🕒 Estimated read time: 4 minutes
If you’ve been chasing cleaner, sweeter brews, water chemistry for coffee is the quiet variable you can actually control.
And if your cups are inconsistent day to day, it’s worth checking the basics first - start with grind size in our How to Grind Coffee Beans guide, then come back to water.
The Speciality Coffee Association publishes a brewing‑water standard with target ranges for minerals, pH, and other parameters, and it’s a helpful baseline for home brewers.
You don’t need a lab to get value from it. Know what the numbers mean, then compare your water report to the standard.
The three numbers that actually matter
TDS (total dissolved solids) is the sum of all substances dissolved in water. The USGS definition of TDS lists common ions like calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica.
Water hardness is essentially the amount of dissolved calcium and magnesium, as explained in the USGS Water Science School: Hardness of Water.
Alkalinity is the buffering capacity of water and depends on dissolved bicarbonates, carbonates, and hydroxides (see USGS: Alkalinity and Water).
USGS classifies hardness levels as soft (0 to 60 mg/L as CaCO3), moderately hard (61 to 120), hard (121 to 180), and very hard (greater than 180) in its water hardness FAQ.
☕ Brewing Tip
Because alkalinity is the buffering capacity of water, higher alkalinity means the water resists pH change more, so it’s a useful, quick indicator of how strongly water will neutralise acids.
What the SCA brewing‑water standard recommends
The brewing‑water standard lists target values and acceptable ranges for key parameters used in brewing.
- TDS: target 150 mg/L, acceptable range 75 to 250 mg/L.
- Calcium hardness: target 68 mg/L (4 grains), acceptable range 17 to 85 mg/L.
- Total alkalinity: target 40 mg/L, acceptable near 40 mg/L.
- pH: target 7.0, acceptable range 6.5 to 7.5.
- Sodium: target 10 mg/L.
- Total chlorine: target 0 mg/L.
☕ Brewing Tip
If your numbers sit inside the SCA acceptable ranges, you’re within the industry’s baseline; use the target values as a practical starting point for dialling in.
If you brew pour‑over, pairing those targets with a simple method helps you feel the difference quickly. Our V60 Brewing Guide is a solid place to start.
Red flags that show up in real water reports
Very hard water is defined as greater than 180 mg/L as CaCO3, and hard water can form scale in equipment when heated (see the USGS water hardness FAQ).
TDS above 250 mg/L or below 75 mg/L sits outside the SCA acceptable range, per the SCAA Standard.
The SCA target for total chlorine is 0 mg/L, so any reported chlorine is outside the target (see the SCAA Standard).
☕ Brewing Tip
If your hardness category is “very hard,” plan for scale management because hard water is associated with scale formation in equipment.
How to use your water report (simple checklist)
- If you’re on municipal water, grab your annual consumer confidence report; suppliers are required to send these, and they include measured levels for key parameters (see the USGS water hardness FAQ).
- Locate TDS, hardness (as CaCO3), alkalinity, pH, chlorine, and sodium. These are the parameters called out in the SCAA Standard.
- Compare your TDS to the SCA range of 75 to 250 mg/L (target 150).
- Compare calcium hardness to 17 to 85 mg/L and note your hardness category (soft, moderately hard, hard, very hard).
- Check total alkalinity near 40 mg/L and pH between 6.5 and 7.5.
☕ Brewing Tip
Those reports already list contaminant levels and related measurements, so you can use them as a baseline before buying any test gear.
If you brew cafetière, temperature matters as much as minerals — see The Ideal Water Temperature for Your Cafetière for a quick sanity‑check.
Quick summary
- TDS is the total dissolved solids in water, including common ions like calcium, magnesium, sodium, and bicarbonate
- Hardness is primarily the amount of dissolved calcium and magnesium, with USGS hardness categories from soft to very hard
- Alkalinity is the buffering capacity of water, tied to bicarbonates, carbonates, and hydroxides.
- The SCA standard targets TDS 150 mg/L (acceptable 75 to 250), calcium hardness 68 mg/L (17 to 85), alkalinity 40 mg/L, pH 6.5 to 7.5, chlorine 0 mg/L, and sodium 10 mg/L.
FAQs
What does TDS actually measure?
It’s the sum of all dissolved substances in water, including a mix of common ions like calcium, magnesium, sodium, and bicarbonate.
Is hardness the same as alkalinity?
No. Hardness is the amount of dissolved calcium and magnesium, while alkalinity is the buffering capacity of water driven by bicarbonates, carbonates, and hydroxides.
What are the SCA target numbers I should aim for?
The SCA standard targets TDS 150 mg/L, calcium hardness 68 mg/L, total alkalinity 40 mg/L, pH 7.0, sodium 10 mg/L, and total chlorine 0 mg/L, with acceptable ranges noted above.