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Mitigating health risks in active pools.

A new wave of leisure pools is appearing in public parks and recreation areas. These leisure pools range from wave pools through lagoons, water flumes, and lazy rivers to interactive pools. The wading pools and spray pools seen in many parks had one or two low-velocity spray heads and usually drained directly into municipal sewer systems. Few such pools contained water more than 6 in. deep.

Today's interactive pools range up to 18 or more in. deep and use between 1,500 and 2,000 gallons of water per minute. As a result, the basic principles of disinfection, filtration, and circulation over the decades as applied to swimming pools take on new meanings.

Disinfection keeps the numbers of normally harmless microorganisms that will always be present to a minimum and helps ensure that any harmful organisms that might enter the pool are rapidly inactivated to prevent transmission to bathers. Such disinfection includes both the water body and the filter beds. Contaminants include sweat, skin particles, mucus, blood, urine, and feces. Chlorine is the chemical most commonly used to destroy potentially harmful microorganisms. In reacting with the organisms, the chlorine or other chemical is itself destroyed, whose loss must be offset to ensure that there is a residual level of disinfectant chemicals in the pool to deal with newly added pollutants.

The pH that is derived from hydrogen-ion concentration is critically important in pool water chemistry. The higher the hydrogen-ion concentration the lower the pH value. Continuous monitoring of the pH value is necessary to keep it between 7.0 and 8.0. The amount of chlorine or other disinfectants required is proportionate to the volume of water and the bathing load in the leisure pool.

Filtration keeps the water clear and clean. Reduced clarity can compromise disinfection. Turbidity - which should be kept to 0.6 ntu or less - is caused by suspended colloidal or particulate matter. Proper filtration coupled with coagulation converts the colloids into a filterable flocculus. Sufficient filtration capacity must exist to cope with the designed circulation rate and turnover period. Since the bathing load for such pools of shallow water is one bather per sq meter, the circulation rate can be established.


Circulation is the repeated movement of the entire volume of water to and from the pipes and treatment system. The circulation rate equals the bathing load times 1.7, which then determines the turnover period. The turnover period equals the water volume divided by the circulation rate. Leisure pools 0 to 5 m deep should have a rapid turnover rate because they are subject to heavy bathing loads, which can increase pollutant concentrations. The addition of play features further enhances the bather load.

Circulation is the culprit that must be addressed in the interactive pools. A recent case involving an interactive leisure pool in a warm weather state generated much attention after a young bather discharged feces (diarrhea as opposed to solid stool) into the water. The rapidly dispersed fecal coliforms or E. Coli could not be consumed quickly enough by the chlorine present. At least eight children suffered gastrointestinal infection, several seriously, after ingesting remaining bacteria or exposure possibly through skin, skin glands, and mucous membrane contact.

Besides gastrointestinal effects some of the children suffered hemolytic uterine syndrome, which can cause kidney failure. Such microorganisms as cryptosporidium and giardia and E. Coli from fecal matter can become deadly when the sun coupled with high ambient temperatures warm the water in shallow volume leisure pools. Most microorganisms living in water grow best at a temperature of around 22 [degrees] C, while those associated with the human body - including human pathogens - grow best at a body temperature of 37 [degrees] C. Therefore, as typical pool water warms up in shallow pools, so does the probability increase for disease.

A case example of an interactive pool in New York state reflects a design intended to mitigate potential problems as previously described (See Table 1).

This example incorporates an ultraviolet radiation system installed in the full re-circulation pipework of the pool so that the water is treated continuously. A disinfectant, usually chlorine based, is used alongside UV to maintain a disinfectant residual (say, 0.5 to 1.0 mg/v) in the pool. UV inactivates bacteria and helps break down chloramines and other pollutants but also breaks down chlorine.

Pool Type:

Toddler Pool 1 to 2 yrs sq ft
Pre School/Primary Pool 2 to 8 yrs sq ft

Pool Depth: Toddler Pool
Pre School/Primary Pool

Pool Water Volume: Toddler 5,640 gal
Pre School/Primary 15,625 gal

Pool Water Pump FLow:

Toddler                   Flow       Flow total      Est

(4 lesson days)            35            140
Pre School/Primary
1 tumble bucket           100            100
1 rain drop               400            100
1 pop jet                 150            150
1 tee cup                 425            425
1 sheet flow              400            400

Total                                1,625 gpm

Pool Capacity (load)

Pre School/Primary

Pool Turnover Rate: 1 hour turnover
Toddler Pool Pump 5, 640 gal x 1 hr = 94 gpm
Pre School Pool Pump 15 625 gal x 1 hr = 260 gpm

Disinfection/Filtration/Circulation System

Toddler Pool: Apparatus spray water flows from Pre School/Primary
treatment plant through spray into Toddler Pool; to main drain, to
pump; to sand filter; to chlorinator; to UV device; return to pipe
and pool bottom inlets to apparatus sprays.

Pre School/Primary: Apparatus sprays water flows from
Pre School/Primary treatment plant through spray into Toddler Pool;
to main drain; to pump; to sand filter; to chlorinator; to UV device
to pipe and pool bottom inlets to apparatus.

In addition to the hydraulics of the treatment plant and its location, size, access spaces, and environment which encompasses the disinfection, circulation, and filtration systems, the administration of the pool is important. The administration includes admission, regulation, reaction, and education elements.

Admission is controlled through signage, surveillance, and enforcement of the requirements. Signage should limit:

* The age group in each pool (limit ___)

* The bather load in each pool (limit ___)

* The companion - parent or other responsible adult in attendance

* The bathing attire - for toddler, a waterproof disposable diaper or other waterproof pants

* The hygiene of the bather - no open wounds, infections, toileting, powders, creams, lotions, or oils.

An attendant should check all entrants for adherence to the requirements and make sure no improper bathing attire is worn. Rules and regulations must be enforced, with prohibition or restriction of use for those bathers failing to comply.

Regulation is determined through policies established by the village trustees and posted. It also prohibits crowding, and specifies cleaning and hygienic procedures.

Reaction is the response to emergency situations (e.g, loose, funny stool from diarrhea or pants breaking introduced into the water). This includes:

* Clearing the pool of bathers immediately

* Maintaining disinfectant levels at the top of the range

* Emptying the pools when fecal discharge is suspected

* Cleaning, vacuuming, and disinfecting the pool before reopening

* Adding a coagulant and filtering for three turnover cycles

* Backwashing as recommended for the filter

Other pollutants are retrieved and allowed to disperse and be neutralized by the disinfectant in the water.

Education encompasses pre-bathing hygiene such as proper toileting procedures, good housekeeping, knowledge of the potential problems, and proper disposal of diapers after bathing.

These efforts will mitigate the contamination of the interactive play pool and infection of bathers.

Dr. Mittelstaedt is Executive Director, Recreation Safety Institute, Ronkonkoma, New York.
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Author:Mittelstaedt, Arthur H., Jr.
Publication:Public Works
Date:Jun 1, 1999
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