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Water, TDS & Extraction: The Science of What's Really in Your Cup
01 / GENFRESH™ FIELD NOTES — FROM THE ROASTERY
Water, TDS & Extraction
Coffee is ninety-eight percent water. Yet most brewing advice focuses entirely on the other two percent — the beans, the grind, the roast. This is the deep dive on the part nobody talks about.
Water makes up 98% of what's in your cup — the medium every flavor compound has to pass through.
02 / WHY WATER IS THE VARIABLE EVERYONE SKIPS
The Most Overlooked Ingredient in Coffee
A finished cup of brewed coffee is roughly 98% water by weight. That single fact reframes almost everything about brewing: the beans supply flavor potential, but water is the medium that actually pulls that potential into the cup — or fails to. Two identical coffees, brewed identically, can taste meaningfully different depending on nothing more than what came out of the tap.
This isn't a marginal effect. Water chemistry determines how efficiently flavor compounds — acids, sugars, aromatic oils, and hundreds of other soluble molecules formed during roasting — transfer out of the ground coffee and into solution. Get the water wrong, and no amount of dialing in grind size, ratio, or brew time will fully compensate.
Curious how your own water measures up?
Jump to the home test guide below — or watch the full breakdown first.
TRY THE HOME TEST03 / THE CORE CONCEPT
What TDS Actually Measures
TDS stands for Total Dissolved Solids — the combined concentration of everything dissolved in a liquid, measured in parts per million (ppm) or milligrams per liter (mg/L), which are functionally the same unit. In brewing water, TDS is dominated by calcium, magnesium, bicarbonate, sodium, and trace sulfates and chlorides. In a finished brewed coffee, TDS instead measures the concentration of dissolved coffee solids — the actual "strength" of the cup.
These are two different measurements of the same underlying idea: how much material is dissolved in the water. Before brewing, TDS tells you what your water is starting with — how many "open seats" are already occupied by minerals versus available to help pull flavor compounds out of the coffee bed. After brewing, TDS combined with brew ratio tells you the extraction yield — the percentage of the coffee's soluble mass that actually made it into the cup.
Two TDS measurements, two purposes:
• Water TDS (before brewing) — mineral content of the water itself, target ~150 ppm
• Brew TDS (after brewing) — dissolved coffee solids in the finished cup, target 1.15%–1.35% for filter coffee per SCA guidelines
The Golden Cup extraction chart below illustrates the second measurement — how brew strength (TDS) and extraction percentage interact to define the zone the SCA considers balanced, versus under- or over-extracted:
The SCA Golden Cup zone: balanced extraction (18–22%) at a brew strength of 1.15%–1.35% TDS for filter coffee.[2] Water chemistry is the primary lever controlling how efficiently extraction happens within this window.
A refractometer reading in progress — the same tool used to measure extraction yield in the video below.
04 / DEEP CHEMISTRY
The Minerals That Actually Matter
Not all dissolved solids behave the same way in coffee. Below is every ion with a documented, meaningful effect on extraction or flavor — what it does, and why.
Calcium (Ca²⁺)
The dominant mineral in most municipal hard water. Calcium ions bind to certain flavor-active compounds — particularly organic acids and heavier aromatic molecules — and pull them into solution during extraction, a process central to how flavor actually leaves the coffee grounds.[3] Calcium is generally associated with body and perceived sweetness in the finished cup. Combined with bicarbonate and heat, calcium also forms calcium carbonate — limescale — which is the same chemistry responsible for scale buildup in kettles and espresso machines.
Magnesium (Mg²⁺)
Chemically similar to calcium but binds preferentially to different flavor compounds — magnesium is more strongly associated with extracting aromatic, fruit-forward, and brighter acidic notes.[3] Water recipes built for specialty light roasts often lean on magnesium specifically because of this brightness effect.[4] Along with calcium, magnesium makes up what water chemists call general hardness or total hardness.
Bicarbonate / Alkalinity (HCO₃⁻)
Bicarbonate acts as a buffer — it neutralizes acids as they're extracted from the coffee bed. A little buffering capacity is stabilizing and prevents an overly sharp, sour cup. Too much, and bicarbonate actively cancels out the acidity that gives specialty coffee — particularly light and medium roasts — its brightness and complexity, producing a flat, muted, chalky result instead.[4] This is the single parameter water chemists watch most closely, because unlike total hardness, the acceptable range for alkalinity is narrow.[1]
pH
Ideal brewing water sits close to neutral, roughly 6.5–8.[1] Water that's too acidic can corrode brewing equipment and unbalance the cup toward excess sourness; water that's too alkaline suppresses acidity and flattens flavor. pH interacts closely with alkalinity — the two are related but not identical measurements.
