Hard Water
Hard water contains elevated levels of dissolved calcium and magnesium. It is not a health risk and is associated with some cardiovascular benefits, but it causes scale buildup in pipes and appliances, soap scum, and reduces the effectiveness of detergents. Approximately 85% of U.S. homes have hard water. It is an aesthetic and infrastructure issue, not a regulatory one.
Quick Reference · Hard Water
Quick Answer
Water hardness is a measure of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions, expressed in milligrams per liter (mg/L) as calcium carbonate (CaCO₃) or grains per gallon (gpg). Water below 60 mg/L is considered soft; 61–120 mg/L is moderately hard; 121–180 mg/L is hard; above 180 mg/L is very hard. The Colorado River, which supplies water to much of the Southwest, is among the hardest source waters in the U.S.
Why Is Hard Water in Drinking Water a Concern?
While hard water is not a health hazard, it has significant practical consequences: scale buildup reduces water heater efficiency by up to 30%, clogs showerheads and faucets, shortens appliance lifespan, and increases soap and detergent usage. Very hard water areas spend meaningfully more on plumbing maintenance.
Residents in the Southwest (Arizona, Nevada, Southern California), the Midwest (Indiana, Illinois, Kansas), and parts of Texas and Florida typically have the hardest water. Groundwater is almost always harder than surface water because it has more contact time with rock and soil.
Health Effects of Hard Water in Drinking Water
No known negative health effects — hard water is safe to drink
Some epidemiological studies suggest modest cardiovascular benefit from magnesium and calcium intake
Very hard water may worsen eczema in sensitive individuals (dermatological research is mixed)
High calcium intake from very hard water may contribute to kidney stones in susceptible individuals
How Does Hard Water Get Into Drinking Water?
Dissolution of limestone and dolomite rock formations
Groundwater contact with calcium- and magnesium-rich geology
Colorado River and its tributaries (exceptionally hard source water)
Agricultural return flows adding mineral content
Regulatory Limit
EPA Maximum Contaminant Level (MCL)
No federal limit
There is no EPA Maximum Contaminant Level for hardness — it is classified as a secondary (aesthetic) standard, not a primary health standard. The EPA's Secondary Maximum Contaminant Level (SMCL) recommendation for total dissolved solids (TDS), which correlates with hardness, is 500 mg/L for taste purposes only. Hard water does not trigger regulatory action.
How to Test for Hard Water in Your Water
Water hardness can be measured with inexpensive test strips, drop-count test kits, or through certified lab analysis. Your utility's Consumer Confidence Report typically includes hardness data. Most utilities also provide hardness information on their websites because it is a common customer question.
How to Remove Hard Water from Drinking Water
These treatment methods have demonstrated effectiveness for Hard Water removal.
Frequently Asked Questions
From Hard Water to Action
Find a certified lab to test for Hard Water
State-certified labs for PFAS, lead, nitrate, bacteria, and more
Water softener — mineral ion exchange
NSF certification details, cost range, and maintenance notes
Look up your specific utility's records
Search by ZIP code or utility name for compliance and PFAS data
Hard Water in California
State-specific violations, utilities, and testing guidance
Hard Water in Texas
State-specific violations, utilities, and testing guidance
Hard Water in Arizona
State-specific violations, utilities, and testing guidance
Data sources and methodology
How EPA compliance and UCMR 5 monitoring data is sourced and validated
Questions About Hard Water in Drinking Water
How do I test my water for Hard Water?
Find state-certified labs — confirm EPA Method 533/537.1 for PFAS
Which utilities have Hard Water violations?
Search by ZIP code or utility name for official EPA compliance records
What removes Hard Water from tap water?
Water Softener (Ion Exchange) — NSF certification details, cost, and maintenance
How is Hard Water data sourced on this site?
EPA SDWIS, UCMR 5, and CCR data sources — update cadence and accuracy notes
Related Pages
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Quick Reference
Category
Minerals
Risk Level
low
EPA Limit
No federal limit
Most at Risk
Residents in the Southwest (Arizona, Nevada, Southern California), the Midwest (Indiana, Illinois, Kansas), and parts of Texas and Florida typically have the hardest water.
Well Water Relevant
Yes
Hard Water by State
Treatment Options