Assessment of the Microbiological and Physico-Chemical Quality of the Swimming Pool Waters in Zanzibar Hotels: A Case Study of North Region-Unguja, Zanzibar, Tanzania

Swimming pools’ water has been a significant source of microbial infections. Most of swimming pool users are unaware of the dangers of the infections that may be brought by bacteria within the swimming pools. This study aimed to assess the microbiological and physicochemical quality of swimming pool waters in Zanzibar hotels in North A and B Districts of Unguja, Tanzania. A cross-sectional study design was used. Sixteen swimming pool water samples were collected for both microbiological and physicochemical analysis using standard laboratory techniques. Data about awareness and training of swimming pool managers was also collected using interviews. The data was analyzed using SPSS (Version 21). A one-way analysis of variance (ANOVA) was used to determine significant differences (p ≤ 0.05). The study found that 68.5% of pool water’s pH readings were outside the WHO’s recommended range. Also, the study found that 31.25% of pool water’s residual chlorine level readings were outside the WHO’s recommended range. Temperature and turbidity met the WHO acceptable standards. The study also revealed that 50% and 87.5% of the water samples had Total Colony Counts(TCC) levels above the WHO-recommended level of heterotrophic bacterial count (≤200 CFU/mL) before and after the pools were filled, respectively. Furthermore, 75% of water samples had total coliform counts above the recommended limit (MPN≤ 2/100 ml). After the pools were filled and used, there was a slight decrease to 56.3%. E. coli was detected in 12.5 % of water samples, while no Salmonella or Shigella were detected. The study elucidated that some swimming pool waters required proper management. Also, there is a need to strengthen and enforce water quality regulations to ensure the safety and health of swimmers in the swimming pools. 

Introduction

Swimming pools are preferred by most bathers over rivers and streams (Kuzgunkaya & Yildirim, 2010). The swimming pool’s operational rules and principles state that everyone who enters the water must have a soapy shower, and anyone with a skin disease is not permitted to use the facility (Wiltse, 2007). Bathers may contribute to pollution on their own, according to some theories, either by shedding bodily bacteria or by stirring up contaminated sand and silt. According to studies, harmful bacteria can enter swimming pools either directly or indirectly through the soil, sewage, contaminated air, or dust (Abbottet al., 2011). Additionally, people who use pools when sick may contaminate the water with bacteria through their skin, mouth, urine, unintentional faces, contaminated objects and clothing, airborne pollution, incoming water from an unclean source, and bird droppings (Okwelle & Nwaokugha-Douglas, 2020). Cholera, trachoma, gastro-enteritis, upper respiratory infections, skin sores, and diarrhoea can be brought on by swimming in contaminated pool water (Lederet al., 2002). The sewage industry, surface runoff, domestic animals, and wildlife are additional sources of fecal pollution (Mülleret al., 2020). Studies have shown that various microorganisms, including norovirus, can cause illness outbreaks in recreational water, with norovirus being responsible for the largest outbreak. These microorganisms include Campylobacter jejuni, E.coli O157:H7, Shigella sonnei, Cryptosporidium spp., Giardia intestinalis, and norovirus (Mattioliet al., 2021). Epidemiological studies found a link between gastrointestinal illnesses and water quality when the pollution sources were discharging water to the swimming environment (Dressinget al., 2016). Maintaining public health can be significantly harmed by inadequate pool disinfection and poor cleanliness (Oluyegeet al., 2020). Due to their lack of rotavirus immunity, young children, the elderly, and those with compromised immune systems are at higher risk (unless they have received an immunization). These individuals are more vulnerable to illness from recreational water (Fewtrell & Kay, 2015). One of the world’s most well-known tourist sites, Zanzibar Island, gets a sizable number of visitors each year who contribute to the expansion of the local economy. There are numerous hotels with star ratings ranging from zero to five, even though the bulk of hotels with swimming pools are in the two- to five-star hotel category. Despite the fact that various global research relating to swimming pool quality, safety, and hygiene have been conducted and findings were published for proper management, in Zanzibar, there are no scholarly studies on this area. Thus, the safety and quality of the Zanzibar hotels’ swimming pool waters are largely unknown. Hence, the relevance and importance of carrying out this investigation to highlight on the current condition and determine whether the swimming pool water complies with established national and international requirements are hereby justified. The findings of this study are expected to raise awareness of respective agencies and policymakers to formulate appropriate decisions regarding effective management of swimming pools in Zanzibar so as to safeguard the public health of the Zanzibar community and visitors.

