Chlorine or UV-C pool sanitizers: which kills the most swimming pool bacteria?

To clean a pool, water is taken from the pool and filtered. Right? Well, that is just part of the solution… a clean pool, spa or hot tub is both visibly and invisibly clean, which means: no viruses, no molds and no bacteria that are hazardous to the health of swimmers.

To secure the health of the end user, reducing swimming pool bacteria is definitely a must when selling pool sanitizers. This article gives you some insight on the main causes, risks and effective killers of swimming pool bacteria. And that might as well improve the health of your business too...

What causes those dangerous pathogens to enter the water in the first place?

  • Pets and wildlife, mostly an issue with outdoor pools
  • Bacteria that are carried by bathers and swimmers (for example in saliva and on the skin) which dissolve into the water

There are some factors that increase the forming of micro-organisms in the pool. Heating up the pool for the swimmer’s comfort accelerates the forming of micro-organisms, including the hazardous ones. Also, a poor water circulation in the pool can make it difficult for all pathogens to be inactivated because the pool sanitizers can’t reach them.

Unfortunately, the above mentioned factors that cause swimming pool bacteria to form are often difficult to eliminate, while the risks are considerable. These pathogens can cause a wide variety of problems, such as gastrointestinal-, skin-, ear- or eye infections and breathing problems, particularly if the swimmer’s head is submerged under water.

The (dis)advantages of chlorine to eliminate swimming pool bacteria

The most commonly used method to fight harmful pathogens is chlorine, or a chemical that releases chlorine into the water. This method is fairly effective. It eliminates a large number of bacteria and some viruses. Unfortunately, a considerable number of the micro-organisms (for example Cryptosporidium parvum and Giardia lamblia) tolerate chlorine! Once swimming pool bacteria get in the pool, it can take days for chlorine to kill them – or worse: they won’t be killed at all. These are the micro-organisms that cause gastrointestinal infections (such as diarrhea) and ear infections.

The (dis)advantages of Ultra-Violet pool sanitizers to eliminate swimming pool bacteria

Ultraviolet light disinfects water by deactivating any micro-organism that may be in the water, also the ones that chlorine doesn’t affect. It takes only seconds for the UV radiation rays to deactivate micro-organisms by breaking through its cell wall and disrupting their DNA. This often totally destroys the organism, or affects its reproducing abilities.

The effectiveness of the UV pool sanitizer can be found in the wavelength frequency. When implied at the correct dose, UV is an extremely powerful disinfectant.

So, how does it work?

You might consider taking UV-C systems into your assortment. To explain the workings of UV-C we have to get a little bit technical on the topic. This helps you to fully understand the system, and therefore inform your customer as good as possible.

So, how does it work? With a wavelength range of 280 – 100 nanometer the so-called UV-C light literally nips those nasty pathogens in the bud.

The blue line on the graph shows the energy absorbance at various UV wavelengths of the DNA of a typical micro-organism. The higher the absorbance, the greater the UV penetration and the greater the disruption caused to the micro-organism’s DNA and hence the greater the inactivation rate of the microorganism.

There is significant evidence to suggest that medium pressure lamps not only generate UV wavelengths that disrupt the DNA of microorganisms as discussed above, but also generate UV wavelengths that damage the enzymes that are largely responsible for photo reactivation of some pathogens such as e-coli.

I hear you thinking: there must be any disadvantages, too. What should be taken into consideration?

  • The extent to which micro-organisms are inactivated and chloramines are destroyed depends on not only on the rate at which they are subjected to radiant energy at of a particular wavelength, but also on the duration of their exposure to that energy.

  • Can UV-C completely replace chlorine? No. It’s the insurance that the pool water that passes the UV lamp is completely disinfected. However after being released in the pool or spa, the water can be infected again. A secondary disinfectant must be added to protect the people in the water. The most commonly used secondary disinfectant is chlorine. Luckily, the chlorine concentration will always be brought down by 50-80% when using UV-C.

    Additional to being the secondary disinfectant, chlorine will also remove (oxidation) all of the remains of the killed and affected microorganisms from the water after the UV-C treatment.


To kill swimming pool bacteria that are hazardous to swimmers and bathers, chlorine is a fairly effective method to apply. But -- due to the many other negative side-effects of chlorine, and taking into consideration the swimming pool bacteria that chlorine doesn't affect, UV-C can be exactly perfect solution you and your customers are looking for.

Find out how UV-C can benefit the health of your business, download the full report on UV-C systems below.

The role of chlorine in a world of UV

Topics: UV-C systems

Posted by Arjan van der Spank on 5 February 2016
Arjan van der Spank
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