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Wading Pool Research

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Toronto Public Health says no one can be in a wading pool when it’s draining, because the suction of the water going down the drain could injure or even kill a person.

In Canada’s main hospital database, out of almost 1.5 million records over 13 years, only 2 cases of body-part entrapment at wading pools were recorded (and “entrapment” could mean getting a foot stuck in a broken wading pool grate – not necessarily having anything to do with water and suction).

A Sept. 2005 search of the CHIRPP database (all ages, 1,479,302 records total, spanning 1990- 2003) for cases of body part entrapment in pools, wading pools and hot tubs/Jaccuzzi’s/whirlpools was conducted.....Of the 35 cases, 29 happened in a pool (in- or above- ground), 4 in a hot tub and 2 in wading pools. (Source: Public Health Agency of Canada, pool entrapment.)

The idea that a draining wading pool can have lethal suction comes from an occurrence in a Minnesota “kiddie pool” that was missing the cover over its water recirculation drain. Water is re-circulated by a powerful suction pump. A little girl got stuck sitting on top of the uncovered drain opening, and the force of the pump formed a vacuum. She was badly injured internally, and later died.

Public Health sent us this link about the little girl, to show why all children are now removed from Toronto wading pools before they start draining.

But Public Health is comparing apples and oranges. The Minnesota “kiddie pool” was built like a real swimming pool, with a suction pump to circulate the water. Toronto wading pools have no suction pump – they are filled and drained like a bathtub. If you stand on top of the anti-siphon drain covers of any of our “fill-and-drain” wading pools, while they’re draining, they tickle your toes. That’s all.


Toronto Public Health instructed Parks staff to increase the amount of chlorine in wading pool water. They said this was necessary because children could get very sick with infections if there was less chlorine.


All pools contain e-coli, so do puddles, gutters, gardens and human intestines. Most e-coli are benign or even helpful. But there are several kinds that, though very rare, can make young children and old people very ill with diarrhea.

E. coli O157:H7 In 1998, 26 children in a wading pool in a large Georgia (U.S.) water park got sick with this rare and nasty form of E-coli. Seven of the children were hospitalized and a 2-year-old girl died from Hemolytic Uremic Syndrome, a kidney disorder she got from E. coli O157:H7 The water park was sued for millions of dollars -- a story that must have rattled swimming pool operators all over the world.

It appears that the chlorine levels in this pool were very low. But that was not the only problem. It was a “kiddie pool,” which worked like a swimming pool, not a “fill-and-drain” wading pool. The pool was not drained at night, even though there may have been several diaper accidents by small children. The water was merely re-circulated, and so new outbreaks continued over four days before they were noticed. The cause of the outbreak was never determined for sure, but investigators assumed that persistence of bacteria in pool water overnight was the likely reason why children sickened over four days.

In a “fill-and-drain” wading pool the water is completely drained away every evening. Every morning the wading pool surface is swept and pressure-hosed. So the persistence of bacteria overnight is much less likely than in regular swimming pools – including shallow “kiddie pools” – that keep their water in.


Cryptosporidium is a parasite that is resistant to chlorine. It causes watery diarrhea but it typically does not cause serious illness in healthy people. Small children and people with low immunity are more vulnerable. The parasite is introduced by mouth, often in swimming pools.

The good news is that cryptosporidium is damaged by ultra-violet light -- sunlight. Indoor pools have to get a UV machine, but outdoor wading pools have easy access to direct sun. And in the case of "fill-and-drain" wading pools, the sun can continue to reduce residual parasites on the concrete after the water is drained every day.


Regulations for Ontario wading pools: "there [must be] a chlorine level of equal to or greater than 5 mg./L in wading pools."

Regulations for Ontario swimming pools (indoor and outdoor): "there [must be] a residual of free available chlorine in every part of the pool of not less than 0.5 milligram per litre."

Regulations for Ontario spas: "there [must be] a residual of free available chlorine or total bromine of at least five but not more than 10 milligrams per litre."

Chlorine level recommended for swimming pools by the U.S. Centre for Disease Control: 1.0 - 3.0 ppm (or 1 to 3 mg/L).

"The disinfection of chlorine is based on the penetration of the negatively charged chlorine-products through the negatively charged cell wall of microorganisms. Inside the cell, the chlorine interacts with enzymes leading to inactivation or cell death. Besides this positive reaction of chlorine, side reactions occur. Disinfection By-Products (DBPs) are formed, which are irritating and can be harmful to swimmers health. One way to lower the formation of DBPs is by lowering the chlorine concentration to a minimum level, where disinfection is still sufficient....." Source: MINIMUM CHLORINE CONCENTRATION IN SWIMMING POOLS TO ENSURE DISINFECTION, Peters M.C.F.M.(a,b) et al, Delft University of Technology, Department of water management, and (b) Delft University of Technology, Department of environmental biotechnology, The Netherlands; p.66.

