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What is limescale?

Updated: Jun 3, 2020

Limescale build-up on a showerhead
Limescale build-up on a showerhead

PHOTO CREDIT: by Graeme Maclean via Flickr under this CreativeCommons license

You’ve probably heard this word many times in the past, especially if you live in an area that has hard domestic water supplies. But do you know what it means?

Before we talk about limescale, we’ll have to know a bit about hard and soft water. There are other articles in The Reservoir, our Professional Knowledge Database, about hard and soft water so we won’t go into any more detail than to say that you’ll have limescale if you’ve got hard water.

Limescale in the home

If you didn’t know previously, you should now realise that hard water contains calcium and magnesium minerals in solution. Normally these are quite safe and won’t hurt anyone or anything. However, the dissolved minerals easily drop out of solution if you add heat or allow them to take part in a chemical reaction.

Don’t worry, you’re not back at school and you won’t be tested on the information you’ll learn today. But, if you read on, you’ll get some basic chemistry and understand how limescale turns up in your water system.

The science bit

Hard water contains calcium and magnesium carbonate, bicarbonate, chloride and sulphate, all of which are soluble in water. Carbonates and bicarbonates cause temporary water hardness and can be removed by heating the water or by adding water softeners. Chlorides and sulphates cause permanent water hardness and can only be removed by chemical reactions with water softeners or in an ion-exchange column.

So, what is limescale?

Limescale forms when soluble calcium bicarbonate decomposes with heat to form insoluble calcium carbonate. You’ll also find that the calcium bicarbonate reacts with stearate compounds in soap to form scum.

Where do we usually find limescale?

Unfortunately, limescale isn’t a pleasant thing to see around the home. It makes kitchens and bathrooms unsightly and gives the impression that you haven’t cleaned.

Furthermore, no matter how unsightly limescale seems, that’s not the most important problem. Limescale accumulates in your kitchen and bathroom appliances that are in contact with water. Appliances such as the washing machine, dishwasher, and kettle. It doesn’t stop there though. Limescale also builds up inside water heaters, inside water pipes (especially hot water), and on taps in the bathtub, washbasin and sink.

Shall we add a few more places too?

Shower heads slowly clog until they stop working and you’ve limescale smears in bathtubs and toilet bowls. Limescale slowly blocks your central heating radiators too, if they’re not regularly flushed through.

That’s a pretty frightening list of places to find limescale, isn’t it?

Limescale build-up on a water tap
Limescale build-up on water taps

PHOTO CREDIT: by Petras Gagilas via Flickr under this CreativeCommons license

What does limescale do?

Apart from looking unpleasant, limescale affects many parts of your home and in fact impinges on your health too.

Limescale affects your domestic water system

If you could look inside your hot water tank you would see a dirty white material coating the heating element and tank interior. This is where the minerals deposit due to heat. In fact, if you look inside your kettle you’ll see the same phenomenon coating the element and interior. Sometimes you’ll see white streaks running down the outside of the spout as well, just the same as your taps. Limescale around a heating element, believe it or not, reduces the efficiency of the heater, resulting in higher utility bills.

Limescale doesn’t only collect in kettles and other water heaters. It also lines the inside of water pipes, especially the hot ones. As the limescale slowly builds up, the pipe diameter reduces thus reducing the water flowrate to the tap.

You may have seen a crusty substance on your shower head, possibly partially blocking the spray holes. That’s limescale too, but because the holes are so small it won’t be long before they clog up completely, rendering it useless.

Limescale on a heating element
Limescale on a heating element

Now let’s talk about health and wellbeing

Hard water in itself won’t hurt if you swallow it. It’s not poisonous or anything like that.

But… if you wash with it, it can change the way your body reacts to soaps, shampoos and worse, micro-organisms.

Soaps & shampoos

Let’s talk about soaps and shampoos first. As mentioned earlier if you use soaps in hard water, you’ll form a scum around the bathtub or sink. The scum, however, doesn’t only form there, it also coats your skin and hair too. In fact, you’ll find you must use more soap to produce a lather and then rinse more often. If not, your skin pores become clogged leading to skin problems and your hair becomes lank and lifeless as well as having an itchy scalp. Limescale is definitely bad for your hair and skin and, If you already suffer from eczema you’ll find you really have a problem.


But, that’s not all. Your skin naturally produces oils that keep your skin slightly acidic. This helps prevent fungi and bacteria from gaining a ‘toe-hold’ and multiplying. Hard water is alkaline and neutralizes your acidic barrier, allowing those nasty microorganisms to invade.

There’s one more type of disease of which you should be aware if you store water and especially if limescale is present.


Legionella bacteria
Legionella bacteria - grow in warm still water

Have you heard of Legionella? It’s a bacteria that likes nothing more than to grow in warm still water. Something like your hot water tank or standing-water in pipes at room temperature. It thrives between 20°C and 45°C but dies above 60°C, so keep your hot water above this temperature. A smooth surface usually prevents it from gaining a hold so if you have modern plastic water tanks and soft water then you should be ok. If you have limescale coated surfaces however, you’ll have all the nooks and crannies that Legionella loves to inhabit.

Luckily, you can’t catch Legionella from washing or drinking infected water. It only invades your body if you inhale small droplets and has symptoms like pneumonia or influenza.

Although it’s not very common to catch Legionella from your domestic water system, it is more likely if you have hard water, use a shower or cause spray from running a tap and allow the water to stand for long periods of time. For example, when you go away on holiday for a week or two. On your return, allow the water in your system to run for a few minutes. This will remove any stagnant water that might be infected

Limescale prevention

The obvious way to prevent limescale is to condition your domestic water as it enters the house. You can use an ion-exchange column to remove the calcium and magnesium from the water.

Luckily washing machines and dishwashers already have ion exchange columns built-in and they only need to be topped up with water softener. That only leaves water heaters, taps and showerheads.

If your domestic water supply is hard, you’ll need to prevent scale accumulating within the pipes. You can do this by a periodic flush. See a plumber if you need to organise this.

Taps can be easily cleaned by wiping with a solution of white vinegar and water to remove scale from the outside. Likewise, showerheads must be cleaned too. An easy way is to remove the spray attachment and soak it in a white vinegar solution overnight. This always works because the acid dissolves the limescale sediments.

Another way to sort out your shower head is to fit one that not only filters the water but also removes hardness. The StoneStream EcoPower Shower Head filters most waterborne particles from your shower water. You can also fit a Universal Shower Hard Water Filter, which will remove particles, limescale, bacteria, chlorine and more.

Sounds like a no-brainer!

So, you see there’s no reason to put up with hard water, limescale and all the problems they bring. If fitting a water conditioner to your supply is too expensive, then at least fit a suitable showerhead and hard water filter. Your kitchen and bathroom will look cleaner and brighter and you’ll feel cleaner when you reduce the bacterial problems associated with limescale.

Go for it!

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