Quick summary: To measure water hardness, you can test for calcium and magnesium levels using DIY test kits, simple at-home methods or professional water testing. Results are typically expressed in grains per gallon (gpg), parts per million (ppm) or milligrams per liter (mg/L). Professional testing provides the most accurate measurement and helps determine the right treatment solution.
Water hardness is measured by the concentration of calcium and magnesium minerals in your water, typically expressed in grains per gallon (gpg), milligrams per liter (mg/L) or parts per million (ppm). These measurements show whether your water is soft, hard or somewhere in between.
Hard water is one of the most common water quality issues homeowners face, often leaving mineral buildup on fixtures, spots on dishes and residue that can dry out skin and hair. But before you can measure and address hard water, it’s helpful to understand what water hardness actually means and how it affects your home.
What is water hardness?
Water hardness refers to the amount of dissolved calcium and magnesium minerals in your water supply. These hardness minerals naturally accumulate when water flows through rocks and soil that contains these minerals, like limestone. The higher the mineral content, the harder your water becomes.
Hard water is generally not a health risk for drinking water, but it can cause issues around your home due to the mineral buildup it causes, known as hard water scale. Scaling is a common sign of elevated hardness levels. It forms when calcium and magnesium remain behind after water evaporates or heats, leaving chalky buildup on faucets, showerheads, glass, plumbing fixtures and water-using appliances. Over time, hard water scale can become harder to clean and may affect water flow or appliance efficiency, which is why measuring your water hardness is an important first step toward choosing the right solution.
How to measure water hardness levels
Water hardness is often measured in grains per gallon (gpg) of calcium carbonate, milligrams per liter or parts per million, which are equivalent. The scales are as follows:
| Water Hardness Levels | |
|---|---|
| Soft | Less than 1 gpg |
| Slightly hard | 1.0 to 3.5 gpg |
| Moderately hard | 3.5 gpg to 7.0 gpg |
| Hard | 7.0 to 10.5 gpg |
| Very hard | Over 10.5 gpg |
The scales above are based on information from the Water Quality Association, though various sources list these categories with slightly different measurements. For instance, this water hardness scale shared by the USGS breaks down results in mg/L as follows:
- Between 0 and 60 mg/L is considered soft
- Between 61 and 120 mg/L is considered moderately hard
- Between 121 and 180 mg/L is considered hard
- More than 180 mg/L is considered very hard
To use the same gpg hardness scale above, you can simply convert your ppm or mg/L by dividing that number by 17.1 to find the gpg equivalent. So, for example, 130 mg/L or ppm would be 7.6 gpg, which is considered hard water.
How to test for water hardness
Depending on the source of your water, you may be more or less likely to have hard water problems, and well water users are particularly susceptible to this issue.
Check with your water supplier
This isn’t an option for households that use well water, but if you have city water and you suspect you may have problems with hardness, you might want to contact your supplier as a first step.
Your local water supplier’s website and annual water quality report are good places to begin acquiring information about general water hardness levels in your area. However, the information included in annual reports varies by location, so your supplier may not provide specific data on this topic. Plus, hardness is not only determined by the source of your water; it also can accumulate more hardness minerals as it travels to your taps. This means that even in the same neighborhood, water hardness levels can even vary from home to home.
Try a DIY hard water test
Determining whether or not you have water hardness doesn’t have to be complicated. One quick way to check is by looking for visible limescale buildup around faucets, showerheads and sinks.
Alternatively, you can conduct a simple at-home test with just a clear bottle and a few drops of pure liquid soap. Here’s how to check your water:
- Fill the bottle one-third full with tap water.
- Add a few drops of the liquid soap.
- Close the lid and shake vigorously for 5–10 seconds.
If the water forms fluffy bubbles and looks mostly clear, your water is likely soft. On the other hand, if the water looks cloudy, milky or produces very few suds, you may have hard water.
This method doesn’t give exact hardness levels, but it’s a helpful first step.
Get your home’s water tested
To find out about the specific hardness levels in your home water supply currently, you’ll have to conduct testing.
There are a variety of different home testing kits available for determining the relative concentration of hardness minerals in your home water supply. In-home and IL EPA-certified lab testing options are available from water treatment professionals like Culligan, too. Working with a water treatment company can help you get accurate results, understand how to interpret them and identify what steps to take next.
Your local Culligan experts will test your water and provide personalized recommendations for the right solution for your home.
Schedule your free water test.
Choosing the right water softener
If you do have hard water, a water softener can help rid your home of issues like limescale buildup, dry hair and skin, spotty dishes and inefficiency of water-using appliances.
With a reliable water hardness test and information about your household water usage, you’ll be able to work with a professional to determine what kind of water softener will best suit your needs. Based on where your home water supply falls on the hardness scale, how much water you use and other factors, you can choose the best water softener that suits your requirements.
Water hardness FAQs
Water hardness can affect parts of your home in different ways. These answers can help you better understand what hardness levels mean, how testing works and when it may be time to consider water treatment.
What minerals cause water hardness?
Water hardness is mainly caused by calcium and magnesium. These minerals occur naturally and can enter your water as it moves through rock, soil and underground formations.
What is the best way to measure water hardness?
Professional water testing is typically the most accurate way to measure water hardness. DIY test strips and simple at-home soap tests can provide a general indication of hardness levels, but professional testing delivers more precise measurements and can help identify other water quality concerns that may influence treatment recommendations. A free in-home water test from Culligan can help determine your water hardness level and identify the right treatment solution for your home.
Is hard water the same as contaminated water?
No. Hard water is caused by naturally occurring minerals such as calcium and magnesium, not contaminants. While hard water can create issues like scale buildup, soap residue, spotty dishes and dry-feeling hair or skin, it is generally considered a water quality issue rather than a contamination issue.
How does a water softener address hard water?
A water softener helps reduce hard water by removing the calcium and magnesium minerals that cause it. As water passes through the system, these minerals are captured by specialized resin beads. The system periodically uses a brine solution to rinse the minerals away and restore the resin’s ability to soften water. This process helps reduce scale buildup and allows softened water to flow throughout your home.
When should I test my water hardness?
You should consider testing your water hardness if you notice limescale, spots on dishes, reduced water flow, stiff laundry, soap that does not lather well or dry-feeling hair and skin after bathing. Testing can also be helpful before choosing a water softener so the system can be matched to your home’s needs.
Take action against hard water
Hard water is not something you have to live with. If you’re noticing signs such as scale buildup, spotty dishes, soap residue or dry-feeling hair and skin, the first step is understanding what’s in your water.
A free in-home water test from your local Culligan expert can help identify your water hardness level and uncover other water quality concerns that may be affecting your home. Based on your results, your Culligan specialist can recommend a customized water softening solution designed for your household’s needs.
Schedule your free in-home water test today to get started.