Hard and soft water

When understanding hard water, we must first begin with something that all of us here in the British Isles are all too familiar with. Rain.

We always complain about the rain, but it is a part of our national character, a result of both our location on the globe and the constant process of the water cycle.

To recap, the water cycle is the process that creates rainfall and hard water. To summarise, the sun heats water, which in turn evaporates into water vapour. Water vapour rising into the air, where it eventually cools and condenses into clouds. The clouds will be transported long distances and will eventually break apart forming precipitation or rainfall. Water collects on the ground, rivers, lakes and oceans, where the sun will heat it up once again, starting the process all over again.

Hydrological cycle Rainfall is naturally soft. Water is hardened by percolating through layers of earth and rocks before its inception and treatment to become tapwater.

When it is falling, rainfall is soft containing acid. It is only when it hits the ground and starts percolating through the rock it will come into contact with chalk or limestone. These will then dissolve and will be picked up by the water. As a result hard water is created.

To clarify:

What are the effects of Hard Water?

Hard water’s primary benefit is its function as decent drinking water, containing all those vital minerals that will make the body stronger. The minerals determining it’s ‘hardness’ is what gives water the closest thing it has to a taste.

The negative effects of hard water come in the deposition of scale and scum. You may be familiar with the telltale signs. Tidemarks around baths and basins, unsightly white marks on sinks, toilet bowls and shower heads. In worst case scenarios the build up of this material can create blockages in pipework and lead to the premature failure of water heaters.

Due to its composition, hard water has difficulty making a lather when combined with soap, resulting in a less than effective wash. Clothes can be left grey and dingy, whilst dishes and glasses can appear dull and smeared. It can really affect the longevity of your clothes and cutlery.

Hard water is less suitable for washing, as its rich mineral makeup prohibits an effective reaction with soap. This basically means that it is harder to create lather, foam and bubbles with hard water resulting in a less than effective clean.

Water hardness in the UK

England and Wales water hardness - calcium carbonate levels Map showing water hardness in mg/l as Calcium Carbonate in England and Wales. Source: Drinking Water Inspectorate. Collated 2009.

Hard water is widespread across the entire UK, though some places have a richer composition than others.

To give you a better sense of the presence of hard water in the UK, this map provides a more accurate overview.

As you can see, Wales and both North West and South West regions have the softest water, whilst most of the UK is host to hard water. It should also be noted that Northern Ireland and Scotland are naturally soft.


There are many ways in which water hardness is measured. In the following table we have displayed how water hardness is measured further afield.

Hardness can also be measured in parts per million (ppm). 1 mg/l = 1 ppm.

Different units of hardness and their equivalent values.

mg/l or ppm as calcium carbonate equivalent mg/l calcium Degrees Clark or English Degrees German Degrees French Grains per US gallon mg/l of sodium added during softening**
100 40 7 5.6 10 5.8 46
200 80 14 11.2 20 11.6 92
300 120 21 16.8 30 17.4 138
400 160 28 22.4 40 23.2 194
435 174 30.5 24.4 43.5 25.2 200*
* Maximum sodium concentration in Water Regulations
** For total sodium concentration add the amount of sodium present in the mains water supply - information that can be obtained from your water supply company.

Hardness by postcode

Type in your postcode and find out the exact hardness of water in your area through our handy tool.

Water softening

Water softening refers to the process in which the calcium and magnesium minerals are removed from hard water to create softened water.

It can be performed by a water softener, a device that connects to your plumbing system, ideally at an easy access point - under your kitchen sink, for example. Water softening is a two part process comprising of ion exchange, in which the mineral content is drawn out through salt percolating through resin beads, and a regeneration stage in which the minerals are flushed from the system.

The result is softened water and all the benefits this entails.

Benefits of softened water

There are many benefits to softening water, it improves the longevity of appliances, leads to substantial cost savings through lowering usage of cleaning products and soaps and is incredibly good for skin and hair.

