June 2017 - Parks & Recreation - 49

the deepest part of the pool) and during
times when swimmers are not present
(e.g., overnight or during periods of
closure). The reason for this is because
bacteria, such as Pseudomonas and Legionella, can grow and reproduce in unsanitized water. These organisms can form a
slimy layer, called biofilm, which is very
hard for sanitizers to get into to kill the
organisms harboring there. So, even if
a sanitizer residual is reestablished, it
may not be able to penetrate the biofilm.
There are numerous products that
claim to kill bacteria, but unless the
product is a sanitizer registered by
the Environmental Protection Agency (EPA), as indicated on the label, it
is not a sanitizer. The EPA regulates
chemicals used to kill pathogens in
pools. The only chemicals and systems
that are EPA-registered for use in sanitizing pools are chlorine, bromine,
PHMB (polyhexamethylene biguanide) and some metal systems. There
are some treatments, such as UV and
ozone, which are very good at inactivating hard-to-kill pathogens, like
Cryptosporidium (crypto). However, UV
and ozone cannot be used as primary
sanitizers in pools because a residual
cannot be maintained in the pool to
prevent bather-to-bather disease transmission. UV and ozone are often used
as secondary disinfectants in high-risk
facilities, but a primary sanitizer residual must always be present. Chlorine
is the most common sanitizer used in
pools, and its concentration should be
maintained between 1 and 4 parts per
million (ppm).
We know that pathogens are constantly being introduced into the pool, but
there are also certain events where gross
contamination occurs: vomit, formed
stool and diarrheal accidents. The CDC
has studied the pathogens that may be
present in these events and has provided
guidelines for treatment on its Healthy

Table 1: Disease-Causing Organisms and Outbreak Statistics
Group

Species

Typical Health Effect Outbreaks* Cases*

Hospital*

Bacteria

Pseudomonas
aeruginosa

Rash

2 (4)

16 (56)

0 (0)

E. coli

Diarrhea

Shigella sonnei

Diarrhea

Legionella spp.

Respiratory illness

9 (2)

33 (52)

18 (1)

Cryptosporidium spp. Diarrhea

874

Giardia

Diarrhea

Norovirus

Diarrhea

2 (2)

122
(21)

0 (4)

Parasites
Viruses

* Values in parentheses are not confirmed to be the specific pathogen.

Hyperchlorination Tables
No Stabilizer Present

With Cyanuric Acid Stabilizer Present

Free Chlorine, PPM

Time, Hours

Free Chlorine, PPM

Time, Hours

12.75

25.5

8.5

Swimming website and in its Model
Aquatic Health Code. The steps in these
remediation procedures should be carefully followed to prevent an outbreak.
For example, below are the basic steps
for treatment of diarrhea in the water:
Step 1: Close the pool to swimmers
Step 2: Remove as much fecal material
as possible (vacuuming is NOT recommended)
Step 3: Using unstabilized chlorine,
hyperchlorinate the pool (see tables
above for dosages and times) with the
filtration system operating and maintaining the pH below 7.5
Step 4: Backwash the filter
Step 5: Reduce chlorine concentration
to 1 to 4 ppm.
Step 6: Allow swimmers back into the
water
If stabilizer is greater than 15 ppm,
partially drain pool to reduce stabilizer
to less than or equal to 15 ppm.
The reason there are different hyperchlorination instructions with the stabilizer is because the stabilizer slows the

disinfection rate of the chlorine. The
CDC performed a study with crypto and
found that with greater than 15 ppm of
cyanuric acid, it was not able to obtain
the required reductions. The values in
the stabilizer table were obtained from
its study.
It is essential that all members of the
pool staff are trained in RWI prevention and their local health code(s). They
should also be familiar with how and
why (i) patrons can contribute contamination, (ii) an EPA-registered sanitizer
residual is maintained in all parts of the
pool at all times and (iii) contamination
response protocols are followed. The
pool operators, lifeguards and swimmers
all play a part in preventing disease transmission and ensuring that a safe, healthy
pool can be enjoyed by everyone.
Detailed references for this article are available at www.parksandrecreation.org/2017/
June/Recreational-Water-Disinfection.
Ellen Meyer is the Product Safety and
Government Affairs Manager at Lonza (ellen.
meyer@lonza.com).

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