What is Hard Water?

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Around 80% of homes in the US have hard water, but half of these households don’t even know what hard water is.

Hard water is something of a buzzword in today’s world. We know it’s bad, and we know there are ways to get rid of it – but how is it formed, and where does it come from?

In this ultimate guide, we’ve answered all your questions about water hardness. Stay tuned for a hard water definition, and keep reading to learn how hard water is formed, how to know if you have hard water, and how to get rid of water hardness for good.

📖Hard Water Definition

According to the Water Quality Association“Hard water (or water hardness) is a common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements.” The two minerals responsible for hard water are largely calcium carbonate and magnesium ions. Iron and trace metals can also be found in hard water.

Soft water contains very few hard minerals. The more hardness minerals water contains, the harder it is.

⏲The Water Hardness Scale

Water hardness varies across the country. To work out exactly how hard your water is in comparison to the average water hardness, you can look at the water hardness scale.

Water hardness is a measurement of calcium carbonate in milligrams per liter (mg/L) or parts per million (PPM) as calcium carbonate equivalent. PPM and mg/L are equal measurements that can be used interchangeably.

It can also be measured in grains per gallon (GPG). Some hardness testing kits provide results in GPG, rather than mg/L.

Hardness measurements are slightly different, depending on where online you look. But these scales should give you a good indication of water hardness.

HardnessGrains per Gallon (GPG)Parts per Million (PPM) & mg/L
Soft<1 0 – 17
Slightly Hard1.5 – 517 – 60
Moderately Hard3.5 – 7 60 – 120
Hard7 – 10120 – 180
Very Hard>10>180
water hardness scale

🏔 How Hard Water is Formed

What makes water hard? Let’s look at how hard water is formed.

Some municipal water is sourced from surface water sources (streams, lakes, and rivers), but ~78% of public water comes from groundwater sources, like underground aquifers (pockets of water).

Regardless of where water comes from, before it reaches water treatment plants, it comes into contact with rocks and soils in the natural environment.

The earth naturally contains limestone, chalk, and gypsum. When water flows across surfaces containing these deposits, some of the deposits break off and dissolve in water.

Water is known as a universal solvent, and it’s true that water can dissolve more substances than any other aqueous solution. That’s how mineral ions from the environment end up in our water supplies, causing high total hardness levels.

Water Hardness Map
Source: United States Geological Survey (USGS)

🔍 How to Know if you Have Hard Water

It’s usually pretty obvious if your water is hard. There are a few signs to look out for:

  • Spotting on your dishes, glassware, and cutlery
  • Feeling a sticky film on your skin after showering or washing your hands
  • Dry skin and hair problems
  • Reduced water pressure in your home
  • Increased cleaning duties
  • Chalky white mineral deposits around your faucets, on your showerhead, and in your toilet bowl
  • Rich mineral taste in drinking water
  • More soap required in washing machines and dishwashers
Scale on a faucet caused by hard water

🔬Testing your Water Hardness

An even easier way to know if your water is hard is to test a water sample in your home.

There are two methods of testing your drinking water:

  • Use an at-home test kit
  • Send of a sample of your water to a laboratory

At-home test kits are affordable and provide instant results.

water hardness test strips

To use an at-home test kit, follow the instructions on the packet – which will probably go like this:

  1. Fill a glass (or fill the included vial, if you have one) with normal cold drinking water from your tap.
  2. Insert the test strip and leave it submerged in the water for several seconds, as advised in the instructions.
  3. When you remove the strip, it should have changed color. Compare the color of the strip to the included color chart. Find the closest match to a color on the chart corresponding to your water hardness, usually in grains per gallon (GPG).

Laboratory testing is the more thorough, costly alternative to at-home testing kits. If you want to know exactly how hard your water is, in PPM or mg/L, you’ll get this from a laboratory test.

tap score water hardness report

Depending on the laboratory you choose (we recommend a certified laboratory, like SimpleLab), the testing process should go something like this:

  1. The laboratory sends you a test kit and instructions in the post.
  2. You fill the included vial (s) with a sample of your water and send the kit back to the laboratory by post.
  3. The laboratory tests your water and delivers your test results, usually over email, within two weeks.