Sodium (Na⁺) & Chloride (Cl⁻)
Present in smaller concentrations in most water sources, sodium and chloride don't drive extraction the way calcium and magnesium do, but low concentrations of chloride are associated with enhanced perceived sweetness without contributing flavor of their own.[6] High sodium concentrations — most common in water-softened or salt-intruded supplies — can throw off the total hardness-to-alkalinity balance and are generally avoided in dedicated brewing water recipes.
Chlorine & Chloramine
Not naturally occurring — added during municipal water treatment for disinfection. Even at concentrations too low to taste in water alone, chlorine and chloramine produce a distinctly unpleasant, medicinal off-flavor once brewed into coffee.[5] Any brewing water, tap or otherwise, should be free of both. A basic activated carbon filter removes the large majority of chlorine compounds.
05 / THE OFFICIAL STANDARD
The SCA Water Quality Standard
The Specialty Coffee Association — of which General Warfield's Coffee is a paid, current member — publishes a formal water standard built specifically around total hardness and alkalinity, the two parameters research has shown to most directly govern both extraction quality and equipment safety.[1][2] The values below reflect the SCA/SCAE published targets:
| Parameter | SCA Target | Acceptable Range |
|---|---|---|
| Total Dissolved Solids (TDS) | 150 ppm | 75–250 ppm |
| Total Hardness (Ca²⁺ + Mg²⁺) | ~68 ppm CaCO₃ | 50–175 ppm CaCO₃ |
| Alkalinity (HCO₃⁻) | 40 ppm CaCO₃ | 40–75 ppm CaCO₃ |
| pH | 7.0 | 6.5–8.0 |
| Chlorine / Odor | None detectable — completely free of chlorine, hypochlorite, and chloramines | |
Source: SCAE Water Chart, Zurich University of Applied Sciences (Wellinger, Smrke & Yeretzian), commissioned by the Specialty Coffee Association of Europe. Full citation below.
06 / COMPARING YOUR OPTIONS
Tap, Distilled, Filtered, or Bottled?
Every water source lands somewhere different on the TDS spectrum. Here's roughly where common options fall relative to the SCA target range:
Approximate TDS by water source. Actual tap water values vary significantly by municipality — testing your own supply is the only way to know where you fall.
| Water Type | Typical Result |
|---|---|
| Distilled / RO (untreated) | Flat, thin, underextracted — no minerals to drive extraction |
| Tap water (varies widely) | Inconsistent — depends entirely on local mineral content and chlorine treatment |
| Filtered tap (carbon filter) | Removes chlorine/odor but doesn't correct mineral imbalance |
| Distilled + mineral packet (e.g. Third Wave Water) | Consistent, repeatable, built to land inside the SCA range regardless of location |
| Very hard tap water | Muddy, chalky, bitter — over-mineralized, plus accelerated equipment scaling |
If You're Buying Bottled: What to Grab, What to Skip
Not every bottled water is created equal for brewing. A few widely available U.S. brands land close to the SCA range and work well; a few popular "premium" brands are actually too mineral-heavy and will flatten flavor or scale equipment over time.
| Brand | Approx. TDS | Verdict |
|---|---|---|
| Volvic | ~130 ppm | Good — consistently within SCA range, widely available |
| Crystal Geyser | ~90–100 ppm | Good — reliably close to SCA target, affordable |
| Deer Park | ~59–230 ppm (varies by spring source) | Good — usually within or close to SCA range, though multiple spring sources mean some bottle-to-bottle variability |
| Fiji | ~210–220 ppm | Borderline/avoid — sits at the upper edge of SCA range or above it |
| Evian | ~350+ ppm | Avoid for brewing — too mineral-heavy, will taste heavy/muted and accelerate scale |
| San Pellegrino | 1,000+ ppm | Avoid for brewing — far outside SCA range, great for drinking, bad for extraction and equipment |
TDS figures are approximate and can vary by bottling batch and region; brands sourcing from multiple springs (like Deer Park) will show more variation than single-source waters. When in doubt, check the brand's published water quality report or test with a pocket TDS meter directly.
General Warfield's Coffee is not affiliated with, sponsored by, or endorsed by any bottled water brand named above. Figures are drawn from publicly available water quality reports and third-party testing and are provided for general brewing guidance only — actual mineral content can vary by bottling date, region, and source. Always verify current TDS directly against a brand's published water analysis or your own meter reading if precision matters for your setup.
07 / SEE IT TESTED
Does Water Type Actually Change Coffee Taste?
We brewed the same beans, same grind, same technique — three different waters — and measured the results with a refractometer. Watch the full breakdown:
Same beans, same grind, same technique — the only variable across these three cups is the water.
Real beans, real water, real refractometer readings — no guesswork.
08 / TRY IT YOURSELF
A Simple Home Test You Can Run Today
You don't need a lab to see this effect for yourself. Here's a simple, low-cost way to taste the difference water chemistry makes:
A pocket TDS meter is all it takes to see where your own water falls against the SCA range.
