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Water-borne Disease Information for Health & Safety Executives

An Introduction to Copper-Silver Ionisation

‘If copper-silver ionisation is so effective, why aren’t I using it already?’

or, perhaps: 

‘Why haven’t I heard of copper-silver ionisation before?’

These are valid questions for which the answers will be found below.

As you will see from the information on this website, Tarn-Pure are the acknowledged experts in copper-silver ionisation in the UK, if not the world.

As with all systems to control ‘live’ water-borne bacteria, copper-silver ionisation works best with constant monitoring and testing.

Thus there are elemental aspects to copper-silver ionisation which dictate such criteria as:

  • where in the water-system it is installed
  • the physical accessibility of the system for regular servicing and testing
  • knowledge of water-flow rates
  • the hardness of the water, which determines the required Tarn-Pure product specification to minimise the inevitable calcification of the electrodes

Basic Background

There are many links on www.tarn-pure.com which testify to the clinical efficacy and effectiveness of copper silver ionisation. Because it has taken time to develop and refine, the following should be read as a basic introductory’ guide as to how the system works. 

Copper-silver ionisation works by passing an electric current through silver and copper electrodes immersed in a water stream.

This current causes the release of low levels of positively charged silver and copper ions into the water that is to be treated.

The rate of release of the ions is controlled by the amount of current delivered to the electrodes which, in turn, is controlled by the volume of water passing over a flow meter connected to the electronic control unit.

The positively charged silver and copper ions attach to negatively charged sites on the walls of bacteria cells, weakening and penetrating the cell membranes and killing the bacteria. 

The system also destroys the biofilm that accretes on the inside surface of water pipes which harbours, and thus facilitates, the proliferation of Legionella and other bacteria. 

This removes the life support for the bacteria and they die.

Unlike other more conventional water treatment systems, copper-silver ionisation provides long term residual disinfection as the ions can remain effective for long periods of time once they are released into the water.

The efficacy and operation of the sacrificial anodes (electrodes)

The silver and copper alloy electrodes installed in the Tarn-Pure Electrode Cell operate on the principle of cathodic protection – commonly adopted for corrosion control in process plant and pipelines across the world.

The electrodes inserted into the water stream are sacrificial anodes and, as the ions are released, these electrodes lose mass and deplete.

As ACoP L8 defines the requirements for silver and copper levels, it is simple to calculate the theoretical mean rate of depletion in order to maintain approved levels of silver and copper ions in treated water.

Silver ions are positively charged so have a propensity to recombine, or complex, with other negatively charged ions present in the water stream, most of which are chlorides.

When a silver ion comes into contact with a chloride ion it will immediately recombine into silver chloride and will drop out of solution.

This complex will fall to the bottom of the water pipe or tank and will present as an insoluble dust; and will be ineffective in attacking legionella bacteria.

This activity reduces the volume of silver ions available for treating the water, which is why Tarn-Pure sacrificial anodes are are adjusted to take complexing into account.

The additional silver must be introduced to the system to provide the overage which will be lost to recombination.

Tarn-Pure instals a patented titanium anti-scaling device within the body of the cell which inhibits scale accretion by a significant degree; but calcification cannot be completely eliminated unless the water is very soft.

When an electrode calcifies, the surface area available to emit ions is reduced, so depletion reduces at the same time.

Superficially, this can give the impression that the electrodes are lasting longer but the consequence is that ion levels may drop and become non-compliant.

This is why, as with chemicals, constant monitoring and testing is required. So, why isn’t copper-silver ionisation more commonly applied?

The honest answer is that, until now, the issues of erosion and calcification of the silver and copper electrodes in the ionisation cells has not been fully understood.

In 2012, as the market leader in this technology, Tarn-Pure has declared a corporate objective to:

i) Explain erosion and calcification more clearly, as evidenced by this website.

ii) Invest in innovative technologies to offer better control to our customers.

iii) Develop a more affordable, customer-friendly financial model.

We are, of course, happy to expand on all of these issues on a case-by-case basis.

The key reassurance and, we hope, the basis for any future discussion is the following extract from ACoP L8: 

Extract from Approved Code of Practice (ACoP L8)

The Health and Safety Commission approved on 23 November 1999 the Code of Practice entitled Legionnaires’ disease: the control of Legionella in bacteria in water systems (ISBN 0-7176-1772-6). Please find to follow an extract:


Ionisation is the term given to the electrolytic generation of copper and silver ions for use as a water treatment. Copper and silver ion concentrations maintained at 400µg/l and 40µg/l respectively can, if properly managed, be effective against planktonic Legionella in hot water systems. If however the water is softened, silver ion concentrations between 20-30µg/l can also be effective, provided a minimum concentration of 20µg/l is maintained. This level of silver still requires copper ions to complete the synergy.

The application if ionisation will need to be properly assessed, designed and maintained as part of an overall water treatment programme. The Water Supply (Water Quality) Regulations and Private Supply Regulations prescribe a maximum value for the level of copper and silver ions in drinking water supplies. It is important that installers of ionisation systems are aware of the need to avoid any breach of these regulations and maintain copper and silver levels below the maximum allowable concentration. The local water company may need to be consulted to check that the installation complies with the requirements of the Water Regulations.

It should be noted that in hard water systems, silver ion concentrations can be difficult to maintain due to build-up of scale on the electrodes, and the high concentration of dissolved solids precipitating the silver ions out of solution. For both hard and soft water, the ionisation process is pH sensitive and it is difficult to maintain silver ion concentrations above pH 7.6. The build-up of scale and concentration of dissolved solids therefore needs to be carefully controlled so that suitable ion levels are consistently maintained throughout the system. This may need extra water treatments.

For most systems, routine inspection and maintenance will usually be sufficient to ensure control (see paragraphs 180-182) if the following parameters are also monitored at regular intervals and remedial action taken when necessary, with details of all actions being recorded (see also paragraph 172):

(a)  the rate of release of copper and silver ions into the water supply; 

(b)  the silver ion concentrations at sentinel outlets should be checked monthly – this should be at least 20µg/l at outlets; 

(c)  the measurement of silver ion concentrations at representative taps selected on a rotational basis once each year – this should be at least 20µg/l at outlets; 

(d)  the condition and cleanliness of the electrodes; and 

(e)  the pH of the water supply. Please feel free to contact Tarn-Pure at any time.