Is chlorine enough to blitz the bugs?

Usually, a swim in the local pool will result in wet hair, tired muscles and skin smelling of chlorine. Some people like the scent, others give the soap a good work-out trying to get rid of it. But why do we need chlorine in pools anyway?

The chlorine is there to help keep the water free of bacteria and other microorganisms. To do this, pools require a constant level of chlorine in the water at all times. When chlorine is added to the water, it breaks down into different chemicals, including hypochlorous acid (HOCl) and hypochlorite ion(OCl⁻).

These work to kill microorganisms and other nasties by breaking through their cell walls and destroying their inner proteins, enzymes and processes, effectively deactivating them.

While many people think that chlorine kills germs instantly, this isn't the case. It actually takes different times for the same amount of chlorine to work, depending on the microorganism. Chlorine will kill bacteria such as E. coli in less than a minute, but takes around 16 minutes to kill the hepatitis A virus. It needs 45 minutes to kill Giardia, and up to 10 days to kill Cryptosporidium.

For chlorine to be most effective against pathogens, the pH level of the water should sit between 7.2 and 7.8 on the acidic-basic scale (where 0 is most acidic and 14 is most basic). It's also recommended that the concentration of chlorine sits around 1 to 3 parts per million (ppm). Less than 1 ppm allows bacteria and algae to begin to thrive.

Outbreaks of water-borne disease in recreational swimming pools due to faecally-derived viruses and bacteria have generally been associated with inadequately chlorinated or non-chlorinated water. Thankfully, these outbreaks are quite rare as public pools are held to strict water monitoring and safety standards.

In addition to chemical means, such as adding chlorine or bromine-based disinfectants, pathogenic microorganisms can also be inactivated by physical methods, such as treatment with UV radiation. Filtration of pool water also plays an important role in removing microorganisms and in maintaining free chlorine levels.

Swimming is a great activity on a hot day. You can do your bit to help chlorine do its job by taking a few common sense measures like:

• staying out of the water if you’ve recently had diarrhoea
• taking small children for frequent loo breaks
• having a shower before swimming, and practising good hand hygiene at all times
• using swim nappies for babies, and changing them often (in the change room, not poolside).

Follow these simple rules and everyone should be a happy swimmer!