From the ground…

Two mineral powders for coffee brewing water.

Distilled, reverse osmosis and other pure water have almost none of the minerals that help shape how coffee tastes. GroundWater adds them back: one scoop of each per gallon.

Check your tap waterGet launch updates

Rain falls almost pure. On its way through the ground, it picks up minerals.

Calcium and magnesium

Bicarbonate

…to the grounds.

A cup of coffee is almost entirely water. The minerals in that water help shape how the coffee tastes.1

The two GroundWater jars: the larger HARD hardness blend and the smaller ALK alkalinity blend.

GroundWater, before launch

Two jars. Two matched scoops. One gallon.

Mineral powders for brewing water. Distilled or RO water is the ideal start. In some cities, tap water is already low in minerals, and a recipe for it is on the way.

See how it worksFind your city

Pure water is missing what coffee needs.

Pure water has almost nothing dissolved in it. Distilled and reverse osmosis (RO) water are the common kinds, and filters made to remove nearly all minerals can get there too. That makes pure water a clean, consistent place to start, and many cafés and home brewers now brew with it.

Hot water pulls flavor out of the coffee grounds. Bicarbonate provides alkalinity: the water's capacity to neutralize acids. It helps shape how much acidity reaches the cup, and its effect depends on how you brew.2 Calcium and magnesium contribute hardness and can interact with compounds in coffee.34 Pure water gives you a consistent starting point for choosing both.

Most pitcher and fridge filters take out chlorine and odors and leave most of the minerals in. If your tap water is high in minerals, a pitcher filter won't fix that, so start from distilled or RO. If your tap is already low in minerals, check the Tap Map.

Two settings shape brewing water.

Hardness calcium and magnesium, the minerals that interact with coffee compounds.34

Lower hardness. Fewer calcium and magnesium ions.

Our default.

Higher hardness. More calcium and magnesium ions.

Alkalinity bicarbonate, the buffer for acidity.2

Less buffer. More acidity remains.

Our default.

More buffer. More acidity neutralized.

Turning the dials. HARD and ALK come in separate jars so you can change one without touching the other.

  • More HARD: more calcium and magnesium.
  • Less HARD: less calcium and magnesium.
  • More ALK: more of the coffee's acidity is neutralized.
  • Less ALK: more of the coffee's acidity stays in the cup.

Start with the default. Change one jar at a time so you can taste what it does.

Hardness and alkalinity also matter for equipment. Check the finished water against your machine maker's specification.5

Tap water gets its minerals from the ground it ran through, so how much, and which ones, change from town to town and season to season. GroundWater chooses them on purpose. It starts from pure water and adds calcium, magnesium and bicarbonate back in measured amounts, from three food-grade mineral salts. See how your town's tap compares.

Calcium, from gypsum.

Food-grade gypsum is the same calcium salt used to set tofu and to adjust brewing water for beer. Calcium is one of the two hardness minerals.

Gypsum

Calcium sulfate dihydrateCaSO4·2H₂O

Adds
Ca2+ calcium, with sulfate
Jar
HARD
Why this salt
Calcium paired with sulfate rather than chloride. It raises hardness and leaves alkalinity alone.

Ingredient 01

Magnesium, from Epsom salt.

Magnesium is the other hardness mineral. Food-grade Epsom salt and gypsum share one jar: HARD, our hardness blend. HARD dissolves in seconds with mixing.

Epsom salt

Magnesium sulfate heptahydrateMgSO4·7H₂O

Adds
Mg2+ magnesium, with sulfate
Jar
HARD
Why this salt
The magnesium partner to gypsum, also a sulfate. Together they set hardness in one jar.

Ingredient 02

Alkalinity, from potassium bicarbonate.

Alkalinity is the water's ability to buffer acids. It softens the coffee's acidity and shapes whether brightness tastes lively or sharp.

Potassium bicarbonate

Potassium hydrogen carbonateKHCO3

Adds
HCO3− bicarbonate, with potassium
Jar
ALK
Why this salt
The potassium form of bicarbonate, the buffer that fresh water carries naturally. It raises alkalinity and leaves hardness alone.

Ingredient 03

Three food-grade ingredients. Separate hardness and alkalinity.

Fillers
None. The only ingredients are the three salts above: no fillers, flow agents or anticaking agents.
Buffer
Potassium bicarbonate, the potassium form of bicarbonate. Baking soda is the sodium form.
Hardness
Calcium sulfate and magnesium sulfate. Espresso machine makers limit chloride in their water specifications because it can be corrosive at brewing temperatures.5 Compare the complete finished-water profile with your machine maker's specification.
Default
HARD adds hardness. ALK adds the bicarbonate that buffers acidity. Separate jars keep the two settings independent, with a scoop matched to each powder. One default recipe today; other recipes will be described only after they pass blind testing.
The two GroundWater jars side by side: the larger HARD hardness blend, gypsum and Epsom salt, and the smaller ALK alkalinity blend, bicarbonate.
HARD scoopALK scoop

One scoop of each into a gallon.

  1. 1gallon

    Start with pure water, such as distilled or RO. Choose water with almost nothing dissolved in it. A water tester (a TDS meter) should read close to zero.

  2. 1HARD scoop

    One level scoop of HARD, with the HARD scoop.

  3. 1ALK scoop

    One level scoop of ALK, with the ALK scoop.

  4. Mix

    Mix until dissolved, then brew the way you already do.

Brewing by the jug? Keep the ratio: five of each for five gallons. Any clean jug or bucket works. Each jar has its own scoop, matched to that powder, so a level scoop is the dose. No weighing, no math.

Tap Map

Is your tap already close?

In some cities, tap water picks up almost no minerals on its way to you. Search about 7,600 U.S. cities to see whether yours is already low in minerals.

Find your city
Low-mineral tap water

Designed by a chemical engineer.

GroundWater was designed by Ben Huffer, a chemical engineer with a master's in environmental engineering. He chose each salt for what it adds and what it leaves out, kept the hardness and the buffer in separate jars, and matched each scoop to its powder.

Taste claims about GroundWater itself will come only from blind testing.

Sources

  1. Navarini, L. and Rivetti, D. (2010). Water quality for espresso coffee. Food Chemistry 122(2), pp. 424-428. Read the source
  2. Wellinger, M. Water and Coffee Acidity: How to Adapt Your Water for Different Extraction Methods. Specialty Coffee Association, 25 Magazine, Issue 9. Explains how alkalinity buffers coffee acids and why its effect depends on beverage ratio, including filter and espresso. Read the source
  3. Hendon, C. H., Colonna-Dashwood, L. and Colonna-Dashwood, M. (2014). The role of dissolved cations in coffee extraction. Journal of Agricultural and Food Chemistry 62(21), pp. 4947-4950. Calculations of how dissolved ions bind to selected coffee compounds. Read the source
  4. Bratthäll, T., Figueira, J. and Nording, M. L. (2024). Influence of divalent cations on the extraction of organic acids in coffee determined by GC-MS and NMR. Heliyon 10(5), e26625. Experiments with calcium and magnesium chloride found limited changes in selected acid concentrations at typical drinking-water mineral levels. Read the source
  5. La Marzocco, Water specifications. Discusses mineral content, acidity, chloride, corrosion, scale and water-level sensors. Compare the complete finished-water profile with the specification for your machine. Read the source

Talk to Ben.

GroundWater is coming to Kickstarter. Write to Ben, the founder, directly, and you'll hear the day it opens. Questions are welcome too.

ben@groundwaterminerals.com