Ozone is a sky-blue gas and is formed naturally by the action of the suns UV (ultraviolet) rays splitting an oxygen molecule (O2) and one individual oxygen atom attaching itself to another oxygen molecule. This is ozone and is expressed as O3. It can also be formed when a large electrical discharge passes through oxygen.(eg. lightening). It is a relatively unstable, highly toxic gas which decomposes to re-form oxygen and is a very effective bactericide.


Ozone generators produce the gas by one of two methods; Ultra Violet Light or Carona Discharge.

Ultraviolet light (UV)

Generation of ozone using UV is achieved by passing air over a UV light source and then mixing the gas with water.

Carona discharge

In this method, air is passed through an electrically charged chamber. What could be called a miniature lightning storm is created in the chamber which electrically converts the oxygen into ozone.

Note: The concentration of gas produced in both types of systems can vary and care should be taken when selecting a unit to be sure that ozone output is appropriate for your pool or spa.


No Ozone treatment has been used for many years, particularly in Europe, for the treatment of municipal water supplies and also large commercial and Olympic pools. Developments in ozone technology over recent years has enabled manufacturers to produce smaller more economical generators, much more suitable for domestic pools and spas.


Ozone is one of the most effective disinfectants and oxidisers available and once introduced into the water it starts to work immediately, killing bacteria and oxidising organic waste. As ozone is not highly soluble in water, the ozone must be injected into the water by either a compressor or venturi system.

However, as ozone is also toxic, all traces must be used or removed prior to reaching the pool. As there can be no residual of ozone, some other form of residual sanitiser like chlorine or bromine must also be used in order to provide continuous protection when the ozone generator is turned off.

Naturally, using ozone as the primary oxidiser, means a much smaller amount of chemicals will be needed to sanitise the pool and provide the necessary residual.


When using an ozonator in pools and spas treated with chlorine, always follow the manufacturers recommendations on maintaining pH.

In pools treated with ozone and bromine, the oxidising power of ozone will regenerate the inactive bromine, reducing the consumption of bromine product.

Ozone remains in the water for only a short time and therefore has no effect on pH or water balance, nor does it contribute to Total Dissolved Solids.

The use of a correctly sized and operated ozone generator with a pool disinfecting chemical (eg. chlorine), will keep a pool clean and reduce the need for shock dosing.



The use of ozone to disinfect swimming pools and spas has been a common practice in Europe for over 50 years. In the past five years, the United States pool and spa industry has become increasingly interested in ozone as a supplemental disinfectant to traditional chlorine and bromine-based water treatment. The reasons behind this include a need to provide exceptional water clarity with minimum chlorine odor and bather discomfort, and the recent media coverage regarding chlorine resistant pathogenic parasites (Cryptosporidium parvum) and bacteria (Legionella pneumophila) that exist within many municipal water systems. Ozone is now used as a disinfectant in the Margaret Bell Pool at the University of Michigan (U-M).


Applicable Regulations
National Sanitation Foundation Standard #50.

State of Michigan Act 368 Part 125.


Overview of Procedure
The use of an ozonation system that is properly sized and integrated into the swimming pool treatment system will allow ozone to act as the primary oxidizer and disinfectant. Ozone is fed into the pool feed water prior to the chlorine injection process. Ozone destroys many organic compounds and microorganisms that would typically react with chlorine, resulting in a reduction of the chlorine demand and total dissolved solids. Lower chlorine demand allows the pool operator to achieve disinfection of the water with minimal chlorine residual, and the reduction of total dissolved solids improves the water clarity. The reduction of chlorine usage will minimize the amount of chlorine off-gas that causes corrosion in swimming pool environments. Ozone will also break down chloramines, a major cause of the odor and eye irritation associated with swimming pools.


Waste Minimization Procedure
At the Margaret Bell Pool, an ultraviolet bulb ozone generating system is mounted in the pool mechanical room. Ozone generated by the system is mixed with recirculated pool water and pumped through tubing to a 1,200 gallon surge tank. Contact time in the tank is approximately 5 - 10 minutes. The water is sent through a filtering process, chlorinated, and returned to the pool. It is expected that a reduction of chlorine use will be realized; however, the ozonation system has been in place for only a short amount of time, and quantitative data detailing actual chlorine usage has not been obtained. This section will be updated as information becomes available. 


