Water Hardness
by ZIP Code
Geological monitoring data from 330,000+ USGS stations, aggregated to your county.
Franklin County, OH
Estimated natural water hardness: 120 PPM — Moderately Hard
Understanding Water Hardness
Water hardness is caused by dissolved calcium and magnesium minerals. Hard water leaves white scale deposits on faucets, reduces soap lathering, and can shorten the life of water heaters and appliances. Hardness is measured in mg/L (PPM) or grains per gallon (GPG).
What Is Water Hardness?
Water hardness is the concentration of dissolved minerals in your water supply, primarily calcium carbonate (CaCO₃) and magnesium. These minerals originate from geological formations like limestone and dolomite rock. As water moves through the ground, it dissolves small amounts of these minerals, carrying them into aquifers, wells, and municipal water systems.
Hardness is measured as the total concentration of calcium and magnesium, expressed in milligrams per liter (mg/L), also called parts per million (PPM). The higher the concentration, the “harder” the water. In the United States, approximately 85% of homes have some degree of hard water.
How dissolved minerals from underground rock make your water hard
What Causes Hard Water?
Rainwater is naturally soft — it contains almost no dissolved minerals. However, as it percolates through soil and rock, it picks up calcium and magnesium ions from geological formations. The type of bedrock in your region determines how hard your water becomes.
Limestone & Chalk
The most common cause. These calcium carbonate rocks dissolve easily in slightly acidic rainwater, releasing Ca²⁺ ions into groundwater.
Dolomite
Similar to limestone but also contains magnesium carbonate, contributing both Ca²⁺ and Mg²⁺ to water hardness.
Gypsum Deposits
Calcium sulfate deposits cause “permanent” hardness that cannot be removed by boiling, unlike carbonate-based hardness.
Well vs. Surface Water
Well water typically has more contact time with underground rock, making it harder than surface water from lakes or rivers.
Regional variation is significant: areas with deep limestone aquifers (much of the Midwest and Great Plains) tend to have very hard water, while regions with granite or volcanic bedrock (Pacific Northwest, New England) typically have softer water.
Hard Water Effects on Skin & Hair
Hard water is one of the most common household complaints, and its effects on skin and hair are the most immediately noticeable. The dissolved calcium and magnesium minerals interact with soap and your body’s natural oils in ways that can cause real discomfort.
Mineral residue left on skin after washing blocks moisture absorption, disrupts the skin’s natural barrier, and can aggravate conditions like eczema and dermatitis. For hair, calcium and magnesium deposits coat the hair shaft, stripping natural oils and leaving it dry, brittle, and prone to breakage. Over time, hard water buildup can make hair look dull and feel rough.
Note about babies and children: Infant skin is thinner and more sensitive than adult skin. Studies have shown that children in hard water areas are more likely to develop eczema. If your home has hard water and you have young children, a shower filter or whole-house softener can make a meaningful difference.
Is Hard Water Safe to Drink?
Yes, hard water is generally safe to drink. The calcium and magnesium that make water hard are actually essential minerals that contribute to your daily nutritional intake. The World Health Organization (WHO) states that there are no health-based guidelines needed for water hardness.
In fact, some research suggests that drinking hard water may provide a modest cardiovascular benefit due to its magnesium content. Your body needs both calcium and magnesium daily, and hard water can be a supplementary source.
However, there are a few caveats:
- Taste: Very hard water (above 180 ppm) can have a noticeable mineral or chalky taste that some people find unpleasant.
- Residue: Hard water can leave mineral deposits on fixtures, glasses, and kettles, though this is an aesthetic issue, not a health concern.
- Lead pipes caution: In older homes with lead plumbing, hard water can slightly increase lead leaching into drinking water. If your home was built before 1986, consider having your water tested for lead regardless of hardness level.
Water Hardness by State
Click a state to see county-by-county water hardness data. Colors show the dominant hardness classification.
View all states as list
PPM vs GPG — How Hardness Is Measured
Water hardness is reported two ways: mg/L (also called PPM, parts per million) is the standard scientific unit. GPG (grains per gallon) is commonly used by water softener companies. To convert: 1 GPG = 17.1 mg/L. For example, 120 mg/L ÷ 17.1 = 7.0 GPG.
