Water Conditioning

What is a water conditioner?

The term water conditioner (sometimes called physical water conditioner or physical water treatment device) is generally used to describe a wide range of products that are designed to prevent lime-scale build-up on heat-exchange surfaces when hard water is heated. Unlike softeners or filters which work by removing the ions (hardness salts) which form the lime-scale, water conditioners generally work by affecting the chemistry of the precipitation reaction: suppressing lime-scale formation, reducing the rate of scaling, or by altering the form of the scale or the chemistry of the precipitation mechanism itself. There are lots of different types of products on the market with a variety of claimed operating mechanisms.


The most common types of water conditioner include:

  • Magnetic – Claimed to prevent scale-build-up by influencing the type of lime-scale crystals precipitated – causing more needle-like aragonite crystals to be formed, which find it harder to stick to heat-exchange surfaces, than the normal calcite, which forms harder surface deposits. Laboratory research has shown that the growth of lime-scale crystals in a saturated solution is affected by the application of an external magnetic field.
  • Electrolytic – Work by adding a small trace of zinc (sometimes iron) to the water which has the effect of suppressing lime-scale formation and providing nucleation sites (seed crystals) where precipitation occurs which is washed away by the water flow. Laboratory research has shown a relationship between the amount of zinc added and the reduction in lime-scale precipitation achieved.
  • Electronic (Electromagnetic) – Generally claimed to work by causing dissolved hardness salts to cluster together to form nucleation sites for lime-scale precipitation rather than forming on heat-exchange surfaces.
  • Electro-chemical – Currently mostly of German or Austrian origin - Usually containing some type of cartridge filled with ceramic beads which are claimed to cause some the dissolved calcium and magnesium ions to precipitate as seed crystals which then act as nucleation sites for bulk lime-scale formation when the water is heated. Often quite large in size and requiring a mains power supply.
  • Electrostatic – Claimed to use the build-up of static electricity derived from the water flow to enhance the nucleation of seed sites for lime-scale precipitation.

Why fit one?

The UKWTA has demonstrated how lime-scale build-up has a major impact on reducing the efficiency of domestic water heating appliances – so much so that lobbying the Government has now resulted in a change in the UK Building Regulations (the Domestic Heating Compliance Guide - published May 2006) to require treatment of the feed water to water heaters in hard water areas to inhibit lime-scale formation.

The benefits of installing a water conditioner can include:

  • Reduction in heating costs by maintaining the efficiency of water heating appliances
  • Reduced scale deposits around taps
  • Easier removal of lime-scale from kettles
  • Easier cleaning of surfaces, shower–heads and cubicles where lime-scale might normally build-up

Which water conditioner is right for me?

It is generally understood that water conditioners are not completely effective in preventing lime-scale build-up – they reduce scale build-up by modifying the form of the scale produced making it less likely to stick heat-exchange surfaces. Although there are claims that certain products are ineffective in comparison with other technologies, there is significant evidence that most are generally beneficial with many modern products providing a very high level of satisfaction. Unfortunately, wild claims by less scrupulous manufacturers in the past have led to some reluctance to recognise the ability of water conditioners, although the publication of field test results by authoritative bodies, and the introduction of performance warranties for some products, is increasing confidence. Performance is dependent on initial water quality and may be influenced by the installation practice, for example some manufacturers advise against positioning near tee-off points to household appliances as this may lessen the treatment effect. It is essential to seek advice from the manufacturer or retailer and to follow the installation instructions carefully.

What should I do?

Work with a reputable manufacturer or dealer who can help guide you through the various technologies – Begin by consulting the list of UKWTA members.