Known Limitations
None known.


Safety & Health Precautions/Personal Protective Equipment
Follow all applicable safety and health protocols and regulations as established by your institution.


The addition of ozone to the swimming pool treatment system will provide better water quality for the swimmers, including a reduction of the chlorine odor and eye irritation, and improvement of the water clarity as a result of the reduction of the total dissolved solids.

Additionally, a reduction in chlorine usage is expected as a result of the ozonation of the swimming pool water.


A disadvantage to using ozone, especially for pool maintenance personnel with an existing respiratory condition, would be the presence of slight amounts of ozone in the air potentially contributing to health related problems.





1.    Chlorine reacts with organic waste and forms a large number of highly toxic chloro-organic compounds, also referred to as combined chlorine. These are well known carcinogens, and are also very poisonous to marine life. In swimming pools these toxins may accumulate to very high concentrations. Red eyes and rashes are the most instant and obvious effects, and should be considered signals of a much more serious risk to human health. Pools usually use makeup water to dilute these dangerous compounds. As a result, an equal amount of pool water must be released into the environment.

PUBLIC POOL2.     Ozone systems are available to assist flocculation of organic waste at the overflow pond prior to filtration. In these systems ozone removes as much organic waste as possible thus leaving less waste for chlorine (bromine) to react with. The target level of combined chlorine is not to exceed 1.5 ppm. Bromine is more suitable than chlorine for cooperation with ozone.

While this is a very significant improvement, on average, the human body will absorb about half a liter of pool water every hour. The best pools have their water quality in compliance with the standards for drinking water supplies.

3.    There are more then 30,000 swimming pools in Europe treated with ozone. In North American pools, the ozone dosage has often been underrated and a proof of ozone output was usually not required. Some ozone suppliers will then claim that chlorine is needed anyway and use this as an excuse. In the past this has caused understandable mistrust and this explains why the use of ozone in North America is at least 30 years behind Europe.

4.    In Canada, B.C. Pool Regulations (Section 75) require that "a suitable residual of disinfectant shall be maintained throughout the swimming pool water". Section 47 further states: "If means other then chlorine are used as a disinfectant, residuals of equivalent disinfecting strength shall be maintained in the pool water in accordance with Section 75." Yet, Some health inspectors and most surprisingly — some engineering consultants continue to claim that a chlorine residual must be used. This is probably the result of a long-time misconception that ozone is too unstable to provide sufficient residual. In truth this is all a matter of dosage and water distribution within the pool.

5.    Where the water distribution is to the latest building code, and the turnover time is below six hours, freshly charged water will reach every spot in the pool in less than five minutes. The halflife of ozone in water is 15 to 20 minutes. The best way to prove ozone’s effectiveness is by measuring the ozone residual returning from the pool. It should read at least 0.05 mg/L. The maximum allowable in Europe is 0.15 mg/L. Our systems monitor the dissolved ozone in the return from the pool, and just prior to further ozonation.

Some questions have been raised as to whether dissolved ozone is toxic to humans. No toxicity was observed for exposures of over 8 hours at levels of 0.15 mg/L of dissolved ozone. It is absolutely certain that dissolved ozone is by far less toxic than equivalent levels of chlorine or bromine.

6.     Bromine, ozone and hydrogen peroxide have been used successfully in the past with or without chlorine residual. Ozone is the strongest and most convenient disinfectant of all. Its stability in water is most convenient and it appears to be ideal. Present technology allows simple, automatic maintenance of the appropriate ozone residual level.

INDOOR PUBLIC POOL7.    There are many advantages of treating pool water with ozone:

• Filtration support. Ozone assists flocculation of organic waste materials, thus enhancing the effectiveness of sand filters.

• Water purification. Ozone directly decomposes organic waste by oxidation.

• Water sanitation. Properly dissolved ozone residual of 0.05 mg/L or higher assures a 100% kill of all bacteria, viruses and fungus.

• Water ozonation. Unused ozone slowly decomposes to normal oxygen and remains dissolved in the water to the point of saturation. This makes the pool water clean, sparkling and appealing.