Water Hardness Scale & Levels
The United States Geological Survey (USGS) classifies water hardness into four levels based on calcium carbonate concentration. This is the standard used across water utilities, testing labs, and water treatment professionals.
USGS water hardness classification scale — ppm (mg/L) and grains per gallon (gpg)
| Classification | mg/L (PPM) | Grains/Gallon | What to Expect |
|---|---|---|---|
| Soft | 0 – 60 | 0 – 3.5 | No scale, excellent soap lather |
| Moderately Hard | 61 – 120 | 3.5 – 7.0 | Minor spots, good lather |
| Hard | 121 – 180 | 7.0 – 10.5 | Scale buildup, reduced lather |
| Very Hard | > 180 | > 10.5 | Heavy scale, significant issues |
To convert between units: 1 GPG = 17.1 mg/L (PPM). Simply divide your PPM reading by 17.1 to get grains per gallon, or multiply GPG by 17.1 to get PPM.
How to Test Your Water Hardness
There are three common methods to test water hardness at home. Each offers a different balance of cost, accuracy, and convenience.
Test Strips
- Dip in water, compare color to chart
- Approximate reading (±25 ppm)
- Good for quick screening
- Available at hardware stores
Liquid Drop Kit
- Titration method — count drops until color change
- More accurate (±10 ppm)
- Measures in grains per gallon
- Reusable for many tests
Lab Test
- Send sample to certified lab
- Most accurate (exact ppm)
- Full mineral breakdown included
- Recommended for treatment decisions
Free option: Your water utility publishes an annual Consumer Confidence Report (CCR) that includes hardness data. Search for your utility’s name + “water quality report” or check the EPA’s CCR search tool.
Hard Water Damage to Your Home
Hard water doesn’t just affect your skin and hair — it takes a real toll on your home’s plumbing, appliances, and daily cleaning. The costs add up quickly over time.
Water Heater
Scale insulates heating elements, reducing efficiency by 25–40%. A water heater in a hard water area may last 6–8 years instead of 12–15.
Pipes & Plumbing
Mineral deposits narrow pipes over time, reducing water pressure and eventually requiring expensive repiping. Galvanized pipes are especially vulnerable.
Dishes & Glass
Cloudy white spots on glasses and dishes, film on shower doors, and calcium rings in toilets require constant cleaning with acidic products.
Laundry
Minerals bind with detergent, making clothes feel stiff and scratchy. Colors fade faster, whites turn gray, and you need 50–75% more soap.
The estimated cost of hard water damage to the average American homeowner is $800+ per year in extra energy consumption, increased soap and detergent use, premature appliance replacement, and additional cleaning products.
Water Softeners & Solutions
If your water hardness is above 120 ppm (7 GPG), a water treatment solution can save money, protect appliances, and improve your daily quality of life. Here are the three main approaches.
How a salt-based ion exchange water softener works
Salt-Based Ion Exchange Softener
The most effective method. Hard water passes through a resin bed that exchanges calcium and magnesium ions for sodium ions. Removes hardness completely, protecting all plumbing and appliances.
Cost: $500 – $3,000 installed • Ongoing: $5–10/month for salt • Best for: Whole-house treatment, water above 120 ppmSalt-Free Conditioner (TAC/Template Assisted Crystallization)
Does not remove minerals but changes their crystalline structure so they don’t form scale on surfaces. Water still tests “hard” but behaves differently. No salt, no drain, no electricity needed.
Cost: $300 – $2,000 • Ongoing: Minimal • Best for: Scale prevention, moderate hardness (60–120 ppm)Reverse Osmosis (Point-of-Use)
Filters water through a semipermeable membrane, removing virtually all dissolved minerals. Typically installed under the kitchen sink for drinking and cooking water only — not whole-house.
Cost: $200 – $500 • Ongoing: Filter replacement every 6–12 months • Best for: Drinking water improvementDIY solutions: White vinegar removes scale from fixtures and appliances. Shower head filters ($15–40) reduce mineral contact with skin and hair. Washing soda (sodium carbonate) added to laundry helps counteract hard water effects on clothes.
Hard Water & Plants, Pets & Aquariums
Hard water affects more than just people and plumbing. If you keep plants, pets, or aquariums, water hardness is an important factor to consider.