  • Greater economy and cost effectiveness softened water will reduce the cost of maintenance and replacement of water heaters, dishwashers, washing machines and showers by extending their life. Each year, in a hard water area (300ppm as calcium carbonate equivalent) the average family home will use water containing 70kg (154lbs) of scale. Unchecked, it will cause damage and expense. It is estimated that an ion-exchange water softener could save in the region of £400 for this average 4-person household.
  • Improves the efficiency of your boiler At the end of last year, it was announced that fuel bills were expected to rise by 9%, but softened water can boost heating efficiency. Hard water, by comparison leads to scale buildup, just a mere 1.6mm of build up will lead to a 12% loss in heating efficiency. Scale is one of the major threats to boilers that can lead to significant maintenance costs and inevitable replacement. A boiler running with softened water will have a greater lifespan of up to 15 years.

Health and lifestyle benefits

  • Improves the effect of cleaning products Softened water can save some 50% of washing powder and toilet soap consumption, reducing the amount of shampoos, conditioners and cleaning products used.
  • Time savings Washing the dishes is often regarded by some as a chore, but because softened water makes washing so much more efficient, the time actually spent actually washing is greatly reduced.
  • See the results of better washing Softened water rinses completely away without leaving scum, even after shaving. Softened water makes laundry brighter and glasses sparkle and shine. Softened water makes washing the car easier, reducing streaking and spotting. Softened water makes hair soft and easy to manage.
  • Health benefits Provides aid for dry skin conditions - such as eczema.
  • See the results of better washing Softened water rinses completely away without leaving scum, even after shaving. Softened water makes laundry brighter and glasses sparkle and shine. Softened water makes washing the car easier, reducing streaking and spotting. Softened water makes hair soft and easy to manage.
  • Enhance the stress relieving power of a good bath! Bathtime becomes a luxury, as softened water has a clean silky feeling without the need for bath oils or bubble bath liquids.

How does a water softener work?

How water softeners work Twin tank water softeners provide a continuous supply of softened water, as one cylinder regenerates as the other is in use.

So how does water softening work? Domestic water softeners have been in circulation in UK homes for quite some time now. There are many different kinds.

Water softening is based on a process called ion exchange, in which calcium and magnesium ions are exchanged with sodium chloride (salt) via a special resin.

As you can see from the diagram the hard water goes into the pressure vessel where it moves through the resin beads where the calcium and magnesium are replaced by sodium. This is how exchange takes place and softened water is the result.

Single versus double cylinder water softeners

Non-electric versus electric

Water Softeners typically come in either single cylinder variety or the twin cylinder type. When you require a large amount of softened water, perhaps for a big wash after a family meal, you will find the single cylinder system trouble keeping up with demand. The softening process is a two stage process involving the separation of the calcium and magnesium ions followed by their removal through the regeneration process. When single cylinder systems are forced to treat large amounts of water the regeneration process has trouble keeping up. Usually the regeneration process is triggered by an electrical timer, which regenerates the system when it is not typically in use (during the night or the working day for example). The result, is that hard water will flow from your taps and the regeneration system may take 4-5 days to complete and it will waste water and salt in the process. Twin cylinder water softeners work off pressure and can regenerate continuously.

The general differences between the two softeners are:

Twin cylinders Single cylinders
Easy to Install. Small size takes up little space. Single cylinder systems provides a degree of automation to measure and start the regeneration process and require an electrical supply.
Powered purely by incoming water pressure. Doesn’t affect monthly electrical bills. Does require electrictricity to power the timer.
Few moving parts, no electrical components means low maintenance costs. More moving parts and electrical components - higher maintenance costs should things go potentially wrong.
Two cylinders can process more softened water for up to 10 people. Since it can regenerate constantly, you will never get hard water into your system. When large quantities of hard water go into the system for treatment, single cylinders can find difficulty in regenerating to keep up with demand. This means that hard water can get through the system.
Just add salt! No fiddly controls, simply keep the system topped up with salt blocks. Requires a degree of training and setup to interface with correctly.
May require an annual service
A water softener in situ in a kitchen, under the kitchen sink


For more frequently asked questions please go to our FAQ section.

About the author

Written by Harvey Bowden, Chairman of Harvey Water Softeners Harvey Bowden Chairman at Harvey Water Softeners

Having worked in plumbing and central heating, founded Harvey Water Softeners in 1978. He launched the twin cylinder non electrical under the sink water softener in 1981, which went on to become the best selling water softener in the UK. Over the years as the market grew, he developed the technology further, introducing block salt to the process in 1995 before coming up with his own water softener in 2001. To this day, his water softeners are designed and manufactured exclusively within the UK.