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When considering which method of water treatment to adopt, there are many options being offered -  some seemingly more appealing than others, but it’s not quite so simple.


Some of the water treatment options you may have heard of are:


  • Chlorination / Bromination

  • Salt Chlorination

  • Ultra Violet Irradiation

  • Ozone Treatment Systems

  • Chlorine ‘Free’ Systems

Chlorination and Bromination


These are the chemicals that you will most likely have heard about, and there’s a good reason for that.  


Both chlorine and bromine sit in the same Halogen group within the periodic table, and offer excellent disinfection qualities, allowing a residual to be maintained within the water body (essentially providing the entire water body with the same level of disinfection at all times). 


This being said, some people have had bad experiences with chlorination, however this generally results from the incorrect maintenance of the pH or chlorine (or both).  If the required residual of chlorine is maintained (which differs between various types of water body, e.g., leisure pools, jacuzzis, hydrotherapy pools) within the correct pH parameters, then no such issues should arise.

Salt Chlorination


Salt chlorination systems still allow a residual of chlorine to be maintained within the water body, however this is provided by maintaining a residual of dissolved salt (sodium chloride), with the system electrolysing the dissolved salt into a ‘chlorine’ compound (generally Sodium Chloride to Hypochlorous Acid + Sodium Hypochlorite).  A benefit of this system is that is reduces the handling of  more harmful and hazardous chemicals, however with the increased salinity of the water, more careful consideration should be taken with the materials used within the pool shell and the filtration system due to the potential increased corrosion rate of materials.  

UV and Ozonation


Both commonly seen as secondary disinfection systems, for which they are both extremely effective.  Their issues lie with them not providing a residual of disinfectant throughout the water body, however these may be installed as a secondary disinfectant to chlorine, allowing a lower residual of chlorine to be maintained and often leading to much lower overall dosage of the primary disinfectant.


UV systems generally comprise of a full flow or bypass arrangement on the main water circulation system, with water passing through a chamber exposed to the UV irradiation.  The Ultraviolet element emits light of a certain wavelength which is very effective in penetrating the organic cell membranes, disrupting it’s DNA and thus preventing reproduction.


Ozone differs from UV however is often utilised for the same purpose of disinfection.  Ozone is inherently unstable and is the most powerful oxidiser that is commercially available (it does in fact provide greater disinfection properties than chlorine).

Chlorine ‘Free’ Systems


The first thought of many is that chlorine ‘free’ sounds appealing, and on the face of it I would agree.  A magical system that requires no chemicals would be ideal, right?  


Unfortunately there are problems associated with relying on a completely chlorine (or bromine) free system.  Firstly, the main benefit of chlorination is that it provides a residual level of disinfection throughout the water body.  Depending on the specific water body the required level of the residual chlorine content may vary, however the effect is the same. 


The most common systems that sell themselves as chlorine ‘free’, are silver/copper ionisers.  On paper, these looks great, however in my opinion there are a number of issues.


They do not provide the same residual protection that chlorine systems do (in fact you may see that for commercial systems they still have a requirement (generally in very small writing) to utilise an alternative residual disinfectant to remove the organic matter that the ionisation can’t). 


Another significant potential problem occurs with the ionisation between the cathode and sacrificial anode.  Over time (and not much time), the electrodes need to be replaced.  If the electrodes aren’t replaced then the electrolysis may occur between other metallic objects in the system, be it an electric heater, pump internals or even handrails.  This can lead to premature corrosion (in the best case scenario) and alternative electrical circuits (worse case).

pH Levels


Whilst the disinfection process is important, one extremely important factor that is ofter overlooked is the maintenance of correct pH levels within the water body.  The correct pH level is integral in ensuring that your disinfection works efficiently, and can vary between regions (mains water supply) and the specific water treatment method/chemical that you are using.  It is recommended that the pH level is maintained within a range between 7.2 to 7.8, with either the dosage of acid or alkali chemicals used to ensure that these parameters are maintained.

My Opinion


There are many factors which determine which water treatment system to adopt including bather load, water body type and budget etc.  If you were to ask me what my preferred water treatment method would be, it would always be based around chlorine as a primary disinfectant with UV or Ozone acting as an (excellent) secondary disinfectant.  I would tend to steer well away from chlorine ‘free’ systems.


If you have a swimming pool or project where you are thinking of installing a water treatment system, please feel free to get in touch and I will be happy to discuss what system may be best suited for you.

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