Swimming Pool Blog

Disinfection Byproducts in Pools

disinfectant byproducts blog post
by Rob Cox February 28, 2015

An article by the Cleveland Clinic caught my eye recently. It's not a new story, for forty years there have been some known link between swimming in indoor chlorinated pools and health risks caused by inhaling or absorbing chloramines, and more specifically, trihalomethane (THM's), Haloacetic Acid (HAA's) and other disinfectant byproducts.

There are over 600 known disinfection byproducts (DBP's), and most are also volatile organic compounds (VOC's). DBP's are the result of reactions between organic and inorganic matter in water with chlorine used to disinfect, or sanitize an indoor pool.

The DBP's that are most studied are THM's. Among THM's, there are four distinct but related compounds: chloroform (CHCl3), bromodichloromethane (CHCl2Br), dibromo-chloromethane (CHClBr2), and bromoform (CHBr3). Of the four, chloroform is the most prevalent trihalomethane in pools - but there are many others.

Chloramines for instance, are also DBP's. As you may already know, chloramines (aka combined chlorine) are created when a free chlorine molecule bonds with an ammonia or nitrogen molecule. The resultant molecule emits a strong smell of chlorine and is irritating to skin and eyes, and is no longer an active sanitizer. Chloramines can move from mono and di-chloramines, into a trichloramine, which has the most potential as an irritant to lungs, skin and eyes.

DBP's in pool water have been linked to respiratory problems, most notably in young children, ages 1-4. There have also been studies that have found some correlation between drinking water THM's and cancer of the bladder or colon. However, this risk is very small, and the World Health Organization (WHO), has stated that the "risk of illness from pathogens is at least 10 000 to 1 million times greater than the risk of cancer from DBPs"

10 ways to Deal with Disinfection Byproducts in Pools

1. Don't overchlorinate. Free chlorine that is idle will find some trouble to get into - if there is more chlorine in the pool than is needed, unused chlorine will eventually form into byproducts.

2. Switch to Bromine. Although bromine also has it's share of disinfection byproducts, namely bromoform, the effects and amounts of THM's encountered with bromine are less than with chlorine.

3. Use Ozone. To reduce your reliance on chlorine, and reduce the amount of chlorine used, you could supplement chlorine with ozone treatment. However, ozone also creates disinfectant byproducts.

4. Use Ultraviolet Radiation. UV systems use UV-C rays to zap contaminants, and since it's just light particles, there are no combinations made and no DBP's.

5. Use Minerals. For the same reason as using ozone or UV light, the use of a mineral purifier as a supplemental sanitizer will reduce the need for so much chlorine in the pool.

6. Change the Water. For indoor pools, or outdoor pools in areas of low rainfall, the water can become choked with byproducts of disinfectants over time. This may create a bio-hazard in pools that are used heavily, in addition to elevated levels of dissolved solids. If possible, pool water should be changed every 2-3 years for indoor pools and every 3-5 years for outdoor pools - given budget or drought concerns in many parts of the country. Recycling pool water is also available in some areas.

7. Shock as Needed. Removing combined chlorine regularly helps prevent elevated levels of THM's. Use a DPD test kit and shock whenever the Combined Chlorine test (reagent #3) is more than 0.3 ppm.

8. Keep pH Low. When your pool pH is higher than 7.4, it makes it easier for combinations to occur, because it makes free chlorine slow and sluggish. Help out your HOCL, and maintain your pH level in the 7.2-7.4 range, with Alkalinity of 90-110.

9. Shower before using the Pool. In heavily used pools, this alone can dramatically reduce the formation of disinfectant byproducts created by combinations with body wastes and chemicals that are brought into the pool by users.

10. Overfilter the pool water. I have always been a proponent of the BIG pool filter, and of running the pump a few hours longer than needed, for the benefit of better water clarity with fewer contaminants. When you filter the pool more (or better), you can enjoy better water with fewer chemicals!


PS - The issue of disinfectant byproducts is mainly a concern for indoor pools with high bather loads - no worries if you have an outdoor residential pool! 


- Rob