tags: [] - coffee/brewing - coffee/brewing/water aliases: - TDS water - Total dissolved solids coffee - Water TDS

Total Dissolved Solids¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: TDS water, Total dissolved solids coffee, Water TDS Related: Water in Coffee MOC | TDS Measurement | Hardness | Alkalinity | Water Standards Status: ✅ Complete

Overview¶

Total Dissolved Solids (TDS) is a measure of the total mass of all dissolved mineral salts, ions, and compounds present in a water sample, typically expressed in milligrams per litre (mg/L) or parts per million (ppm). In the context of coffee water, TDS reflects the overall mineral content of the source water — the combined concentration of calcium, magnesium, sodium, potassium, bicarbonate, chloride, sulfate, and other dissolved species. TDS is an important but incomplete indicator of water quality for coffee: it quantifies how much is dissolved in the water but does not distinguish between different mineral types, which have very different effects on coffee extraction and flavour.

TDS in the Context of Coffee Water vs. Brewed Coffee¶

The term TDS is used in two distinct contexts in coffee:

Water TDS (source water): The concentration of dissolved minerals in the brewing water before coffee contact — the subject of this article. Measured in mg/L. SCA target: 150 mg/L.
Beverage TDS (brewed coffee): The concentration of dissolved coffee compounds in the finished cup — a measure of brew strength. Measured by refractometer in Brix, converted to % TDS (typically 1.15–1.45% for filter coffee). This is a different concept from water TDS, though the same abbreviation is used.

Effect of Water TDS on Coffee Extraction¶

Very low TDS water (below ~50 mg/L): - Distilled water or water after reverse osmosis without remineralisation - Aggressive extraction: without dissolved minerals, the water has a higher chemical potential difference relative to the concentrated coffee solution, driving more aggressive extraction - Results in flat, thin, or harsh cups — lacks the ionic interactions (particularly magnesium and calcium binding to flavour compounds) that contribute to full flavour development - Corrosive to metal equipment components

Low to moderate TDS (75–150 mg/L): - Generally good extraction dynamics - Coffee acidity and aromatics are expressed clearly - Low scale risk - Some mineral character contribution; may lack body if calcium and magnesium are very low

Moderate TDS (150–250 mg/L): - SCA sweet spot; good balance of mineral contribution and extraction dynamics - Body and mouthfeel contributions from calcium and magnesium - Manageable scale risk depending on calcium hardness and temperature

High TDS (above 250–300 mg/L): - Reduced extraction rate: the small concentration gradient between high-mineral water and coffee solution slows diffusion of coffee solubles - Water may already contain significant flavour-relevant minerals that compete with or mask coffee compounds - High scale risk (particularly if calcium carbonate hardness is elevated) - Cup may taste flat, mineralised, or lacking clarity

TDS Measurement¶

Water TDS is measured using: - Electrical conductivity (EC) meters: Measure the water's ability to conduct electricity, which is proportional to dissolved ion concentration; EC is converted to estimated TDS using a conversion factor (typically 0.5–0.7 × EC in µS/cm = TDS in mg/L). Inexpensive and rapid but measures ions only, not non-ionic dissolved substances - Gravimetric analysis: Evaporate a known volume of water at 180°C and weigh the residue; the most accurate method but requires laboratory equipment

See TDS Measurement and TDS Meters.

TDS vs. Hardness and Alkalinity¶

TDS is a summary measure; its composition matters more than the total. Two water samples with identical TDS can produce very different coffee if their mineral composition differs:

Water A: 150 mg/L TDS, primarily bicarbonate → flat, low-acid coffee
Water B: 150 mg/L TDS, primarily calcium/magnesium sulfate and chloride → bright, complex coffee

For this reason, full water analysis — measuring individual ion concentrations — is more informative than TDS alone for diagnosing water quality problems or designing water recipes.

Key Facts¶

Water TDS (source water) = total mass of dissolved minerals in mg/L; SCA target is 150 mg/L (range 75–250 mg/L)
TDS indicates total mineral content but not composition — two waters at the same TDS can produce very different coffee depending on which minerals are present
Very low TDS water (distilled/RO without remineralisation) produces aggressive but flat extraction; very high TDS reduces extraction efficiency and increases scale risk
TDS is measured by electrical conductivity meter (EC × conversion factor) or laboratory gravimetric analysis
"Brewed coffee TDS" (beverage strength measured by refractometer) is a different concept from "water TDS" — both use the same abbreviation in coffee terminology

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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