
Understanding water hardness: Definition and measurement of hard water

La good water quality that we use at home, for hydration, washing or cooking, is one of the major concerns of consumers, and quite rightly so! In France, tap water is perfectly safe to drink and its quality is closely monitored by regional health agencies. However, depending on your region, department or commune, its mineral content, taste or even the quality of the water may vary. hardness may vary.
What is hard water?

La water hardness is a parameter that measures the quantity of minerals, mainly calcium and magnesiumpresent in the water. This indicator is expressed by a hydrotimetric titre (TH)which is expressed in French degrees (°F).
Each French level corresponds to a concentration of 4 mg/l of calcium or 2.43 mg/l of magnesium, or a concentration of 10 mg of limestone per litre of water. Limestone is a form of calcium carbonate (CaCO3) that forms when minerals in water combine with carbon dioxide from the air.
So, for example, if the water has a hardness of 20 °F, this means it contains 80 mg/l of calcium (20 x 4) or 48.6 mg/l of magnesium (20 x 2.43), or 200 mg/l of limestone (20 x 10).
The different degrees of water hardness and their corresponding calcium and magnesium concentrations
Degree of hardness | Water content (°F) | Calcium concentration (mg/l) | Magnesium concentration (mg/l) |
---|---|---|---|
Very soft | <8 | <32 | <20 |
Sweet | 8 – 15 | 32 – 60 | 20 – 36 |
Moderately hard | 15 – 25 | 60 – 100 | 36 – 61 |
Hard | 25 – 40 | 100 – 160 | 61 – 97 |
Very hard | >40 | >160 | >97 |
The values shown in the table above are general indications and are not intended to be exhaustive. may vary from one region to another.
It is important to note that water hardness can vary according to geographical location and the type of water used. geological features of the regionand the source of the water used. In fact, regions where the water is in contact with limestone rocks tend to have harder water, while regions with higher acid soils have softer water.

Water hardness by municipality
Overall, there are 3 simple ways to find out this information.
Visit the Ministry of Health website
First of all, you need to know that the Ministry of Health provides information on water quality for each region and town. You can find information on water hardness for your region by visiting Ministry of Health website and consulting the section on water quality. This option may be useful if you wish to obtain an estimate of the water hardness in your area without carrying out a test.
On the water bill
The water hardness can also be indicated on your water bill. However, this is not always the case. Nevertheless, if the water hardness is not shown on your bill, you can contact your local water company to obtain this information.
Read also: What is the price per m3 of water in France and in my municipality?
Perform a TH water hardness test

Finally, the most reliable way of determining water hardness is to do the following a TH water hardness test. These tests are available in most DIY and gardening shops. You can also find them on the Internet for an average cost of around €10.
The TH water hardness tests use strips or test kits to measure the level of minerals in water. These kits contain chemicals that react with the minerals in the water to produce a colour. The colour produced is then compared to a colour scale to determine the hardness of the water in French degrees.
Is hard water bad for your health?
NO! It needs to be said and repeated, hard or chalky water is not harmful to your health. On the contrary, it has the advantage of providing essential minerals such as calcium and magnesium that are important for human health. Calcium and magnesium are essential elements provided by nature that help strengthen bones, maintain healthy blood pressure and support the nervous and muscular systems.
What's more, the minerals present in hard water are beneficial for cardiovascular health helping to reduce the risk of heart disease. Studies have also shown that hard water can help reduce the risk of certain chronic diseases, such as kidney disease, tooth decay and osteoporosis.
Read also:Â Calcium / calcium ion in drinking water, the whole truth!
So what are the harmful effects of hard water?
If there are water softeners So when you see it on sale, you're going to ask us: "What are the harmful effects of hard water?
In fact, when hard water is heated, the minerals are deposited in the form of limescale. This scale can build up in pipes, water heaters, washing machines and dishwashers, reducing the efficiency and operation of household appliances.
The perfect example of the disadvantages that can be caused by water that is too hard is scaling of your kettle !

