Disinfection &
Reducing its Cost
Using Ultraviolet Light

I. Chemicals MUST be used for Pool Water disinfection:

Many people hear the word 'chlorine' and are immediately reminded of their local pool where the smell can be unpleasantly obtrusive.

Chlorine has a bad reputation because of this but society as a whole relies on Chlorine as the most important chemical that is used in the disinfection of most food products including the water in your tap.

Recreational pools are vitally important facilities, but many are understaffed and overcrowded and the quality of the water suffers.

II. Why do we need to disinfect the water in our swimming pools?

Why do we need to add chlorine to pool water if the pool water is fed by the mains and is safe to drink?

The water may be healthy when it enters the pool but bathers soon change that!

Despite all the encouragement provided to shower before pool entry most people do not and shed makeup, ointments, creams, sweat and catarrh into the pool water as well as any viruses they are carrying. One person can lose up to 700 mL of sweat during one swimming session.

Some people are or believe they are allergic to chlorine and want a swimming pool that does not rely on it to disinfect the water. Unfortunately this is not possible at the present time because there is no other form of water treatment that is guaranteed to be safe. Probably every healthy pool in the world uses either Chlorine, Bromine or Peroxide and it is important to understand why that is the case.

III. Diseases that can occur:

Swimming pool water contains bacteria that can cause many types of diseases in humans. The bacteria that cause these diseases are known as pathogenic bacteria and the pool water disinfection process must kill these for the pool to be safe to swim in.

The disinfection of Water in the past has always relied on Chlorine because it is a very efficient sanitizer and has always been relatively cheap. However it is getting more expensive and there are a few doubts about its absolute safety when people are exposed to it over a long term. Because of this a great deal of research has been carried out to find other methods of cheap, reliable water treatment that will kill the pathogens.

IV. What are the Alternative Disinfectants to Chlorine or Bromine?

The water disinfection properties of ultraviolet light were discovered over 100 years ago. The light must be at a specific wavelength and power to treat the water as it passes through a treatment cell. The UV light causes biological changes that kill the pathogens and significantly reduce the concentration of bacteria in the water, without leaving any dangerous by-products.

However the water must be totally transparent without any turbidity for the UV light to be totally effective (Turbidity is a measure of how transparent water is and increases due to the presence of particles in the water).

It is also very difficult to measure how effective the UV light treatment is. With Chlorine this is easy because the water is treated with sufficient chemical to make sure that there is enough residual chlorine to ensure that the pool water is safe.

So the UV treatment needs a filter to ensure that the water is never cloudy, but this filter will also harbour a seething mass of bacteria (See other article on Swimming Pool Water Quality).
The result of all this is that UV can be used to reduce the amount of chemicals used but every pool will still need a residual level of chlorine in the water for it to be 100% safe.