{
  "city": "Madison",
  "state": "WI",
  "slug": "madison",
  "hardness_facts": [
    {
      "utility": "Madison Water Utility",
      "measure": "Hardness, citywide",
      "value_as_published": "18-20 grains per gallon",
      "period": "Undated FAQ",
      "source_title": "Madison Water Utility: Water Quality Frequently Asked Questions",
      "source_url": "https://www.cityofmadison.com/water/water-quality/faq"
    },
    {
      "utility": "Madison Water Utility",
      "measure": "Hardness, Unit Well 6",
      "value_as_published": "450 mg/L (26 grains per gallon)",
      "period": "Calendar year 2025",
      "source_title": "Unit Well #6 water quality report",
      "source_url": "https://www.cityofmadison.com/water/documents/water-quality/Well06QualityReport.pdf"
    },
    {
      "utility": "Madison Water Utility",
      "measure": "Hardness, Unit Well 14",
      "value_as_published": "580 mg/L (34 grains per gallon)",
      "period": "Calendar year 2025",
      "source_title": "Unit Well #14 water quality report",
      "source_url": "https://www.cityofmadison.com/water/documents/water-quality/Well14QualityReport.pdf"
    }
  ],
  "published_span_mg_per_l": [
    308,
    580
  ],
  "span_converted_from_grains": true,
  "usgs_class": "very hard",
  "usgs_class_source": "https://www.usgs.gov/water-science-school/science/hardness-water",
  "notes": [
    "Hardness differs from well to well. The 22 well reports we read give 270 to 580 mg/L, and nine of them are harder than the citywide FAQ figure."
  ],
  "local_details": {
    "disinfectant": {
      "text": "Madison Water Utility disinfects with chlorine and says it does not use chloramine.",
      "kind": "chlorine",
      "source_title": "Madison Water Utility water quality FAQ",
      "source_url": "https://www.cityofmadison.com/water/water-quality/faq",
      "evidence_ids": [
        "MADISO-L-01"
      ]
    },
    "source_water": {
      "text": "Madison water is all groundwater, pumped by 21 active wells from a deep sandstone aquifer under the city.",
      "source_title": "Madison Water Utility water quality report",
      "source_url": "https://www.cityofmadison.com/water/documents/water-quality/WaterQualityEnglish.pdf",
      "evidence_ids": [
        "MADISO-L-02"
      ]
    },
    "by_area": {
      "text": "Each Madison well serves its own part of town, and the utility publishes a separate quality report for each well, so water differs by neighborhood.",
      "source_title": "Madison Water Utility water quality report",
      "source_url": "https://www.cityofmadison.com/water/documents/water-quality/WaterQualityEnglish.pdf",
      "evidence_ids": [
        "MADISO-L-03"
      ]
    }
  },
  "sources_checked_on": "2026-10-27",
  "site": "https://madisonwatersystems.com/",
  "brand": "Madison Water Systems by My Home Water System",
  "taking_requests": false
}