UV and ozone: Companions in managing pool water contamination

By Ray Denkewicz

Properly maintained pools can be a great source of fun and relaxation for the nearly 500,000 inground pool owners across Canada. As open bodies of water, however, pools are subject to contamination, not only from active bathers, but also from the natural environment in which they reside.

While chlorination tends to be the primary method in which homeowners manage swimming pool water contamination, other advanced water treatment methods exist which are also quite effective. For instance, ultraviolet (UV) light and ozone are two such technologies which are excellent supplementary water treatment methods for pools. This article discusses how UV and ozone can be employed to complement chlorine in the battle against the inevitable—pool water contamination.

Sources of contamination

Broadly speaking, there are three distinct sources for contaminants entering any pool: the source water, bathers, and the environment (see Figure 1).

Where did the water come from?

In most cases, source water for pools comes from the drinking water supply and, as such, is safe and low in contaminant levels. However, municipal supply of drinking water can have significant concentrations of chloramines—as much as 3 mg/L (3 parts per million [ppm])—due to the fact many drinking water management plants use monochloramine as part of the water treatment regimen.

Monochloramines are used because they are chemically more stable throughout the water distribution system, helping to keep the supplied drinking water free of bacteria and biofilm. Further, they are less objectionable than other forms of chlorine in terms of taste and odour.

For roughly 25 per cent of Canadians, groundwater or well water is the major source. Generally, this water is clean and free of disease-causing micro-organisms because the soil acts as a filter. Since this is not always the case (e.g. a leaking septic system, livestock waste), well water should be tested regularly.

In addition to the potential for micro-organism contamination, groundwater can vary considerably in the levels of inorganic compounds such as calcium (Ca), iron (Fe), manganese (Mn), hydrogen sulfide (H₂S), and organic contaminants such as tannins (from decayed wood and leaves). These types of contaminants pose no serious health consequences, but can be annoying in pools as they can create water imbalance (calcium), stains (iron and manganese), water discolouration (iron, manganese, and tannins) and odours (hydrogen sulfide).