tags: [] - coffee/brewing - coffee/brewing/water aliases: - Measuring water TDS - EC measurement water - Total dissolved solids testing

TDS Measurement¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Measuring water TDS, EC measurement water, Total dissolved solids testing Related: Water in Coffee MOC | Total Dissolved Solids | TDS Meters | Water Standards | Measurement Tools Status: ✅ Complete

Overview¶

Water TDS (Total Dissolved Solids) is measured by one of two methods: electrical conductivity (EC) measurement using a conductivity meter, which provides a rapid estimate of total ion concentration, or gravimetric analysis (evaporation to dryness), which is the definitive laboratory method. In coffee water management, EC meters are the practical tool of choice — inexpensive, fast, and sufficiently accurate for water recipe development and monitoring. The relationship between EC and TDS requires a conversion factor that varies depending on the ion composition of the specific water.

Electrical Conductivity (EC) Method¶

Dissolved ions conduct electricity; the more ions present, the higher the conductivity. An EC meter measures the ability of the water to conduct electrical current between two electrodes, expressed in microsiemens per centimetre (µS/cm) or millisiemens per centimetre (mS/cm).

TDS (mg/L) ≈ EC (µS/cm) × conversion factor

Common conversion factors: - 0.5 (widely used for natural water and water recipes with mixed mineral composition) - 0.64 (used by some instruments for sodium chloride–calibrated measurements) - 0.67 (used for water rich in bicarbonate/carbonate) - 0.7 (some European water standards)

The conversion factor is an approximation because different ions conduct electricity with different efficiency: - Sodium, potassium, chloride, and bicarbonate are highly conductive per unit mass - Calcium and magnesium are somewhat less conductive per unit mass

For coffee water work, the 0.5 factor is the most common and produces estimates that are sufficiently accurate for recipe work and monitoring purposes. The SCA target TDS of 150 mg/L corresponds to approximately 250–300 µS/cm EC.

Gravimetric Analysis¶

The reference method for TDS measurement: 1. Filter a known volume of water through a 0.45 µm membrane filter to remove suspended solids 2. Evaporate the filtered sample to dryness at 180°C in a pre-weighed evaporating dish 3. Cool to room temperature in a desiccator, then weigh the residue 4. TDS (mg/L) = (residue mass in mg) ÷ (sample volume in litres)

This method is slow, requires laboratory equipment, and is not practical for routine café use — but it is the definitive measurement against which EC-based methods are calibrated.

EC Meters for Coffee Water¶

Pocket EC/TDS meters are the standard tool for routine coffee water monitoring: - Design: Handheld probe with two or four electrodes; temperature sensor; digital display - Reading: Display in µS/cm (conductivity) or direct TDS estimate in mg/L (using internal conversion factor) - Calibration: With certified conductivity standard solution (typically 1413 µS/cm KCl standard) - Accuracy: ±2–5% of reading for quality instruments - Common brands: Hanna Instruments (HI 9813-6, HI 98301), Milwaukee (MW302), Apera (PC60)

See TDS Meters for detailed instrument selection guidance.

What EC Does Not Measure¶

EC meters measure only ionic dissolved substances — not non-ionic dissolved organics, dissolved gases (CO₂, O₂), or colloidal material. This is rarely a practical concern for clean municipal or well water used for coffee, but: - Distilled water with dissolved CO₂ from the atmosphere shows low but non-zero EC (CO₂ forms carbonic acid, which ionises slightly) - Water with organic contamination may have low EC but significant non-ionic dissolved material

Interpreting TDS Readings¶

EC (µS/cm)	Estimated TDS (×0.5)	Assessment
< 50	< 25 mg/L	Very low (RO permeate or distilled); requires remineralisation
100–200	50–100 mg/L	Low-moderate; may produce thin body
200–350	100–175 mg/L	SCA target zone (75–250 mg/L TDS)
350–500	175–250 mg/L	SCA acceptable upper range
> 500	> 250 mg/L	Elevated; check alkalinity and hardness
> 1000	> 500 mg/L	Very high; unsuitable for coffee without treatment

Key Facts¶

Water TDS is measured by EC (rapid, practical) or gravimetric analysis (laboratory reference method)
EC (µS/cm) × 0.5 ≈ TDS (mg/L) for typical mixed-mineral water; exact factor varies by ion composition
SCA TDS target: 150 mg/L ≈ 250–300 µS/cm EC
EC meters require calibration with certified conductivity standard; accuracy ±2–5%
EC measures ionic content only; non-ionic dissolved organics are not detected

References¶

Changelog¶

Date	Change
2026-04-28	Note created

This article is part of All-About-Coffee.com - The comprehensive coffee knowledgebase.