Houseplants & Gardens
Hard water gradually raises soil pH, making nutrients like iron and manganese less available. Acid-loving plants (azaleas, blueberries, ferns) are most affected. White mineral crust on soil is a telltale sign.
Aquariums
Fish species have specific hardness preferences. Bettas and tetras prefer soft water (under 75 ppm). African cichlids thrive in hard water (150–300 ppm). Check GPG levels before adding fish.
Pets
Dogs and cats generally handle hard water fine, but some pets may drink less from bowls with strong mineral taste. Hard water can also leave mineral deposits in water fountains and dispensers.
Tips
Use filtered or rainwater for sensitive plants and aquariums. Flush houseplant soil periodically to prevent mineral buildup. Test aquarium water hardness monthly with a GPG drop kit.
Frequently Asked Questions
What is water hardness?
Water hardness is a measure of dissolved calcium and magnesium minerals in water. These minerals dissolve from rock and soil as water moves through the ground. Hard water is not a health risk, but it causes scale buildup in pipes and appliances, reduces soap effectiveness, and can leave spots on dishes and fixtures.
What is the difference between PPM and GPG?
PPM (parts per million) and mg/L (milligrams per liter) are the same unit — the standard scientific measurement of water hardness. GPG (grains per gallon) is used mainly in the water softener industry. To convert: 1 GPG = 17.1 PPM. For example, 120 PPM equals about 7.0 GPG.
How is water hardness classified?
The USGS uses a four-level classification: Soft (0-60 mg/L), Moderately Hard (61-120 mg/L), Hard (121-180 mg/L), and Very Hard (above 180 mg/L). Water above 120 mg/L typically causes noticeable scale and soap issues.
Do I need a water softener?
If your water is above 120 mg/L (7 GPG), a water softener can help reduce scale buildup and improve soap lathering. For very hard water above 180 mg/L, a softener is strongly recommended to protect your water heater, dishwasher, and plumbing from mineral deposits.
Does water hardness affect health?
Hard water is generally safe to drink. Some studies suggest hard water may provide a small amount of dietary calcium and magnesium. However, very hard water can dry out skin and hair. Water softeners that use salt exchange calcium for sodium, which may be a concern for people on low-sodium diets.
Can water hardness vary within the same ZIP code?
Yes. If you are on a private well, your hardness depends on your specific aquifer. If you are on city water, hardness depends on where your utility sources water and whether they soften it. Our estimates reflect area-wide geological hardness — your actual tap water may differ.
Can hard water cause hair loss?
Hard water doesn't directly cause hair loss, but mineral buildup on the scalp can weaken hair follicles, cause breakage, and make hair appear thinner. The calcium and magnesium deposits coat the hair shaft, making it dry, brittle, and prone to snapping. Using a shower filter or chelating shampoo can help.
Does hard water cause eczema?
Hard water can aggravate eczema symptoms but doesn't cause the condition. The high mineral content disrupts the skin's natural barrier, strips moisture, and makes soap harder to rinse — leaving irritating residue. Studies show children in hard water areas have higher rates of eczema flare-ups.
Is hard water bad for plants?
Very hard water (above 180 ppm) can raise soil pH over time, making nutrients less available to acid-loving plants. Mineral deposits can also build up in soil and on leaves. For sensitive plants, use filtered or rainwater. Most garden plants tolerate moderate hardness well.
How much does a water softener cost?
A whole-house salt-based water softener typically costs $500 to $3,000 installed, depending on capacity, brand, and local labor. The unit itself is $400 to $1,500, with installation adding $200 to $500. Ongoing costs include salt ($5-10 per month) and occasional maintenance. Salt-free conditioners range from $300 to $2,000.
What is the difference between a water softener and a water conditioner?
A water softener removes calcium and magnesium through ion exchange, replacing them with sodium. A water conditioner (also called descaler or TAC system) doesn't remove minerals — it changes their structure so they don't form scale. Softeners are more effective but require salt; conditioners are maintenance-free but less effective for very hard water.
Does boiling water remove hardness?
Boiling removes temporary hardness (caused by calcium bicarbonate) by converting it to insoluble calcium carbonate, which precipitates out. However, permanent hardness (caused by calcium sulfate and magnesium compounds) is NOT removed by boiling. For comprehensive softening, you need a water softener or reverse osmosis system.