Water matters
At some point every coffee nerd has to do a piece on coffee water. It is, after all, the main ingredient in our favorite beverage. The topic can get genuinely extensive and intimidating; the rabbit hole is deep, and others have explored far deeper than I ever could. This is a condensed, easy-to-implement version with just a handful of points that have made an appreciable difference in my brews without overcomplicating my brewing.
For a proper deep dive, I recommend the Coffee Chronicler's guide to the best water for coffee, which even includes a TLDR section. He also offers a paid course if you seek true mastery. My other favorite source is James Harper's The Science of Coffee podcast (Filter Stories)— he has several excellent episodes on optimizing water, and he's a joy to listen to.
What to measure
TDS, GH, and KH
The Chronicler's TLDR is handy, but I think it over-simplifies a bit: it's worth spending a few dollars on a simple fish-tank test kit to check the GH (General Hardness) and KH (Karbonat Hardness, or alkalinity / water's buffering capacity) in your tap water.
• TDS (Total Dissolved Solids) is the overall mineral load measured by simple conductivity. A cheap TDS meter is the best place to start and the easiest way to tell if your tap water is drifting over time. Keep in mind that consumer-level meters don't correct for water temperature, and it makes a big difference — always measure water that's settled to room temperature.
• GH is the calcium and magnesium salt concentration.
• KH is alkalinity, which buffers against acidity.
My target ranges
Here's the simple starting point that has served me well. You can absolutely tune these to taste or to match specific roasts, but these numbers get you into a good place. If your current numbers are way off from these, try tweaking your brews a bit before dismissing what might be a significant taste change – I genuinely believe you’ll find better cups overall if you give these a chance.
• TDS between 40 and 150 ppm (I prefer 50–75)
• GH between 40 and 80 ppm
• KH between 25 and 65 ppm
• GH should be higher than KH (ideally around 2:1, but don't stress the ratio)
I'd be a little more flexible on the GH and KH numbers and a little more focused on the TDS range — it's the anchor that tells you when your tap water has changed.
Simplified Workflow
Most people can build a very good coffee water by blending tap water with filtered water. If that doesn't get you there, try filtered plus bottled, or start from distilled water (in the US it's usually labeled for machine use, but it's perfectly safe to drink) and add a commercial coffee water mineral kit. You can tune the tap-to-filtered ratio by taste, but tap water changes over time, and re-tinkering blind is frustrating — you want anchoring numbers to work from. That's where the Culligan ZeroWater pitchers come in: they have a TDS meter built into the lid, which simplifies the whole workflow enormously. Yes, I’m plugging this product, but rest assured I have no conflicts of interest. You’ll need to ditch the filter (or get two of these if you don’t have a way to purify water already), but once you’ve figured out the ratio of purified water to tap water that achieves the parameter ranges above, you can then quickly mix your water in real time in the ZeroWater pitcher to dial in the TDS. I fill mine and store it in the fridge for nearly a week's worth of coffee water. Yes, it takes a bit more time and energy to heat in the kettle, but it's still fast enough that it's rarely a bottleneck in my sleepy morning pour-over routine. Remember, the TDS on the meter will drop by about 20 points once it’s in the fridge and this is simply an artifact of how TDS meters work.
Espresso tweaks
The same basic rules apply, but this is where you can really dial in acidity. Keep the TDS very low (15–30 ppm) if you want to emphasize acid notes, and bring it up (60–90 ppm) to smooth it over. You can do similar tricks with pour-over, but I find it most remarkable with espresso.
TLDR;
• Get a cheap TDS meter and a fish-tank test kit for GH/KH.
• Aim for TDS 40–150 ppm, GH 40–80, KH 25–65, with GH above KH. Find your favorite TDS with the water options available to you.
• Blend tap water with filtered water to hit your numbers.
• For espresso, drop TDS low for acidity, raise it to smooth things out.
