USGS Water-Quality Assessment • Grains Per Gallon (gpg) & mg/L
Water Hardness by ZIP Code Chart (2026 US City Lookup)
Direct Answer: The US Geological Survey (USGS) classifies water hardness as Soft (0–3.5 gpg / 0–60 mg/L), Moderately Hard (3.5–7.0 gpg / 61–120 mg/L), Hard (7.0–10.5 gpg / 121–180 mg/L), and Very Hard (>10.5 gpg / >180 mg/L). Cities like Las Vegas (17.5 gpg), Phoenix (16.8 gpg), San Diego (16.1 gpg), and Los Angeles (14.2 gpg) suffer severe appliance limescale without whole-home treatment.
2026 US Metro Water Hardness Chart (Ranked Hardest to Softest)
| Metro / City | Primary ZIP Range | Hardness (gpg) | Hardness (mg/L / ppm) | USGS Classification | Recommended System |
|---|---|---|---|---|---|
| Las Vegas, NV | 89101 – 89148 | 17.5 gpg | 299 mg/L (ppm) | Extremely Hard | SpringWell CF1 + SS1 Combo → |
| Phoenix, AZ | 85001 – 85254 | 16.8 gpg | 287 mg/L (ppm) | Extremely Hard | SpringWell CF1 + SS1 Combo → |
| Los Angeles, CA | 90001 – 91401 | 16.4 gpg | 280 mg/L (ppm) | Very Hard (~280 ppm TDS) | SpringWell CF1 + SS1 Combo → |
| San Diego, CA | 92101 – 92130 | 16.1 gpg | 275 mg/L (ppm) | Very Hard | SpringWell CF1 + SS1 Combo → |
| Tampa, FL | 33601 – 33647 | 12.6 gpg | 215 mg/L (ppm) | Very Hard | SpringWell CF1 + SS1 Combo → |
| Fresno, CA | 93701 – 93730 | 11.4 gpg | 195 mg/L (ppm) | Very Hard | SpringWell CF1 + SS1 Combo → |
| Houston, TX | 77001 – 77098 | 9.1 gpg | 156 mg/L (ppm) | Hard | Aquasana Rhino EQ-1000 → |
| Chicago, IL | 60601 – 60657 | 8.2 gpg | 140 mg/L (ppm) | Hard | SpringWell CF1 + SS1 Combo → |
| Dallas, TX | 75201 – 75248 | 7.9 gpg | 135 mg/L (ppm) | Hard | Aquasana Rhino EQ-1000 → |
| Philadelphia, PA | 19102 – 19148 | 7.6 gpg | 130 mg/L (ppm) | Hard | Aquasana Rhino EQ-1000 → |
| Sacramento, CA | 95811 – 95835 | 5.8 gpg | 99 mg/L (ppm) | Moderately Hard | SpringWell CF1 + SS1 Combo → |
| Miami, FL | 33101 – 33186 | 5.4 gpg | 92 mg/L (ppm) | Moderately Hard (Lime-Softened) | Aquasana Rhino EQ-1000 → |
| Denver, CO | 80202 – 80238 | 5.2 gpg | 89 mg/L (ppm) | Moderately Hard | Aquasana Rhino EQ-1000 → |
| Charlotte, NC | 28202 – 28277 | 2.1 gpg | 36 mg/L (ppm) | Soft | Aquasana Rhino EQ-1000 → |
| Atlanta, GA | 30301 – 30327 | 1.8 gpg | 31 mg/L (ppm) | Soft | Aquasana Rhino EQ-1000 → |
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