What you'll need:
Your regular beans · a pocket TDS meter (inexpensive, widely available) · distilled water · a mineral-additive packet formulated for coffee (optional, for a third comparison point)
Steps:
- Measure your tap water's TDS with the meter. Note the reading.
- Brew a batch using your normal tap water — same beans, same grind, same ratio you always use.
- Brew a second batch identically, but swap in plain distilled water.
- If you have a mineral packet, brew a third batch with distilled water plus the packet, mixed per its instructions.
- Taste all three side by side, ideally lukewarm rather than hot — it's easier to detect flatness or muddiness once the coffee cools slightly.
Most people find the distilled-only cup noticeably flatter and thinner than expected, even with excellent beans — a direct, tastable demonstration of why minerals matter for extraction, not just theory on a page.
Want the science behind the beans themselves?
Explore the largest coffee glossary online — 3,000+ terms and counting.
EXPLORE THE GLOSSARY09 / THE BOTTOM LINE
The Bottom Line
Water isn't a background detail in coffee — it's 98% of the cup, and it's the single variable most people never think to control. The takeaways that matter most:
- Minerals drive extraction. Calcium and magnesium pull flavor compounds out of coffee during brewing — water with too few minerals (distilled, reverse osmosis) will taste flat no matter how good the beans are.
- Alkalinity is the parameter to watch most closely. Too much bicarbonate buffers away the acidity that gives specialty coffee its brightness and complexity.
- The SCA standard gives you real numbers to target — roughly 150 ppm TDS, 50–175 ppm total hardness, and 40–75 ppm alkalinity — not vague advice to "use good water."
- Your results will vary by location. Tap water quality differs dramatically by municipality, so testing your own water is the only way to know where you actually stand.
- Consistency beats guesswork. Whether it's a mineral-dosed distilled water, a well-matched bottled brand, or a filtered and tested tap source, the goal is a repeatable result — not a one-time lucky cup.
Good beans set the ceiling. Good water is what actually lets you reach it.
10 / FREQUENTLY ASKED QUESTIONS
FAQ
Can I just use bottled spring water?
Sometimes — it depends entirely on the brand. Mineral content in bottled spring water varies enormously, from nearly distilled to well outside the SCA range. Check the label's mineral content before assuming it's ideal for brewing.
Is my tap water automatically bad for coffee?
Not necessarily. Some municipal water supplies land naturally close to the SCA range. Others are far outside it, either too soft or too hard. The only way to know is to test it — tap water quality varies dramatically by region and even by neighborhood.
Does water quality matter as much for espresso as for pour-over?
Water chemistry matters for both, but the ideal target ranges can shift slightly with brew ratio — espresso's much lower ratio of water to coffee means the same water plays a proportionally larger role in a smaller volume, making equipment scaling risk and extraction sensitivity both more pronounced.[7]
What's the cheapest way to control my water?
A basic pocket TDS meter (a few dollars) to test what you're starting with, combined with a carbon filter pitcher to remove chlorine, covers most of the problem for most people. For full control, distilled water plus a coffee-specific mineral packet gets you into the SCA range consistently regardless of your local supply.
Will better water make cheap coffee taste like specialty-grade coffee?
No — water chemistry optimizes extraction of the flavor compounds that are actually present in the bean. It can't add complexity that isn't there from sourcing and roasting in the first place. Think of it as removing a ceiling, not adding a floor.
SEE IT IN ACTION:
Terms like TDS, extraction yield, and water hardness are fully defined in our glossary — the largest coffee reference resource online.
11 / REFERENCES
Sources & Citations
- Wellinger, M., Smrke, S., & Yeretzian, C. (Zurich University of Applied Sciences). The SCAE Water Chart. Commissioned by the Specialty Coffee Association of Europe.
- Specialty Coffee Association of America (SCAA). SCAA Standard: Water for Brewing Speciality Coffee. November 21, 2009.
- Hendon, C., Colonna-Dashwood, L., & Colonna-Dashwood, M. (2014). "The Role of Dissolved Cations in Coffee Extraction." Journal of Agricultural and Food Chemistry, 62(21), 4947–4950.
- Colonna-Dashwood, M. & Hendon, C. (2015). Water for Coffee. Self-published, Bath, UK.
- Lockhart, E.E., Tucker, C.L., & Merritt, M.C. (1955). "The Effect of Water Impurities on the Flavour of Brewed Coffee." Journal of Food Science, 20, 598–605.
- Gardner, D.G. (1958). "Effect of Certain Ion Combinations Commonly Found in Potable Water on Rate of Filtration Through Roasted and Ground Coffee." Journal of Food Science, 23, 76–84.
- Navarini, L. & Rivetti, D. (2010). "Water Quality for Espresso Coffee." Journal of Food Chemistry, 122, 424–428.
General Warfield's Coffee is a paid member of the Specialty Coffee Association (SCA). This article was written and technically reviewed in-house to reflect current SCA water quality standards.
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