UV and ozone: Companions in managing pool water contamination

Swimmers

When it comes to contamination, bathers represent a more significant origin than the source water. Bathers, whether accidentally or intentionally, release a myriad of contaminants into the pool, including: sweat, saliva, nasal mucus, urine, fecal matter, cosmetics, body oils, suntan lotion, soap and detergent residues, skin, blood, and vomit. Some of the contamination represents a real health hazard, but in all cases, a higher demand is placed on the sanitizer, requiring more chlorine to be used (relative to a contaminant-free pool). Further, because many of the contaminant sources contain nitrogen (N) (e.g. urea in urine and sweat), chloramines are formed.
Chloramines are undesired byproducts of spent chlorine that are known to irritate skin, eyes, and the respiratory tract.

Many people would be surprised at the level of contamination caused by a single bather. Scientific studies have demonstrated that active swimmers perspire 1 L (0.26 gal) of sweat every hour, release about six million skin cells every 15 minutes, and accidentally release 50 mL (1.7 oz) of urine and 104 mg (0.14 g) of fecal matter per bathing event (see Table 1). Naturally, some of the released contamination is accidental; however, it is well-known many swimmers (17 per cent in one report) intentionally urinate in the pool. Fortunately, urine is sterile and poses no microbial health issue (provided the bather does not have a urinary tract infection); however, urine contains a significant quantity of nitrogen compounds (i.e. urea) which leads to the formation of chloramines.

The habitat

The environment represents the third source of pool water contamination. In outdoor pools exposed to the elements, water can become contaminated from windblown debris, rain containing microscopic algae spores, insects, bird and rodent droppings, pets (e.g. dogs), and water from unsanitary sources (e.g. rain runoff). Indoor pools, including those protected by a screen enclosure, are less susceptible to environmental contaminants.

Impact of contamination

Perhaps the most serious issue with pool water contamination is the potential for illness due to microbial introduction. Swallowing just a little water that contains these germs can make a bather ill. In fact, studies have shown the average swimmer ingests 50 mL (1.7 oz) of water for every hour of swimming.

Pathogenic microbes, which include bacteria, viruses, protozoans, and fungi, are of greatest concern in pools as they have been associated with numerous recreational water illnesses (RWIs).

In the U.S., the Centers for Disease Control and Prevention (CDC) regularly monitors pool-related health outbreaks and have identified Cryptosporidium as one of the leading causal agents with nearly 10,000 reported cases in 2008 alone. Diarrhea is the most common reported illness associated with pathogenic contaminants, but otitis externa (i.e. swimmer’s ear), as well as skin rashes and respiratory infections, also occur frequently.

Unfortunately, young children, elderly persons, and individuals that are immunocompromised can become very sick (and even die) when infected with waterborne microbes. Contrary to popular belief, chlorine does not kill all microbes instantly. Some microbes, such as Cryptosporidium, are very tolerant to chlorine, requiring several minutes to several hours of chlorine exposure before microbial populations are reduced to safe levels.

The World Health Organization (WHO) has categorized various types of micro-organism hazards that can exist in recreational water as fecally derived or non-fecally derived (see Figure 2). Recognizing the variety of micro-organisms that can exist in pool water, a prudent strategy is always to employ multiple disinfectant types, where practical, to ensure sanitization success.