• Leaves no toxic residues in the treated water.

• Ozone is produced on site and does not require storage or transportation.

• Dissolved ozone at levels below 0.15 mg/L do not cause adverse health effects even during long term exposure.

• Undissolved ozone off-gas is easy to separate from treated water in the off-gas tank, long before entering the pool, while chlorine is being constantly released in its highly toxic gas form right above the pool water.

• Ozone ends water discharge liabilities.

• Ozone prevents calcium carbonate scaling, removes existing scale, cleans and prevents greasy sediments on pool sides. Ozone treated water has a much lower cleaning cost.

8.    Chlorine is controversial

Some older engineering specifications for Ozonation systems may still require that "all ozone is destroyed prior to entering the pool by passing through a carbon bed, then chlorine is introduced instead to maintain a disinfecting residual". Such requirements are partially based on a 30 years old German DIN procedure, an archiac design which has been changed. Reliable off-gas systems are now able to strip all undissolved ozone gas from the water flow safely thus no free ozone gas can escape to the pool. In the meantime, fear of ozone has diminished thanks to hundreds of published scientific studies. Ozone has become known as being of major health benefit to swimming pool users, and is being used by countless hospitals and rehabilitation centres. Today's technology does not always require chlorine assistance, except as a backup in case of maintenance or power blackout.

Using bromine (or chlorine) residual may be more acceptable where economics do not allow the best solution. In such cases, AZCO's modular system allows for easy expansion at a later date when the funds become available. Bromine is much more suitable than chlorine where there is a need to complement an ozone system (bromine cooperates with ozone chemically). While bromine is more expensive to buy, much less bromine is needed since ozone will recycle bromine up to 14 times in the pool water.

PUBLIC POOL9.    AZCO's own research has been verified at a number of public, commercial and hospital pools. The dosage in most cases is only 0.25 grams of Ozone per m3 (or 1 gram per 1000 gallons) of pool volume. A typical former German Engineering specification would require only about one third of this amount of ozone. But together with some extra carbon filters, large mixing and contact tanks and considerable space demand, the total cost of an old German system may easily end to be 2 to 5 times higher. Even for this much money the bathers are still treated with chlorine. Chlorine-free pools have been in operation for over 50 years in many non-German speaking countries as well — especially in France.

10.  During ozone start up in pools where chlorine was previously used, ozone may cause a few hours of foaming, flocculation, and milky water color. These are proper oxidation processes, carried out in a one-time event with no harmful effects. The filtration system will remove the oxidation byproducts and the water will become sparkling clean and sky-blue with a pleasantly clean smell.

11.  All AZCO installations are approved by the health authorities and Worker's Compensation Boards, where applicable.

12.  AZCO's ozone generators provide all the necessary ozonation power to purify, ozonize, and sanitize swimming pools, whirlpools, ponds, water works, and lakes of any size. The production of ozone is automatically maintained at the desirable levels anywhere in the whole pool. AZCO's modular system provides spare capacity in case of failure of any part of the ozonation system. Chlorine backup will be automatically employed in the unlikely case of extreme overload.


There are seldom two identical swimming pools or spas in the world. AZCO's engineers are ready to review and utilize your pool(s), existing equipment (such as tanks, pumps, filters, buildings) to be fitted for ozonation. To do so most efficiently, please answer the attached questionnaire. Your answers will be kept in strict confidence. The systems are engineered for fully automatic and worry free operation. Many features are included to prevent an overdose of ozone. Any single failure will not result in any increased risk for the bathers.

Ozone generators must be installed in a well-ventilated and dust-free room. In most cases, only a few square feet of floor space is needed. Detailed instructions for installation and operation will be provided when the project is ordered. The systems are easy to operate and maintain. The overall warranty is for three years, except on pumps where the manufacturer’s warranty is applied (generally one year).

Please call our Engineering Department at 604-596-0282 or fax to 604-599-4668 if you have any questions. Over five thousand AZCO systems have been installed on various water/air treatment projects, such as swimming pools, community drinking water systems, wastewater, aquacultural implementations, and many more. References are available.