"Chlorine concentrations in pool water may vary widely in different countries (MMWR Morb Mortal Wkly Rep 2003 52, 513-516) and are mainly a result of traditions and not of scientific considerations. Up to now, there is no reliable scientific evidence on chlorine concentrations necessary in swimming pools to avoid the outbreak of diseases. Whilst in Germany concentrations between 0.3 and 0.6 mg/l are applied, WHO recommends 1.0 mg/l free chlorine in the pool water, and in many countries chlorine dosage is even significantly higher." Source:Erdinger L. University of Heidelberg, Department for Infectious Diseases, Microbiology and Hygiene, Environmental Laboratory, Heidelberg, Germany.

From the National Collaborative Centre for Environmental Health (NCCEH, funded by the Public Health Agency of Canada "to foster linkages within the public health community.") Pool chlorination and closure guidelines, March 2011: "....in email correspondence with the US CDC [Centre for Disease Control] concerning maximum FAC [free available chlorine] levels, it was mentioned that although it is common practice to close at 10 ppm, the correspondent was not aware of any “definitive information” to support this level.....while there is no specific evidence to support the 10 ppm level used as an upper limit for pool closures based on health effects through ingestion, inhalation, and dermal exposure, animal studies on eye irritation do provide some evidence for the 10 ppm FAC limit."

The U.S. Centre for Disease Control corroborates the uncertain academic evidence for how much to chlorinate: "Understanding the types of contaminants and the magnitude of disinfectant demand by various environmental factors (e.g., particulate) is an essential component to design and operate a recirculation and filtration system. Limited data currently exists..." (July 2012)

Minneapolis/St.Paul (Ramsey County): A public pool must be closed immediately if the total disinfectant residual is above 10 PPM. Source: Pool Chemistry Requirements.

A mother of two young children submitted a Freedom of Information request in May 2014 to find out the actual incidence of infection or injury in Toronto wading pools. She asked about the last twenty years, and got this answer: Communicable Disease Control staff say that “no outbreaks have been associated with recreational water facilities” during that time period. And the city’s Healthy Environments data collection staff said that “they do not track the information being requested because it is not part of their routine data intake.”


"Most DBPs identified so far are chlorinated compounds, trihalomethanes (THM) and chlorinated amines being the most important. Therefore, regular analysis of main DBPs should be included in every monitoring program.” Source: A REVIEW ON MONITORING AND DISINFECTION ISSUES Erdinger L. University of Heidelberg, Department for Infectious Diseases, Microbiology and Hygiene, Environmental Laboratory, Heidelberg, Germany, p.20.

There is no reference in Ontario regulations to monitoring DBPs -- they're not mentioned.

"Recently, another volatile DBP (trichloramine) being formed as a part of Combined Chlorine (CC) was blamed for lung hyperpermeability and an increase in asthma prevalence in schoolchildren" source 1 and souce 2 "Trihalomethanes are suspected to have negative effects on birth such as, low birth weight, intrauterine growth retardation in term births, as well as gestational age and preterm delivery. There are also some evidences showing these by-products to be mutagenic and carcinogenic, the greatest amount of evidence being related to the bladder cancer." Source: Mohammad Reza Mohammad Shafiee and Lobat Taghavi. "Health Effects of Trihalomethanes as Chlorinated Disinfection by Products: A Review Article" World Academy of Science, Engineering and Technology 68 (2012): 2090-2096.

Austria: "The new regulation has now included the parameter Trihalomethans (THM) on the one hand as harmful substances themselves and on the other hand as indicator for total DBP levels. The concentration of THM in pool water should be less than 20 μg/L and must not exceed 100 μg/L." Source: A NEW LEGAL REGULATION FOR THE QUALITY OF BATHING WATER IN AUSTRIA, Sommer R., Holzhammer E. Medical University Vienna, Institute for Hygiene and Applied Immunology, Water Hygiene, Vienna, Austria.


Intermittent draining: National Post article, July 11 2011, CTV News Item, July 11, 2011, Toronto Star, July 10, 2011

Correspondence with the Ministry of Health about de-facto wading pool regulation despite current legislation

Content last modified on August 01, 2014, at 10:28 PM EST