Coffee in a cup is 98-99% water. If the water is bad, nothing else matters — perfect grind, fresh coffee, expensive machine, but if the water isn't right, the taste will be ruined.
TDS — the most important parameter
TDS (Total Dissolved Solids) = how much mineralization the water has. Measured in ppm (parts per million).
For coffee, the ideal range:
- 50-150 ppm for filter coffee (V60, Chemex, AeroPress)
- 75-150 ppm for espresso
Below 50 ppm — water too "empty." The coffee tastes bland and under-extracted, lacking complexity.
Above 200 ppm — water too mineralized. The coffee tastes flat, bitter, with a metallic taste. Plus, the machine quickly builds up scale deposits.
Store-bought water (in Romania)
- Aqua Carpatica — ~700 ppm TDS. Too mineralized for coffee. Leaves the coffee flat and quickly causes scale deposits on the machine.
- Dorna — ~300 ppm. Still too much, but closer.
- Bilbor — ~150 ppm. Nearly ideal for filter coffee.
- Borsec (still, NOT sparkling) — ~250 ppm. At the upper limit.
- Tap water in Bucharest — ~250-400 ppm, plus chlorine. Not suitable directly.
Practical solutions
For a single coffee at home: Buy bottled still water. Bilbor or Borsec still. Use directly.
For regular consumption (3+ coffees/day): Faucet filter or pitcher with filter.
- Brita Standard / Maxtra+ (~150 RON pitcher + 25 RON/filter) — reduces chlorine and some mineralization. Functional for filter coffee.
- BWT Magnesium (~200 RON) — adds magnesium for better extraction. More recommended by specialty coffee experts.
For a coffee shop or serious home espresso: Professional system.
- BWT bestmax or Brita Purity (~800-2,000 RON) — installed on the water line. Filters 30-50% of mineralization, retains chlorine, regulates pH.
- Reverse osmosis system + remineralization (~1,500-3,000 RON) — the best option. Water becomes pure (~0 ppm) and you re-mineralize it controllably to 100 ppm.
Demineralized water — DO NOT use
Distilled or demineralized water (from stores as "Water for batteries") is 0 ppm. It does not work for coffee — minerals are missing, extraction is wrong, the taste is "empty."
Secondary parameters (advanced)
GH (General Hardness) — how much calcium and magnesium the water has. Ideal: 50-100 ppm. SCA specification: 68 ppm calcium carbonate.
KH (Carbonate Hardness) — how much bicarbonate. Ideal: 40-70 ppm. Too high KH causes scale deposits in the boiler.
pH — ideal 6.5-7.5 (neutral). Coffee brews best with slightly alkaline water.
How to test water
- TDS meter (~50-100 RON on Amazon) — tests TDS in 5 seconds.
- pH strips (~30 RON) — tests pH.
- Complete GH/KH kit (~80-150 RON) — for advanced users.
The perfect water recipe in specialty coffee
Specialty professionals use "water recipes" — they mix magnesium sulfate + sodium bicarbonate in demineralized water to obtain the exact composition. The classic recipe (Maxwell Colonna-Dashwood):
- 3.5g magnesium sulfate heptahydrate
- 2.8g sodium bicarbonate
- 1 liter distilled water
- = water with an ideal profile for specialty coffee
For most people, it's too much hassle. Good bottled water or a pitcher filter is sufficient.
Conclusion
Invest in water. It's the cheapest upgrade you can make to your setup. 50 RON in a Brita filter = the same change in the cup as 500 RON in a new grinder.
For complete brewing recipes, see our calculator.