Coffee is about 98% water. The quality of that water — its mineral content, hardness, and any off-flavors — has a direct and measurable impact on the taste of the final cup. This is one of the more practical, low-effort improvements you can make to your home brewing.
What’s in Tap Water
Tap water varies dramatically by location. Some cities have soft, relatively neutral water that’s fine for coffee. Others have hard water with high mineral content (primarily calcium and magnesium), which affects extraction. Some areas have chlorine or chloramines added for water treatment, which produce off-flavors in coffee.
The SCA’s water quality standards for brewing specify a target total dissolved solids (TDS) of 150ppm, with acceptable range of 75–250ppm. Most municipal tap water falls somewhere in this range, but consistency varies.
The Chlorine Problem
Chlorine in tap water is one of the most detectable off-flavors in coffee. If your coffee has a slightly chemical or flat taste that doesn’t match the beans’ quality, chlorine may be the culprit.
Simple carbon block filters (like Brita pitcher filters or faucet-mounted filters) effectively remove chlorine and chloramines. This is the easiest improvement you can make and costs almost nothing per cup.
Mineral Content: Not All Filtering Is Equal
This is where it gets more nuanced. Minerals — particularly magnesium and calcium — help extract coffee compounds. Completely pure or distilled water, with no mineral content, actually produces flat, under-extracted coffee because there’s nothing to help pull compounds from the grounds.
The goal isn’t mineral-free water; it’s water with the right amount of the right minerals. A Brita filter or similar carbon filter removes chlorine without stripping minerals, which is usually optimal for coffee.
Reverse osmosis systems remove almost everything, which is too aggressive. If you have RO water, you’d need to add minerals back (coffee-specific mineral packets exist for this).
The Practical Recommendation
Use filtered water (carbon filter, Brita type). If your tap water tastes fine on its own, it’s probably fine for coffee. If it has a noticeable chlorine smell or off-taste, filtering will improve your coffee noticeably. Bottled still water is a good experiment — if your coffee tastes significantly better with bottled water, the filter investment is worth it.
