Not all water is the same. Most people aren’t aware of the differences but hard water refers to water high in dissolved minerals, such as calcium and magnesium. Soft water, on the other hand, is either rainwater or treated water whose only ion is sodium.

Most groundwater is naturally hard to some extent since it picks up minerals as it percolates through the soil. These include chalk, lime, as well as calcium, and magnesium. If you’d be drinking water from a natural well system, the odds are it will contain hefty amounts of minerals.

Where do you draw the line between hard and soft water?

The answer to the question ‘what exactly is hard water?’ is a matter of mineral concentration, measured in milligrams per liter or grains per gallon.

Each country may have a different standard for what constitutes hard water, but in the United States, the American National Standards defines soft water as containing less than 17.1 mg/L. Although there are different standards in different parts of the world, generally speaking, the following levels be used to assess water hardness:

• 0-60 mg/L: soft
• 61-120 mg/L: moderately hard
• 121-180 mg/L: hard
• more than 180 mg/L: very hard

The most common dissolved minerals are calcium and magnesium, both alkaline earth metals found in the 2nd group of the periodic table. These elements have a 2+ charge so they lose two electrons to form cations, such as Ca²⁺ and Mg²⁺, which easily dissolve in water.

Which one is better?

It’s not a case where one is better than the other — it all depends on the application. Hard water contains essential minerals that the body needs for the growth and function of bones and muscles, as well as for regulating blood pressure and enzyme action. What’s more, hard water is not only healthier but also tastier, whereas soft water tastes salty. Research supported by the World Health Organization found soft water is unhealthy. So hard water is typically a better option for drinking (although in very high quantities, it’s still not recommended).

In all other instances, hard water is not desirable. Just take a look at your sink, washing machine, and teakettle. If you notice mineral deposits and stubborn white spots that can only be removed with extra scrubbing, hard water is the culprit.

Hard water makes your appliances work hard thereby raising energy bills, causing wear and tear on these appliances, and reducing the lifespan of your plumbing. According to a recent Water Quality Research Foundation study, appliances using soft water have a 30-50% longer life and use 27% less energy. This is why it’s worth investing in the best water softener system — they can be expensive but you actually save money over time by prolonging the lifespan of your washing machine and other appliances.

These undesirable effects are due to the properties of hard water. For instance, when water with a high content of dissolved minerals is heated, it often leaves a coating on pots or containers. That’s because the solution forms calcium carbonate (CaCO₃) precipitate.

This precipitate is harmless to human health, but not to that of your appliance. Over time, the build-up constricts the space where water is able to flow, forcing you to replace your dishwasher or plumbing.

To make matters worse, hard water also interferes with cleaning. For instance, the Ca2+ and Mg2+ ions interfere with the surfactant qualities of soap, which means you need to use more laundry or cleaning agents to finish the job properly.

Clothes laundered with hard water can get discolored by a mineral film and can turn stiff and scratchy. Due to the micro-abrasives in hard water, clothes may also fade more quickly and wear out faster.

Hard water can ruin your skin

Besides appliances and plumbing, hard water can also take a toll on skin and hair. When shampoo and soap come in contact with calcium and magnesium ions, the chemical reaction leaves a residue on your skin. Over time, this skin residue can clog up pores, which, in turn, can lead to acne and exacerbate skin conditions like eczema and dermatitis.

Hard water can also affect the skin on your scalp, making it dry and itchy. This is especially true for those with sensitive skin, such as those with psoriasis and eczema. For those with really sensitive skin, even laundering clothes in hard water can irritate the skin.

If you travel somewhere else for a week and notice a significant improvement in your skin, there’s a high chance that your water back home is to blame. In this case, fitting a good mineral filter for your faucet and showerhead is desirable.

How to tell if your water supply is hard or soft

• Water hardness test kits. You can directly test your water quality using a number of affordable options, from services that test for hundreds of substances, to simple dip-in, instant read strips.
• Warning signs. If you see white scaling on your faucets, if glasses come out of the dishwasher covered in cloudy film, or if you have trouble rinsing off soap and suffer chronic dry skin, you may have hard water.
• The soap test. This DIY test works wonders. Fill a glass halfway with water and add soap. Cover the top and give it ashake. If the glass has hard water, the water will be cloudy with minimal suds. If it’s soft, the water will be mostly clear, bu the top will be filled with bubbles.

In the end, hard water can lead to expensive repairs and can dramatically shorten appliance life. Hard water is great for drinking, whereas soft water is the better agent for other household uses.