TDS and Mineral Content
Total Dissolved Solids (TDS) is the total mass of dissolved substances in water, usually expressed in parts per million (ppm) or milligrams per litre (mg/L — the same number). For brewing water, that means everything dissolved before the coffee touches it: calcium, magnesium, bicarbonate, sodium, chloride, and trace minerals. A higher TDS means more mineral content available to pull flavor from the bed; a near-zero TDS — distilled or fresh reverse-osmosis water — means almost nothing is there to extract with, and the cup suffers. This note is about the mineral content of your brewing water, the front end of the whole water story.
Water TDS is the mineral content of the water before brewing (this note). Brew TDS is the strength of the finished coffee — the percentage of dissolved coffee solids a refractometer reads, typically ~1.2–1.5%, covered in Total Dissolved Solids (TDS) and Extraction Yield and Strength. Same acronym, opposite ends of the brew.
#Measuring It 🔍
The cheap, common tool is a TDS meter (EC/conductivity pen). It does not actually count dissolved solids — it measures electrical conductivity and multiplies by a conversion factor to estimate ppm. That makes it a fast, rough gauge of "how mineral" your water is, but it is blind to the GH/KH split that actually matters for flavor: two waters can read the same TDS yet brew completely differently if one is mostly extracting magnesium and the other mostly buffering bicarbonate. For that distinction, use GH/KH drop tests, not the pen — see Water Chemistry — Hardness and Alkalinity.
#What a Good Number Looks Like
| Water TDS (ppm) | Character | Verdict for brewing |
|---|---|---|
| 0–30 | Distilled / fresh RO | Too low — extracts poorly, hollow cup |
| 50–100 | Lightly to moderately mineral | Sweet spot for most pour over |
| ~150 | The SCA reference point | Solid target; see The SCA Water Standard |
| 175–250 | Hard | Often over-buffered; mutes acidity |
| 250+ | Very hard | Flat cups and scale on the kettle |
The widely used reference target is around 150 ppm, with a workable band of roughly 75–175 ppm. But TDS is only a headline figure: what makes up that number — the balance of extracting minerals versus buffering bicarbonate — decides the cup far more than the total.
#Why Total Alone Isn't Enough 🎯
Because a TDS pen cannot see composition, chasing a target ppm without knowing your GH and KH is like setting a brew ratio without weighing the coffee. A 150 ppm water that is nearly all bicarbonate will brew flat and chalky; a 150 ppm water weighted toward magnesium will brew bright and extractive. Use TDS as a quick sanity check and a way to confirm a built-water recipe landed where you intended, then trust GH/KH for the flavor decisions. The interaction of mineral content with solubility and temperature is what ultimately sets your yield.
#Continue Reading
- Water Chemistry — Hardness and Alkalinity — the composition a TDS pen can't see
- The SCA Water Standard — where the ~150 ppm target comes from
- Total Dissolved Solids (TDS) — the other TDS: strength of the finished cup
- Building Water — Recipes and Remineralization — hit a target ppm on purpose
- Water for Coffee — back to the water hub