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What is the Ideal Water Hardness Level? Get the Facts Here

Fact checked by Stephen Conklin

What is the Ideal Water Hardness Level

When getting a water softener, you may wonder, what is the ideal water hardness level? You can check out the American National Standards Institute definition of soft water to know the evaluation of calcium carbonate concentration in your water. In one standard rating system, hard water measures 150 to 300 mg/L (PPM) or 8.75 to 17.5 GPG.

While hard water can give you beneficial minerals, it can also wreak havoc on your water heater, dishwasher, and other water appliances, pipes, and fixtures. That is why you may need a water softener, depending on your home’s water hardness levels.

Table of Contents

What Makes Water Hard


The water that comes out from our faucets contains molecules other than H2O. It also contains dissolved minerals, such as magnesium carbonate, calcium carbonate, sulfate, and chloride.

These dissolved minerals are what make water hard, depending on their concentration. In general, the more dissolved particles in the water, the higher its hardness level.

Leading organizations, such as the World Health Organization and the US Geological Survey, simplify our understanding of water hardness as the amount of calcium and magnesium carbonates dissolved in the water.

Measures of Water Hardness

Water experts always express water hardness levels in milligrams per liter (mg/L). Some of us are more familiar with the term “parts per million” or PPM. Do not worry because these measurement units are the same.

As such, if you read a water hardness level of 100 mg/L, you know that the water contains 100 calcium or magnesium carbonate units for every million water units.

Many of us do not use either mg/L or PPM. We prefer using “grains per gallon” or GPG instead. If a water hardness test result is in PPM, you can convert it into GPG by dividing the PPM value by 17.14 (1 GPG = 17.14 PPM).

Hence, if a water tester shows you a water hardness level of 120 PPM, you know that it translates to about 7 GPG (120 ÷ 17.14 = 7.0017).

The Ideal Water Hardness Level


It may dishearten you to learn that there is no such thing as the ideal water hardness level. Organizations have different cutoff values, despite having the same evaluation parameter: calcium carbonate concentration.

For example, the US Environmental Protection Agency’s 2018 Water Quality Parameters classify water hardness as follows:

  • Soft water – Less than 75 mg of calcium carbonate per liter of water (PPM) or less than 4.37 GPG
  • Moderately hard water – 75 to 150 mg/L (PPM) or 4.37 to 8.75 GPG
  • Hard water – 150 to 300 mg/L (PPM) or 8.75 to 17.5 GPG
  • Very hard water – More than 300 mg/L (PPM) or 17.5 GPG

On the other hand, the US Geological Survey classifies hard water as follows:

  • Soft water – Less than 60 mg/L (PPM) or 3.5 GPG
  • Moderately hard water – 61 to 120 mg/L (PPM) or 3.56 to 7 GPG
  • Hard water – 121 to 180 mg/L (PPM) or 7.06 to 10.5 GPG
  • Very hard water – More than 180 mg/L (PPM) or 10.56 GPG or more

Individual scientists also offer a more detailed water hardness classification. For example, Bichi and Bello’s study proposed six water hardness categories.

  • Soft water – Less than 50 mg/L (PPM) or 2.9 GPG
  • Reasonably soft water – 50 to 100 mg/L (PPM) or 2.91 to 5.83 GPG
  • Slightly hard water – 101-150 mg/L (PPM) or 5.84 to 8.75 GPG
  • Reasonably hard water – 151-250 mg/L (PPM) or 8.76 to 14.59 GPG
  • Hard water – 251 to 350 mg/L (PPM) or 14.6 to 20.11 GPG
  • Very hard water – More than 350 mg/L (PPM) or 20.12 GPG

I know these figures are confusing. That is why I recommend using the American National Standards Institute definition of soft water. The organization defines soft water as water that contains less than a grain of calcium carbonate or any other hardness mineral per gallon of water.

Why Water Hardness Level Matter

Determining water hardness levels helps you decide whether to install a water softener or conditioner, or not. But first, let us talk about what hard water can do for and against you.

Hard water contains calcium, magnesium, and other minerals that can bring a number of health benefits.

For example, some studies show that hard water can protect against heart attack-related deaths. There is also evidence suggesting hard water can protect against pancreatic, rectal, colon, and gastric cancer. It can also safeguard teenagers and young children against atherosclerosis.

We know how calcium is good for the bones and muscles, as well as magnesium’s effects on exercise performance, blood pressure, and insulin sensitivity. Removing these minerals from water may not be a good idea for some people.

So, why do people want to soften their water?

Magnesium, calcium, and other dissolved minerals can clump together, forming scales on surfaces of water pipes, fixtures, and appliances. Limescale can reduce water flow and affect the performance of water appliances, such as water heaters, dishwashers, and washing machines.

Hard water also affects the cleaning capabilities of soaps and detergents. You will not get that much lather, regardless of how much you rub the soap on your hands. Washing your dishes and utensils can also leave a soapy residue, making these objects less than appealing.

Is it Time to Buy a Water Softener?

Some homeowners are fine with a water hardness level of 10 GPG, while others may want a lower rating of 7 GPG. As such, the decision to buy a water softener depends on what water hardness level you consider ideal for your needs.

You must know that most water treatment companies recommend a water softener for water hardness levels exceeding 15 GPG or over 300 PPM. This figure allows you to benefit from the dissolved minerals in your drinking water without harming your water fixtures and appliances.

If you value the minerals in your water, you may want to buy water conditioners instead. These devices do not remove the dissolved minerals; they only prevent them from adhering to surfaces and stop limescale formation. However, in the long term, to save the most money. I think you should consider water softeners like smart water softeners, portable water softeners, and the twin tank water softener.


What is the ideal water hardness level? This depends on what you consider a good balance between the health benefits of calcium and magnesium and their effects on water fixtures and appliances. Too low, and you might develop some serious health issues. Too high, and you can have problems with your plumbing.

You can always use a water softener or a water conditioner if the water hardness level is higher than what you expect. The trick is to choose which water hardness classification to use in interpreting the water test results.

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