Water hardness in Boulder
2.5 gpg soft
Tap water in Boulder is soft: 2.5 gpg (42 mg/L · 2.4 °dH · 4.2 °fH).
Source: City of Boulder Drinking Water Quality Monitoring Program page (hosts 2026 Drinking Water Quality Report, 2025 data) (2026) · data checked 2026-10-23
Boulder takes about two-thirds of its water from Middle and North Boulder Creek, including snowmelt stored in Silver Lake and Barker reservoirs, and the rest from Colorado-Big Thompson and Windy Gap water. High-mountain snowmelt over crystalline rock holds few minerals, so hardness is a soft 42 mg/L CaCO₃. Scale is rarely a problem.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 2.5 gpg |
|---|---|
| Utility | City of Boulder Utilities (Drinking Water Quality Program) |
How Boulder compares
- Tap water in Boulder is 73 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 1242 of 1372 in the United States (1 = hardest); 9 % of these cities have softer water.
- In Colorado it is number 9 of 11 cities; the regional median is 6.1 gpg.
- Nearest city with clearly softer water: Longmont, 22 km away (1.3 gpg).
- Nearest city with clearly harder water: Broomfield, 19 km away (4.8 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Little or no limescale in kettles, water heaters or washing machines.
- Soap lathers easily; water does not dry skin or hair.
- Dishwasher: salt setting at minimum or off.
- No softener needed; a jug filter only changes taste.
How much salt will you use for softening?
No. Water this soft does not need softening.
Descale a coffee machine or kettle about every 6 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Boulder
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 2 °dH |
| AEG / Electrolux | 1 |
| Beko | 1st |
| Hoover | S0 |
| LG | H0 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Boulder water hard or soft?
It is soft: 42 mg/L as CaCO₃ (2.5 gpg, 2.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Boulder safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
How many grains per gallon is Boulder water?
2.5 gpg, equal to 2.4 °dH, 4.2 °fH or 42 mg/L calcium carbonate.
What dishwasher salt setting should I use in Boulder?
For 42 mg/L (2.4 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Boulder?
No. With soft water a softener adds nothing.
Source
Source: City of Boulder Drinking Water Quality Monitoring Program page (hosts 2026 Drinking Water Quality Report, 2025 data) (2026). Method: figure published by the water supplier. City of Boulder Drinking Water Quality Monitoring Program page (hosts 2026 Drinking Water Quality Report, 2025 data) · Outdated figure? Tell us