Getting your water tested by a laboratory is obviously better, but it doesn’t matter if you decide to buy an at-home testing kit instead. You’ll still get a good idea of the mineral content in your water, and your test results are available instantly, which is a bonus.

water testing with tap score

📌The Damaging Effects of Hard Water

You know the water hardness signs to look out for, but what’s so damaging about hard minerals?

Here, we’ve shared all the bad stuff about calcium and magnesium dissolved in your water supply. You’re going to want to reduce your home’s water hardness level after you’ve read this section.

effects of hard water in a home

Reduces Appliance Efficiency

Appliances have much shorter lifespans when used with water containing elevated levels of hardness ions, compared to water with low hardness or no hardness.

Scale formation in appliances slows water flow and forms a layer of insulation on surfaces, requiring appliances to work harder to do their jobs.

Increases the Cost of Living

Reduced appliance efficiency isn’t only bad for the environment – it also causes your energy bills to increase.

For instance, your water heater will spend longer heating your water – and you’ll pay for every extra second that your heater stays on.

Not only that, but water with a high total hardness doesn’t lather well with soap, so you end up spending more money on using more soap than you need in your washing machine and dishwasher.

Makes Cleaning A Chore

There are some cleaning jobs – like feather dusting and knocking air into cushions – that are just easier than others. And there are some – like breaking your arm scrubbing a crusty limescale stain – that are just harder.

Imagine how much easier life would be if you didn’t have to clean the after-effects of water hardness. You might actually manage to stick to a weekly bathroom cleaning schedule.

Clogs Plumbing

If you have a coffee pot that you haven’t deep-cleaned in a really long time, you’ll probably have noticed how quickly limescale builds up on surfaces. But at least you can clean your coffee pot – just imagine what the inside of your plumbing looks like.

Even water with a moderate hardness deposits layer after layer of mineral stains inside pipes, which gradually decrease water pressure and reduce the open space that water can flow through. Eventually, you’ll need to replace your plumbing altogether.

Dries out Skin and Hair

Calcium and magnesium minerals form a nasty layer of something called soap scum on your skin and hair.

Soap scum is a sticky layer of stuff that forms when the fatty acid in shampoos and soap reacts with hardness ions. Soap scum is difficult to wash away, and ends up lingering on our skin and hair, clogging our skin’s pores and causing dry hair and split ends.

Makes your Dishes Look Unwashed

Spotty dishes, cutlery, and glassware are common side-effects of water hardness. If your dishes dry with white, milky stains on their surfaces after you’ve washed them, you won’t be able to get them looking shiny and clean with your own water supply.

The mineral-rich chalky residue left on your kitchenware is unpleasant to look at and near-impossible to remove.

Damages Showerheads and Faucets

High hardness levels have the most noticeable effect on your faucets and showerheads. When water moves through these appliances, it leaves deposits of calcium, magnesium and other minerals on their surfaces.

You’ll find more limescale on your hot water faucets because hardness ions thrive in hot water. If you’ve noticed your polished chrome faucets turning crusty and gray-white, total water hardness is to blame.

showerhead with limescale buildup

✔️ How to Get Rid of Hard Water

If you want to wave goodbye to the effects of water hardness, consider these temporary and permanent solutions. Skip to the permanent solutions if you’re looking for the most effective way to remove calcium and magnesium.

Temporary Solutions

If you just want to avoid the effects of water hardness in the short term, there are a few temporary solutions. Keep in mind, though, that these solutions are only really ways to fight elevated water hardness levels, rather than getting rid of it altogether.


Cleaning the effects of water hardness – i.e. mineral scale – will get rid of the problem after it has already happened.

White vinegar, baking soda, citric acid, and lemon juice are effective natural cleaners for calcium and magnesium scale deposits. Spritz or sprinkle your cleaner of choice onto affected surfaces in your home and leave for between five and 20 minutes before scrubbing off with a clean cloth or sponge.

For tough mineral stains, you’ll get the best results from leaving a vinegar-soaked cloth over a surface for at least one hour.

