What Is Water Hardness and What Are the Signs of Limescale?

The white crust that builds up in the bottom of the kettle, glasses that come out marked after a while, soap that will not foam in the shower and a boiler that fails earlier than expected… That picture is familiar in many homes and businesses, and the problems are usually taken to be unrelated. Yet behind all of them there is generally one common cause: the water’s high water hardness.

Those white limescale marks look unimportant at first, but over time they seriously affect both daily comfort and the life of equipment. So what exactly does it mean for water to be hard, what signs does it show, and is it really a problem? The answers lie in minerals we cannot see in the water.

What Is Water Hardness and What Does It Mean?

Water hardness expresses the concentration of mineral ions dissolved in water, above all calcium and magnesium. The higher the proportion of those minerals, the harder the water. Hardness does not mean the water is unhealthy; but it is a decisive measure when it comes to limescale build-up and equipment problems.

Hard water, also called “limey water” in everyday speech, is really water rich in minerals. The basic issue is that those minerals leave solid residue on surfaces with heat and evaporation. Water hardness cannot be seen directly, but it makes its effects clearly felt on taps, in appliances and in the plumbing. It is therefore better to think of hardness not as “bad water” but as a property that has to be managed.

Why Does Water Become Hard? The Role of Calcium and Magnesium

As water moves underground it passes through rocks such as limestone and dolomite, and in doing so it dissolves calcium and magnesium ions and takes them up. Where the geology of an area is rich in limestone, the mains water is naturally harder. Hardness therefore varies markedly from area to area.

Once they are in the water, calcium and magnesium lose their solubility when heated and turn into solid calcium carbonate — the limescale we know. That is why limescale builds up most on heated surfaces: in the bottom of a kettle, in a boiler heat exchanger and in electric heaters. The reason two neighbours in the same area can have different experiences of hardness is usually that difference in minerals at the mains source.

How Are the Signs of Hard Water Recognised at Home and at Work?

The signs of hard water are generally visible: white limescale marks on taps and fittings, residue on glasses and in the kettle, soap that will not foam easily, a dry feeling on the skin and a fall in the performance of white goods. Where these signs appear together, the hardness level of the water is most likely high.

Taken one by one these signs look small, but assessed together they form a clear picture. The most common signs of hard water are these:

• Stubborn white limescale marks on taps, fittings and shower heads
• Sediment and marks left on glasses, plates and in the kettle
• Soap and detergent that will not foam easily, and more product used
• Laundry going stiff and colours dulling over time
• A dry feeling on the skin and a lifeless feel to the hair
• A noticeable change in the taste of tea and coffee

What Effect Does Hard Water Have on Appliances and Plumbing?

Hard water deposits limescale in every appliance that heats and lowers efficiency. A blocked heat exchanger in a boiler or water heater, a failed heating element in a washing machine or dishwasher, and lost energy in heating systems are the most common results. Because the limescale that builds up blocks heat transfer, appliances use more energy and wear out earlier.

A layer of limescale behaves like insulation; that means the heater has to work harder to heat the water. As a result the energy bill rises and the life of the appliance shortens. The higher the water hardness, the faster limescale builds up in appliances. Heat-producing equipment such as boilers, water heaters, storage heaters and white goods are the parts most affected by a limescale problem.

In businesses the picture is more critical still: limescale build-up in steam boilers, heating lines and industrial equipment directly raises maintenance costs, energy consumption and downtime. In that sense a limescale problem is not only a matter of comfort but a concrete item of operating cost.

Figure 1: Limescale build-up on taps and appliances caused by hard water

How Is Water Hardness Measured? Fr, dH and TDS

Water hardness is generally measured in French degrees (°Fr) or German degrees (°dH). 1 °Fr corresponds to roughly 10 mg of calcium carbonate per litre. TDS shows the total dissolved solids in water; it is related to hardness but is not the same thing.

In a practical classification, water is grouped as soft, moderately hard and hard. By general agreement, low °Fr values indicate soft water and high values hard water. The most practical way to learn the water hardness level at home is a simple hardness test kit or an authorised water analysis. In measuring water hardness, therefore, the amounts of calcium and magnesium are what count.

Another important distinction is not to confuse TDS with hardness. TDS also covers ions such as sodium and chloride that contribute nothing to hardness, so a high TDS does not always mean high hardness. To establish hardness clearly, a measurement focused on calcium and magnesium should be preferred.

Does Hard Water Affect Health?

Because of the calcium and magnesium it contains, hard water generally poses no health risk for drinking; those minerals are necessary for the body. In assessing drinking water quality, the World Health Organization likewise does not define hardness as a health threat in itself. The real issue lies not in health but in the technical effects of limescale build-up.

Accepted as the authority on the subject, the World Health Organization’s assessments of drinking water qualitystress the importance of access to safe and clean water while not putting hardness forward as a basic health parameter. That said, hard water can have effects on comfort, such as dryness of the skin or a lifeless feel to the hair. These are less a medical complaint than the way the mineral concentration of the water shows in daily use. In short, the main disadvantage of hard water is not health but its effect on appliances, plumbing, energy consumption and comfort at home.

Figure 2: Solving the limescale problem at source with water softening

A Lasting Answer to Limescale: How Does Water Softening Help?

The most lasting answer to a limescale problem is to soften the water and reduce the hardness at source. Water softening systems remove calcium and magnesium ions from the water by ion exchange. Limescale is thereby largely prevented, appliances are protected and daily comfort with water rises markedly.

Temporary answers — descalers, frequent cleaning or single filter changes — ease the symptoms for a while but do not remove the cause. A lasting result calls for systems that lower the hardness of the water at the inlet. Water softening systemsprovide softened water to the whole plumbing system, both extending the life of appliances and bringing a noticeable ease to daily use in the shower, the dishwashing and the laundry.

To choose the right system you first need to know the degree of hardness and the daily water consumption. Where a separate quality is aimed for in kitchen and drinking water, domestic and office water purifiers can be considered alongside the limescale solution. That way the plumbing is protected against limescale and the quality of the water you drink can be raised.

Frequently Asked Questions