Methodology

The study was carried out in the north region of Unguja in Zanzibar Island, Tanzania Fig. 1. Geographically, the Zanzibar Islands are in the Indian Ocean. This study was carried out specifically in the North Region of Unguja. The region has a temperature range between 20°C and 40°C with a tropical climate. The region also experiences a bimodal pattern of precipitation, with a lengthy rainy season (called locally in Kiswahili as “Masika”) and a brief wet season (known as “Vuli”). The longer rainy season occurs every year from March or April to May, whereas the shorter one occurs from September or October to December. During the long-wet season, the region receives annual rainfall between 900 mm and 1200 mm, and between 400 mm and 500 mm during the short rainy season.

Fig. 1. Map of Unguja showing north district A and B. Source:  https://commons.wikimedia.org/wiki/File:Zanzibar-north-district.

Study Design

The study used a cross-sectional design to evaluate the microbiological and physicochemical quality of swimming pool water in Zanzibar hotels.

Sampling Technique

A purposive sampling method was used to choose the hotels that have swimming pools. A survey of hotels was conducted based on accessibility and agreement from the hotel administration (Nyimbili & Nyimbili, 2024).

Sample Size

Sixteen water samples from swimming pools were taken in an aseptic setting in sterile polythene bags that were sent right away to the Zanzibar Food and Drug Agency (ZFDA) for physicochemical and microbiological analysis. Furthermore, 16 swimming pool owners and operators were interviewed for their awareness of hygiene practices and whether they attended training about swimming pool management.

Physicochemical Quality Analysis

Temperature

The temperatures of the water samples were determined using a thermometer and recorded using the centigrade (°C) unit.

pH

The electrode of pH meter was inserted into each beaker containing the. The sample was then stirred moderately and uniformly using a stirring rod. Then the pH was recorded as displayed after waiting at least 1 min to 2 min for a stable reading.

Turbidity

The samples were thoroughly stirred to mix and disperse the solid particles present in the water samples. After the bubbles disappeared, the samples were then poured into the turbidimeter tube. The turbidity was then read directly from the instrument scale display and recorded. Turbidity was measured in nephelometric turbidity units (NTU).

Residual Chlorine

The residual chlorine was measured using the dpd (diethyl paraphenyline diamine) indicator test using a comparator, where one tablet was added in a test chamber. The tablet was crushed, then the chamber was filled with the water supply under test. Then the same water supply under test (without a tablet) was placed in the second chamber for a blank control for color comparison. The level of residual chlorine in milligrams per liter (mg/l) of water was determined by comparing the colour of the water supply under test in the chamber with the tablet added with the standard colors on the vessel.

Microbial Quality Determination

Utilizing a range of standard techniques, the bacteria (Escherichia coli, Salmonella, Shigella, total heterotrophic bacteria, total coliforms, and fecal coliforms) were analyzed, followed by enumeration using most probable number (MPN) and total colony count (TCC) techniques.

Determination of Total Colony Count (TCC) of Total Heterotrophic Bacteria

Total Colony Count (TCC) of total heterotrophic bacteria was determined using the pour plate method. Thiosulphate citrate bile salt sucrose agar (TCBS Agar), was poured into the Petri dishes containing 1mL of the appropriate dilution for the isolation of the total heterotrophic (Ezeet al., 2015).