Once you get rid of scale buildup, it’ll only be a matter of time before it returns. Unfortunately, cleaning is something you’ll be lumped with for life if you choose to stick with hard water.

cleaning limescale off faucet

Buy Bottled Soft Water

Some types of bottled water contain low levels of magnesium and calcium. If you don’t want to use hard water for certain tasks in your home – such as washing your face, washing the dishes, or filling your coffee pot – you could use bottled soft water instead.

As you can imagine, this gets expensive pretty quickly. Plus, you couldn’t use bottled water in appliances that draw water directly from your water supply, such as your washing machine, your water heaters, and your dishwasher.

Permanent Solutions

There are two highly effective permanent solutions for tackling calcium and magnesium in your water supply: water softeners and water conditioners.

water softener and water conditioner

Water Softeners

Water softening systems are designed to eliminate calcium and magnesium by drawing them out of your water supply. Traditional salt-based softeners replace these minerals with sodium (salt).

A water softener is installed at the point where your water supply enters your home. When water enters the water softening system, it flows through a resin tank. The calcium carbonate and magnesium ions are attracted to the resin and stick to its surface. Meanwhile, equal parts sodium are released into the water to balance out its charge.

The result is that the hard minerals are trapped inside the water softening system, while soft water leaves the system to flow through your plumbing.

Here’s why we love water softeners:

  • They’re pretty low-maintenance, only requiring salt top-ups every month or so
  • They have really good lifespans. The resin lasts for around 10 years with proper pretreatment if applicable, while the system itself lasts for more than two decades
  • They physically remove calcium and magnesium from water, getting rid of the causes of water hardness and completely eliminating scale
  • They can deal with high concentrations of hardness ions
  • They also get rid of iron, a trace metal that’s particularly common in well water
  • Considering how long they last and the money they save, they’re pretty affordable ($1,000-$1,500 upfront for a system lasting more than 20 years)

👉 See our picks for the best water softener systems in 2024

Water Conditioners

Water conditioners are an effective alternative to water softeners in the right water quality conditions. If you don’t fancy adding salt to your water, consider water conditioners.

Rather than replacing calcium carbonate and magnesium with salt, water conditioners alter the form of these minerals, crystallizing them and preventing them from sticking to surfaces as scale.

Water conditioners use a single tank to condition water. When water flows through the tank, a conditioning process, such as template-assisted crystallization, takes place. When water leaves the tank, the hardness ions are no longer able to deposit in your plumbing and appliances.

Here’s why we love water conditioners:

  • They don’t need salt to operate, and they don’t need to regenerate, so they’re cheaper to run and don’t waste water
  • Because they’re saltless, they’re maintenance-free. The conditioning media lasts for 6-10 years
  • They greatly reduce limescale issues without removing healthy calcium carbonate or magnesium from water
  • They don’t affect your water quality. Water still tastes the same after using a conditioner
  • They’re another affordable long-term solution, the average system costing around $1,250-$1,750 upfront, with no annual maintenance cost

👉 Check out our favorite water conditioners here.

💬Hard Water FAQ

Is hard water dangerous to health?

No, hard water is rarely dangerous to health. The dissolved calcium and magnesium in hard water are actually beneficial to our health, and we need them in our daily diets. Of course, it’s possible to overdose on these minerals, but you’re highly unlikely to do this, even if you drink very hard water.

In fact, there are a couple of studies that show weak correlations between water hardness and cardiovascular health, showing that cardiovascular disease has a lower risk factor in people who drink water with high total hardness, compared to those who drink soft water.

The only properly known health effects of water hardness are on skin and hair. These aren’t dangerous, though – just damaging.

Why is hardness a problem?

Water hardness causes expensive damage in your home, makes cleaning much more difficult, and dries out your skin and hair.

If you need help understanding why hardness is a problem, imagine if it didn’t exist. Without limescale, your appliances would last longer, your cleaning duties would be halved, and your skin and hair would be healthier and smoother.

Do you need to treat hard water?

