini and Rivetti tested how different waters impacted espresso. It found that even subtle changes in water chemistry can alter extraction time, crema formation, and taste. Their results confirmed that water isn’t neutral. It actively reacts with the coffee bed and affects both flavor and physical properties.
The most important water components are:
- Hardness minerals (calcium and magnesium)
- Bicarbonate content
- Sodium (from softened water)
- Chlorine (from municipal disinfection)
- Dissolved CO₂
- pH and total alkalinity
All of these interact with ground coffee, especially during espresso brewing where water is forced through under pressure at 90-94 °C.
The mineral content doesn’t just affect the taste. It changes how fast water moves through the puck, how much coffee solids are extracted, and how the crema forms and behaves.
The Impact of Hardness and Bicarbonates
Hardness in water comes mainly from calcium and magnesium. They help bind with organic acids and oils in coffee, improving flavor and mouthfeel. But they also contribute to limescale, which builds up inside the coffee machine group head (the metal assembly at the front of the machine that delivers hot, pressurized water into the coffee puck).
Bicarbonates (HCO₃⁻), on the other hand, are a bit more complicated. They act as a buffer, neutralizing the acids in coffee. This can be helpful in small amounts, but too much flattens the coffee’s acidity and makes it taste dull or even bitter.
High bicarbonate water also affects crema: it may boost the initial foam but leads to a weak, unstable texture that collapses quickly.
Espresso brewed with high-bicarbonate water can give higher foam volume but also large bubbles and poor foam stability. Espresso made with low-bicarbonate water will have less foam, but is generally finer and longer-lasting.
When we talk about bicarbonate levels in water (usually measured as HCO₃⁻ in mg/L or converted to alkalinity as calcium carbonate (CaCO₃)). The terms “low,” “medium,” and “high” refer to the buffering capacity of the water (i.e., how much it can neutralize acids).
Bicarbonate Level Categories
| Category | Bicarbonate (HCO₃⁻) | Alkalinity (as CaCO₃) | Effect on Espresso |
|---|---|---|---|
| Low | 0–50 mg/L | 0–40 mg/L | Bright, acidic espresso with better crema stability; can be too sour if very low. |
| Medium | 50–150 mg/L | 40–100 mg/L | Balanced acidity and body; good flavor clarity and crema. This is the target range. |
| High | 150–300+ mg/L | 100–200+ mg/L | Dull, flat, or bitter espresso; unstable crema; can cause fast scaling in machines. |
Note: The Specialty Coffee Association (SCA) recommends alkalinity in the range of 40–60 mg/L as CaCO₃, which usually corresponds to ~50–75 mg/L of HCO₃⁻.
The Problem with Sodium-Softened Water
Many households use sodium-based water softeners to reduce scale. While this can protect plumbing, it’s not ideal for coffee.
Sodium-softened water causes brewing time to increase by as much as 80% (Navarini and Rivetti 2010).
Why? When calcium and magnesium are replaced by sodium, water interacts differently with the coffee bed. Sodium ions promote more swelling of the coffee grounds, especially the insoluble fibers like cellulose and mannan, which reduces porosity. The result is a slower flow and sometimes uneven extraction. This doesn’t just change timing, it can cause your espresso to taste over-extracted or bitter.
If you’ve ever noticed that espresso from softened water feels over-brewed, now you know why.
Crema: Not Just a Visual Detail
Espresso crema is more than just foam on top. It’s considered a marker of a good shot.
It forms when CO₂ gas trapped in roasted coffee is released under pressure and emulsified into the liquid. Water chemistry affects how well this gas is released and how stable the bubbles are.
Researchers have measured foam volume from espresso made with various waters.
Espresso made with pure water (like Milli-Q ultra-filtered water) creates the least foam, while high-bicarbonate water (like hard bottled mineral water) creates the most.
But here’s the catch: high-bicarbonate water also made crema that collapsed within 30 seconds.
In contrast, crema from low-mineral water held its structure for several minutes and had a finer texture.
It turns out, a “big” crema isn’t always a better crema.
Do You Need a Water Filter to Make Good Coffee?
If you’re using tap water in your espresso machine, the answer is almost always yes, but usually only a basic one. Municipal tap water is treated with chlorine or chloramine to disinfect it, and both add harsh chemical flavors to coffee.
Even if your water is safe to drink, it may not be ideal for brewing.
Let’s break down your options:
| Filter Type | What It Removes | Espresso Friendly? |
|---|---|---|
| Carbon filters | Chlorine, taste, odor | Essential |
| Ion-exchange softeners | Calcium, magnesium (replaced with sodium) | Not ideal for taste |
| RO systems | Almost all dissolved solids | With remineralization |
| Espresso-specific filters | Scale + balanced minerals | Best option |
Using reverse osmosis (RO) without remineralizing the water afterward is also a problem. It can make the water too aggressive and extract harsh flavors, while also being corrosive to your machine’s internals.
If you use RO, choose a system that reintroduces magnesium and small amounts of calcium for flavor and safety.
What the “Best” Water Looks Like
There’s no universal standard, but the Specialty Coffee Association (SCA) and most espresso machine manufacturers recommend water in the following ranges:
| Parameter | Target Range |
|---|---|
| Hardness | 70–100 mg/L (as CaCO₃) |
| Alkalinity | 40–60 mg/L (as CaCO₃) |
| TDS (Total Dissolved Solids) | 100–200 mg/L |
| pH | 6.5–7.5 |
| Chlorine | 0 mg/L |
These levels help balance flavor extraction with machine maintenance. Outside these ranges, you risk flavor issues, poor crema, or scale build-up.
Why All This Matters
“Even bad coffee is better than no coffee at all.” – David Lynch
However, if you’re serious about your espresso and care about taste, the right water can make a big difference.
Good water quality improves flavor clarity, consistency, and crema. It also reduces wear on your machine, especially in areas with hard water.
Reference:
Navarini, L. and Rivetti, D., 2010. Water quality for Espresso coffee. Food chemistry, 122(2), pp.424-428. <https://doi.org/10.1016/j.foodchem.2009.04.019>