Determination of Total Coliform and E. coli Count

The water sample was filtered through a 0.45 µm membrane. The inoculated into MacConkey agar. E. coli test plates underwent a 24 h incubation period at 44°C in MacConkey agar. The colonies grown on MacConkey agar were presumptive E. coli. These colonies were then sub-cultured onto Eosin-methylene blue (EMB) agar to confirm the identification (Wamyilet al., 2023).

Enumeration of Total Coliforms

Total coliforms were enumerated using the most probable number (MPN) technique. A three-tube assay was set up, with each tube containing 10 mL of lactose broth. The water sample was added to the tubes in increasing dilutions, and the tubes were incubated at 37°C for 24–48 h. Then they were examined for acid and gas production, and the total coliform counts were estimated using the MPN table. Colonies of the spread plate cultures were directly counted (only plates having 30–300 colonies) and recorded as a function of colony forming units per milliliter (cfu/mL) using the following formula (Wamyilet al., 2023):

$$\begin{array}{r}=\frac{Coloniescounted}{volumeplated}\times Dilutionfactor\end{array}$$

Identification of Fecal Coliform

The membrane filtration technique standard method by APHA, was used for the identification of fecal coliform in swimming pool waters. The membrane, which was used for the filtration, was placed on the Membrane Lauryl Sulphate (MLS) media culture on the Petri dish, which was then put into sterile Petri dishes. Then, the Petri dishes were incubated at a temperature of 44°C ± 0.5°C for fecal coliforms identification. After 24 h, colonies with yellow and pink colors were counted (Payuset al., 2018).

Which gave a total coliform colony-forming unit (c.f.u) per 100 mL of the sample.

Determination of Salmonella and Shigella

1 ml of swimming pool water was added to a test tube containing 10 ml of sterile peptone water and then incubated overnight. Then, 1 mL of the mixture was enriched in Rappaport-Vassiliadis enrichment broth for 24 h. The enriched sample was then streaked onto xylose lysine deoxycholate (XLD) agar, and the presumptive colonies were further confirmed using Analytical Profile Index (API)-20E (Wamyilet al., 2023).

Management of Swimming Pool Water

Using questionnaires, sixteen (16) swimming pool operators were asked about their awareness of hygiene practices and whether they had received any training about swimming pool management.

Data Analysis

The data was analyzed using SPSS (version 21). A one-way analysis of variance (ANOVA) was used to determine significant differences (p ≤ 0.05) between the Swimming pools.

Result and Discussion

Physico Chemical Parameters

pH Determination

Generally, the result of the current study shows that 68.5% (N = 11/16) of swimming pool water fell outside the WHO-recommended limit of pH for pool water, which is 7.2 to 7.8. This implies that the majority of pool water did not comply with the WHO accepted limits of pH. Furthermore, 62.5% (N=10/16) of the swimming pool water samples tested fell below the WHO-recommended ranges of pH values of 7.2, while 6.3% of the samples exhibited pH values that were higher than the WHO-recommended range of 7.8. The sample had an average pH of 6.9. where a mean pH value of 7.4 was discovered. The pH of this study ranged from 6.0 to 7.9. The results are similar to a study conducted in Israel by Natnaelet al. (2024) in which the pH levels of all the swimming pools studied ranged from 6 to 8, and 68.75% of samples had values that were outside the WHO-recommended limit. pH levels in swimming pool water have critical implications for both safety and comfort, affecting water quality and the physical well-being of swimmers (Fig. 2).

Fig. 2. pH of swimming pool water in comparison with the WHO acceptable limits.