Not only can limescale reduce the efficiency of the kettle by increasing the time it takes to heat the water, it can also alter the taste of boiled water. In addition, deposits can cause premature wear of the kettle's heating element, which could lead to costly repairs or premature replacement of the appliance.
On this subject, we recommend that you read our article on How to descale a kettle and extend its lifespan.
Do I need a water softener?
There are several methods of treating hard water. One of the most common options is to use a water softener. This device uses an ion exchange resin to replace calcium and magnesium ions with sodium ions (yes, salt!), thus reducing the amount of minerals in the water.
Other options include the use of water filters and deionisation systems. But the question remains: Is it really useful?
Negative environmental impact
First of all, it's worth noting that a water softener can be harmful to the environment for a number of reasons.
First and foremost, water softeners use salt to remove hard water minerals such as calcium and magnesium. When the water softener is regenerated, a large quantity of salty water is discharged into the sewer system, which eventually ends up in the surrounding watercourses. This salt water can be toxic for plants and animals.
Then, of course, a water softener is a must. energy-hungry and requires more water to operate. Finally, the manufacture of a water softener requires the production of materials that are often non-recyclable.
What about my household appliances?
Yes, this is the clincher for selling you a water softener! The appliance will protect your household appliances from the negative consequences of limescale, as discussed above. Will it?
Nothing could be further from the truth! The softener removes the calcium from your water, making it acidic as well as make it corrosive by adding salt! Is it really better than hard water for your household appliances?
So what can you do? There are alternative solutions which we describe in our article Which household anti-limescale system should I choose? that won't turn your tap water into seawater, but are still environmentally friendly!
Read also:Â Why install a water softener?
That's it, we hope you now know everything there is to know about water hardness and its measurement. We also hope to have convinced you that the concept of water hardness is mainly put forward by softener manufacturers who are trying to convince you that hard water is bad for your health, which is completely false.
Alternatives to conventional water softeners
If water hardness can cause problems for your household appliances, there's no need to resort to traditional salt-based softeners, which are often expensive and, as we've seen, not very environmentally friendly.
There are alternative solutions, such as ionic anti-limescale systems. For example ODOUCE anti-limescale system by LAVIE is an innovative salt-free alternative. Thanks to its patented technology, it prevents the formation of limescale by transforming it into a non-sticky powder that is easy to remove. Easy to install and maintenance-free, ODOUCE effectively protects your equipment while preserving the quality of your water, without the drawbacks of conventional softeners.
FAQ on hard water and measuring water and hard water
What is water hardness?
Water hardness is a measure of the concentration of dissolved minerals, mainly calcium and magnesium. Expressed in French degrees (°f), each degree corresponds to 4 mg/L of calcium or 2.4 mg/L of magnesium. Hard water is therefore rich in these minerals.
What is the water hardness scale?
To measure water hardness, we use a scale in French degrees (°F), which indicates the amount of calcium and magnesium present. Here are the different categories:
Very mild: <8 °F
Mild: 8 - 15 °F
Medium hard: 15 - 25 °F
Hard: 25 - 40 °F
Very hard: >40 °F
How can I find out the hardness of the water in my locality?
- Ministry of Health website Visit the water quality section for your region.
- Water bill Hardness is sometimes indicated on your water bill.
- Hardness test Use test kits available in shops or online to obtain an accurate measurement.
Is water hardness the same throughout France?
No, water hardness varies from region to region. For example, the north-east of France has particularly hard water, while Brittany has softer water.
Is hard water bad for your health?
No! Hard water is not harmful to your health. In fact, it provides essential minerals such as calcium and magnesium, which are beneficial for bone health and the cardiovascular system.
What are the disadvantages of hard water?
Hard water can cause limescale deposits in household appliances and pipes, reduce the effectiveness of soaps and detergents, and leave skin and hair dry.
What are the disadvantages of water that is too soft?
Water sweet may sound nice, but it's not without its faults! In fact, it's often more corrosive, which isn't great for your pipes and equipment. It can lead to more wear and tear, especially if you have metal pipes. What's more, very soft water lacks minerals that are good for us, like calcium and magnesium. And, let's be honest, it sometimes tastes a bit bland, whereas slightly harder water has that little something extra that makes it pleasant! So it's all a question of balance.
Do I need a water softener?
A water softener can be useful if you have limescale problems. However, it's important to note that softeners use salt, which can be harmful to the environment. There are also alternatives such as water filters and magnetic devices that modify the structure of limescale.Â
Does hard water affect the taste of water?
Yes, hard water can have a more mineralised taste, which can alter the flavour of foods and drinks prepared with it.
Are there salt-free water softeners?
Yes 😊 We told you aboutODOUCE from LAVIE, but you can also find all the anti-limescale systems in our article : Which household anti-limescale system should I choose?
You may also be interested in these articles on tap water quality:
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