Water Chemistry
How TDS, calcium, magnesium, and bicarbonate affect extraction and flavor.
Water makes up ~98% of your cup. Its mineral composition affects extraction efficiency, flavor, and equipment longevity. The SCA recommends specific ranges for each mineral.
SCA Water Quality Guidelines
| Parameter | SCA Target | Acceptable Range |
|---|---|---|
| Total Dissolved Solids (TDS) | 150 mg/L | 75–250 mg/L |
| Calcium Hardness | 68 mg/L | 17–85 mg/L |
| Total Alkalinity | 40 mg/L | at target |
| pH | 7.0 | 6.5–7.5 |
| Sodium | 10 mg/L | <30 mg/L |
| Chlorine | 0 mg/L | 0 mg/L |
Tap water quality varies enormously by city. Always check your local water report or use a TDS meter before assuming your water is suitable.
The Key Minerals
Calcium & Magnesium (Hardness)
These minerals are the primary extractors — they bind to flavor compounds in coffee and pull them into solution.
- More Ca/Mg → stronger extraction, more body, can increase bitterness
- Too soft → flat, underextracted, lacking complexity
- Too hard → harsh, scale buildup in machines
Magnesium is more selective — it preferentially extracts sweeter, more desirable flavors. Some specialty coffee water recipes optimize for magnesium over calcium.
Bicarbonate (Alkalinity)
Bicarbonate acts as a buffer — it neutralizes acid in your cup.
- High alkalinity → mutes acidity, flat cup, can taste chalky
- Low alkalinity → bright, acidic cup, flavor is more transparent
- Zero alkalinity → can make acidic coffees uncomfortably sharp
Target ~40–70 mg/L for most filter coffee.
Sodium
Small amounts of sodium round out flavor and can enhance sweetness. Above 30 mg/L it starts to taste salty.
Practical Water Options
| Option | Pros | Cons |
|---|---|---|
| Filtered tap (Brita, etc.) | Convenient | Inconsistent, may not remove enough |
| Third Wave Water | Purpose-made, consistent | Costs money, requires distilled base |
| Custom mineral mix | Maximum control | Time-consuming, needs distilled water |
| Bottled still water | Easy, consistent | Environmental impact |
Brew Calculator
Use this calculator to find how much water you need for any dose and ratio.
Brew Calculator
Soft vs. Hard Water Adjustments
If your water is too hard (>200 mg/L TDS):
- Use a 50/50 blend of tap and distilled
- Install a water softener or RO filter + remineralize
If your water is too soft (<75 mg/L TDS):
- Add Third Wave Water mineral packets to distilled
- Or use: 1.5g Epsom salt + 1g baking soda per 1L distilled water (approximation)
A cheap TDS meter (€10–20) is one of the highest-ROI purchases in home coffee. Measure your tap water first — you might already be in range.