Residual Chlorine

Generally, the findings of this study discovered that 31.25% (N = 5/16) had readings outside the WHO’s recommended range (0.2 mg/l–0.5 mg/l). But most had residual chorine with an acceptable range. The residual chlorine levels of two samples typically fell between 0.1 and 0.7 mg/l. This implies that 12.5 % (N = 2/16) of water samples were below the WHO’s recommended range of residual chlorine, and three samples, 18.8% (n=3/16) of the swimming pool water, had residual chlorine concentrations between 1.1 mg/l and 1.4 mg/l, which is above 0.5 mg/l WHO’s minimum recommended limit. The result of residual chlorine was statistically significant at p<0.05 among all the sampled swimming pools (Fig. 3). The findings are in agreement with the study by Yedemeet al. (2017) found that most of the samples were within an acceptable range. These findings were lower than those of the study conducted in Addis Ababa, Ethiopia, which discovered that the Majority 75% (n = 45/60) of the swimming pool water samples had residual chlorine values outside the WHO recommended limit. Furthermore, the observed chlorine residue concentration that was outside the WHO value is in line with investigations by Hoseinzadehet al. (2013). These studies implied that the residual chlorine levels in most swimming pools were not closely monitored. Under application of chlorine will help microorganisms to thrive in the water, and over-application may lead to toxic effects on swimmers (Allenet al., 2004) (Fig. 3).

Fig. 3. Residual chlorine of swimming pool water in comparison with WHO acceptable limits.

Temperature

Overall, 100% (n = 16/16) of swimming pool water had the temperature within the WHO acceptable ranges of 21°C–32°C. According to the study, temperature readings for swimming pool water samples ranged from 25.31°C to 27.82°C. In this study, the findings regarding temperature showed that swimming pool water samples had an average temperature of 25.3°C–27.8°C. The result of temperature was statistically significant at p < 0.05 among all the swimming pools. This number is within the range recommended by WHO for swimming pool water temperature. This result was very comparable to the findings of a study by Rastiet al. (2012), whose value ranged from 24.6° to 26.8°. This suggests that steps were taken to keep track of the swimming pool water’s temperature. Temperature directly impacts the growth and survival of microorganisms. For example, warmer temperatures can accelerate the growth of bacteria and viruses, which can lead to spoilage, contamination, and disease outbreaks.

Turbidity

Overall, 100% (16/16) of swimming pool water samples had a turbidity value within the WHO acceptable limit of (2.5 NTU–7.0 NTU). (Table I). The results of turbidity were statistically significant at p < 0.05. This study was different from the study conducted by Saba and Tekpor (2015), where the Nephelometric Turbidity Unit of swimming pool water ranged from 1.1 NTU–1.7 NTU. All of the samples were below the WHO-recommended level, ranging from 2.5 NTU–7.0 NTU. Turbidity measures the degree to which water loses its transparency due to the presence of suspended particles, including sediments, organic matter, and microorganisms. Conversely, high turbidity often indicates an increased risk of microbial contamination, as bacteria, viruses, and parasites can attach to suspended particles. This can make water unsafe for swimming; then again, turbidity can interfere with water treatment processes. For example, in chlorinated water, suspended particles can shield microorganisms from disinfectants, making it more difficult to achieve effective disinfection.

Table I. Physicochemical Parameters of Swimming Pool Water and Compliance with WHO Standards

SN.	Swimming pool code	Temp(°C)	pH	Turbidity (NTU)	Residual chlorine (mg/l)	p-Value
1	SP1	26.52	6.41	0.56	0.26	0.00001
2	SP2	27.84	6.22	0.65	0.28
3	SP3	25.31	6.97	0.74	0.36
4	SP4	26.73	7.34	1.88	0.65
5	SP5	26.68	7.19	1.57	0.23
6	SP6	26.80	7.90	0.86	0.22
7	SP7	25.91	6.00	1.77	0.73
8	SP8	26.43	6.33	1.77	0.11
9	SP9	25.62	6.72	0.61	0.45
10	SP10	27.62	7.43	0.69	0.33
11	SP11	26.11	7.16	0.61	0.24
12	SP12	26.60	6.92	1.33	0.35
13	SP13	27.16	7.84	1.34	0.14
14	SP14	26.66	6.60	0.89	0.33
15	SP15	25.80	6.72	1.45	0.14
16	SP16	27.82	7.12	0.67	0.37
	WHO Acceptable limit	21-32	7.2-7.8	2.5 – 7.0	0.2-0.5

