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Colorado tap water and your coffee, city by city

Most of it starts as snow. How hard it is by the time it reaches your kettle depends on where you live.

Quick answer: is Colorado tap water good for coffee?

Mostly yes. Colorado's big city systems draw on mountain snowmelt, and most of them deliver water that is soft to moderately hard. Boulder's is soft. Denver's and Durango's sit in the moderately hard band. Aurora's is hard, and Pueblo's is the hardest of the cities we checked. The Specialty Coffee Association's water spec for tasting coffee asks for calcium hardness of 50 to 175 ppm and alkalinity at or near 40 to 70 ppm. On calcium hardness, even Pueblo's average fits. Alkalinity is where most Colorado cities run high.

CityTotal hardness, average (range)Alkalinity, averageClass on the USGS scale
Boulder44 mg/L (median)38 mg/LSoft
Denver105 mg/L (55 to 124)65 mg/LModerately hard
Durango (southwest Colorado)109 mg/L (73 to 148), or 6.38 grains per gallon96 mg/LModerately hard
Aurora136 mg/L (87 to 198)85 mg/LHard
Pueblo183 mg/L (137 to 217)93 mg/LVery hard, just over the line

Hardness is given as calcium carbonate. Denver's, Durango's and Aurora's figures come from their 2026 reports, which cover 2025. Pueblo's come from its 2025 finished water summary. Boulder publishes a median on its water quality data page. The class column applies the scale the U.S. Geological Survey uses, as Wikipedia lays it out: 0 to 60 mg/L soft, 61 to 120 moderately hard, 121 to 180 hard, 181 and up very hard.

Where each city's water starts

Almost all of it starts as snow, which is why the numbers are modest. Hardness is, in the City of Durango's words, a measurement of dissolved minerals, mainly calcium and magnesium. Wikipedia notes that water picks those up when it moves through rock such as limestone and gypsum. Snowmelt collected high in the mountains has had less time to do that.

  • Denver Water draws from the upper South Platte River, the upper Blue River and tributaries of the Fraser River, and stores water in mountain reservoirs including Cheesman and Dillon.
  • Boulder's supply depends on snowpack at the headwaters of North and Middle Boulder Creek. The remaining third comes from the Colorado-Big Thompson and Windy Gap projects, which bring upper Colorado River water across the Divide.
  • Aurora gets 95 percent of its water from surface sources in the Colorado, Arkansas and South Platte river basins, carried from as far as 180 miles away. The other 5 percent comes from deep aquifer wells.
  • Pueblo's water starts in the mountains above Leadville, flows down the Arkansas River and is piped from Pueblo Reservoir to the Whitlock treatment plant.
  • Durango's water comes mainly from the Florida River, with the Animas River also listed as a source.
  • Colorado Springs Utilities gets about 75 percent of its water from mountain streams, collected more than 100 miles away near Aspen, Leadville and Breckenridge. It does not print one hardness figure on its water quality page: the answer depends on which treatment plant serves you.
  • Fort Collins draws from the upper Cache la Poudre River and Horsetooth Reservoir. Its 2025 report does not list a hardness figure.

Hardness also moves with the seasons. Denver Water says its water is slightly harder in winter and softer from late spring through fall, when runoff dilutes the minerals, and that its southern collection system runs moderately hard while the northern one is somewhat soft. Pueblo reports the same pattern: lower hardness in summer with snow runoff, higher in winter.

What hardness and alkalinity do to a cup

Brewing is extraction, and Wikipedia's coffee preparation article lists water of balanced mineral composition among the basics, next to the right dose, time and temperature. The SCA's spec for tasting water sets that balance: no chlorine, calcium hardness of 50 to 175 ppm, alkalinity at or near 40 to 70 ppm and a pH of 6 to 8. Note that the SCA counts calcium hardness, while most utilities report total hardness, which also includes magnesium. Aurora reports both: 136 mg/L total and 112 mg/L calcium hardness on average. Pueblo's calcium hardness averages 138 mg/L, inside the SCA's range even though its total hardness is not.

Alkalinity is the other number to watch. Durango's report defines it as water's capacity to neutralize acid. The pleasant brightness coffee people call acidity comes from acids in the bean, so water with a lot of alkalinity has more capacity to blunt it. That is our reading of the definitions, not a lab test, and it is one reason a coffee can taste flatter in one town than in another. Durango, Aurora and Pueblo all average above the SCA's 40 to 70 band. Denver's 65 is inside it, and Boulder's 38 sits just under.

Hard water also leaves scale. Wikipedia describes limescale forming in kettles and water heaters, and the National Coffee Association says minerals in tap water build up in coffee makers, with manufacturers recommending a descale every 3 to 6 months. In Pueblo or Aurora, keep to the short end of that range.

Practical fixes, by city

  1. Start with cold tap water, filtered if you can. That is the National Coffee Association's advice for drip, pour over, French press and espresso alike.
  2. Skip distilled and softened water. The NCA says to avoid both. Wikipedia notes that softened water can carry higher levels of sodium or potassium.
  3. If you taste chlorine, Boulder's own tip works anywhere: leave water in an uncovered container in the fridge overnight and the chlorine dissipates.
  4. In Pueblo and Aurora, descale the brewer and kettle on schedule, and if a coffee tastes dull, try it with bottled spring water once to see whether the water is the cause.
  5. In Durango, hardness is moderate but alkalinity averages 96 mg/L, above the SCA's band, so filtered water is worth a side-by-side taste.
  6. In Boulder and Denver, the tap is already close to the SCA's range. Spend the effort on fresh beans and the grind instead; our pour over ratio chart is the place to start.

Brewing in the mountains adds a second variable, a lower boiling point. Our guide to high altitude coffee brewing covers that part.

Local water, local beans

Good water only helps if the beans are fresh. Buying from the roasters in this state shortens the trip from roaster to kitchen and keeps the money here. The Fourteener Coffee Club sends a 12 oz bag from a different independent Colorado roaster each box, every 2 or 4 weeks, at $16.99 a bag. Your first bag is free and you pay $7.99 shipping on that first box. Skip or cancel anytime. Build your plan.

Colorado water and coffee questions

Is Denver tap water hard or soft?

Denver Water calls it soft to moderately hard. Its 2026 report gives an average total hardness of 105 mg/L for 2025, with a range of 55 to 124, and says the water is slightly harder in winter.

Which Colorado city has the hardest water for coffee?

Of the cities we checked, Pueblo. Its 2025 finished water summary averages 183 mg/L total hardness, and Pueblo Water describes its water as hard to very hard.

Should I use softened water for coffee?

No. The National Coffee Association says to avoid distilled or softened water. Use cold tap water, filtered if possible.

Does boiling make hard water softer?

Partly. Wikipedia explains that the temporary hardness caused by dissolved bicarbonates can be reduced by boiling, which is what leaves scale in a kettle. Permanent hardness from sulfates and chlorides stays.

Sources

By Joe McRose, Fourteener Coffee Club. Updated . Hardness, alkalinity and water sources from each city's own water quality report or data page (Denver Water, City of Boulder, City of Durango, Aurora Water, Pueblo Water, Colorado Springs Utilities, Fort Collins Utilities); the hardness scale from Wikipedia; brewing water specs from the SCA and the National Coffee Association.