No. Nobody needs to treat water hardness. In fact, many people ignore hard water damage and simply consider it an unavoidable side-effect of being a homeowner. But if you want to prevent damage to your plumbing and appliances, treating water hardness is the obvious solution.

What is acceptable water hardness PPM and GPG?

Between 0 and 100 parts per million (PPM) is acceptable water hardness. 101-150 PPM of hardness is slightly hard, so you may also consider this to be acceptable. Anything above 151 PPM will have noticeable effects in your home.

If you’re using testing strips that measure hardness in GPG (grains per gallon), water hardness of between 0 and 3 indicates that you have soft water that doesn’t need to be treated. 3-7 GPG is moderately hard water that has mild effects in your home. Anything over 7 GPG is above acceptable water hardness.

Is water hardness regulated in the US?

No. The EPA, which regulates harmful contaminants in public water systems, doesn’t have a standard or legal limit for hardness in water supplies. This is because calcium and magnesium aren’t toxic or dangerous to health.

Remember that water is a universal solvent, which means that most public water supplies naturally contain hardness ions. The goal of water treatment facilities is to produce clean, potable water, by removing lead, pharmaceuticals, VOCs, arsenic, and other metals that are generally considered dangerous to drink. The mineral ions that make water hard aren’t dangerous, so they’re not a top priority to remove in the water treatment process.

Why don’t all states have the same water hardness?

Water hardness varies depending on the geology in your local area. Some states naturally have more mineral-rich rocks in their earth, resulting in a higher mineral content in their groundwater.

Hardness minerals aren’t removed from public drinking water supplies, so the city water and private well water in your local area should have similar hardness measurements. However, rural areas often have higher hardness levels than built-up cities.

What’s the difference between temporary hardness and permanent hardness?

Temporary hardness is caused by dissolved calcium bicarbonate and magnesium bicarbonate, while permanent hardness is caused by dissolved sulfate and chloride compounds. Boiling water reduces temporary water hardness, but has no difference on permanent hardness.

Is tap water considered hard water?

It depends on where you live – but usually, yes. Tap water in the US is typically considered hard. If your tap water leaves limescale deposits on surfaces, it’s hard.

Is hard water OK to drink?

Yes, hard water is fine to drink. Moderate or high calcium and magnesium concentrations are safe and healthy in our drinking water. The major problem with hard water is the expensive damage caused by mineral buildup, and there are no consequences for drinking hardness minerals.

Does boiling water remove hardness?

Sometimes. Boiling water can only be used to reduce temporary hardness, so it might not work in your home. It depends what kind of hardness you’re dealing with. In most cases, boiling water isn’t an effective solution.

What do you do when you have hard water?

The most common solution to hard water is to purchase a water softening system. Water softeners prevent scale deposits, either by removing dissolved minerals or crystallizing them. There are varying degrees of water hardness, and you’ll probably base your reaction on how hard your water is.

Of course, you don’t have to do anything if you have hard water. But if you value your hard-earned money, and you don’t want to waste it on unnecessary bills, buying a water softener just makes sense.

Is hardness a water quality issue?

Yes. Poor-quality water doesn’t have to taste bad or be dangerous to drink. Hardness affects water quality because it causes damage like clogged pipes, soap scum, delayed water flow and decreased water pressure, and dry skin and hair. You wouldn’t have these water quality issues with soft water.

Can a water filter soften water?

No. Water filters remove harmful contaminants from water, but they’re not designed to deal with water hardness. In fact, high concentrations of calcium carbonate and magnesium damage most filter media. You need  a water softener to produce soft water in your home. Softening doesn’t make pure water – only some kinds of water filters, like reverse osmosis filters, are capable of that.

Are water softeners suitable for me?

Yes – if you have the budget and you want to improve the quality of water in your home. Ion exchange systems are suitable for most people. If you have high blood pressure and you’re on a low-sodium diet, you should look at salt-free water conditioners, or use potassium chloride rather than sodium chloride in a traditional salt-based water softener.

We have lots of resources on water softeners, including our updated complete water softener guide, which is the place to head next if you’re keen to learn more about how water softeners work and whether they’re worth the money.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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