Coffee is approximately 98–99% water. This should make water the most discussed variable in home coffee brewing. Instead, it's almost entirely ignored. Here's why water chemistry matters — and what you can practically do about it.
What's in Your Water
Tap water varies dramatically by location. The key factors that affect coffee brewing are:
- Hardness (calcium and magnesium): Hard water contains more dissolved minerals. Magnesium in particular is excellent for coffee — it enhances extraction of aromatic compounds. Calcium helps too, but less so.
- Carbonate hardness (alkalinity / bicarbonates): High alkalinity neutralises the acids in coffee, producing a flat, dull cup. This is the most common water problem for coffee brewing.
- Chlorine and chloramines: Added to municipal water for safety. Both add off-flavours to coffee.
- TDS (Total Dissolved Solids): A measure of everything dissolved in the water. Very high TDS water (>300 ppm) can produce flat, dull coffee. Very low TDS water (<50 ppm) can produce thin, astringent coffee.
The Ideal Brewing Water
The Specialty Coffee Association recommends water with 75–250 ppm TDS, 50–175 ppm hardness, minimal chlorine, and pH of 6.5–7.5. This sounds technical but in practice simply means: moderately mineral water, not too hard, not too soft, with no taste of chlorine.
What to Do With Your Tap Water
You have several options, in increasing order of commitment:
- Filtered water: A basic Brita or similar filter removes chlorine and reduces some minerals. Significant improvement over unfiltered tap water in most regions. Easy and cheap.
- Bottled still water: Check the label for mineral content. Volvic (130 ppm TDS, low bicarbonates) is widely recommended for coffee. More expensive but simple.
- Third Wave Water minerals: Mineral packages you add to distilled water to create "ideal" brewing water. Precise but involves buying distilled water and mixing packets. Worth it for serious home brewers.
Very Soft Water
Soft water (low mineral content) is less common as a problem but does occur. If your water TDS is below 50 ppm (common in some Nordic countries and parts of the UK with naturally soft water), coffee can taste thin and lack body. Adding small amounts of mineral mix or using slightly harder bottled water helps.