Microribial Quality

Total Colony Count (TCC) Values of Total Heterotrophic Bacteria

The findings of this study showed that the TCC values of water samples ranged from 5 × 10¹ to 3.9 × 10² before the pools have been filled and 1.9 × 10² to 6.5 × 10² after the pools had been filled. This signifies that before the pools were filled, 50% of the water samples had TCC levels above the WHO-recommended level of (≤200 cfu/ml), indicating that half of the water samples that were expected to be filled in the pools had already exceeded safe bacterial levels. After the pools were filled, 87.5% (n=14/16) of the water samples had TCC levels above the WHO-recommended range of >200 cfu/ml, as for water samples taken after being filled in a pool, there was a clear increase in bacterial count levels. The rise in bacterial count indicates possible contamination during pool use (Table II). The results are in compliance with the research done by Akeju and Awojobi (2015). The results are also concurrent with the study by Adili and Eruteya (2024) found that the total heterotrophic bacterial count ranged from 3.80 log10cfu/ml to 4.76 log10cfu/ml, so this also revealed that the examined swimming pools have not met the World Health Organization (WHO) standard for recreational waters. The result of the Total heterotrophic bacterial count in water before and after being filled. The results among swimming pools are not statistically significant (p > 0.05). The study is also similar to the one done in Kampala, Uganda by Ekopaiet al. (2017) which found that heterotrophic bacterial load contamination was 69.2% of which signifies that swimming pools were highly contaminated and did not conform standards of recreational water quality. The result of Ekopaiet al. (2017) found a different result from the current study that no positive results were yielded for total heterotrophic bacterial counts. This result also contrasts with that by Payuset al. (2018) which depicted much lower contamination levels.

Table II. Total Heterotrophic Bacterial Count of Water Before and After Filling the Swimming Pools

S/N	Sample code	TCC before filled in pool (cfu/ml)	TCC after filling in pool (cfu/ml)	p-value
1	SP1	2.0 × 101	3.3 × 102	0.024296
2	SP2	1.2 × 102	2.3 × 102
3	SP3	1.7 × 102	2.1 × 102
4	SP4	2.2 × 102	3 × 102
5	SP5	3.9 × 102	4.6 × 102
6	SP6	5.0 × 101	6.5 × 102
7	SP7	1.7 × 102	1.9 × 102
8	SP8	1.4 × 102	1.9 × 102
9	SP9	2.5 × 102	3.1 × 102
10	SP10	3.0 × 101	4. 2 × 102
11	SP11	2.2 × 102	3.9 × 102
12	SP12	1.0 × 102	2.1 × 102
13	SP13	3.2 × 102	4.6 × 102
14	SP14	2.2 × 102	3.0 × 103
15	SP15	2.5 × 102	2.6 × 103
16	SP16	1.9 × 102	2.7 × 102

Coliform Counts in MPN Values

Before filling the water into the pool, a substantial portion of the water samples (75%) had total coliform counts above the WHO-recommended limit (MPN > 2/100 ml), indicating that the pool water maintenance practices prior to filling were already compromised. Only 25% of the samples were within the acceptable range, suggesting that before being filled, the water may not have been adequately treated with chlorine to kill the microbes. After the pools were filled and used, the percentage of samples exceeding the recommended limit decreased slightly to 56.3% which may be because of chlorination. While this is an improvement, it still indicates that more than half of the pool water samples had coliform levels that exceeded safe limits, an indication of significant health risk to swimmers. Only 43.8% had a total coliform count that was over the permissible threshold. The result of coliform counts in MPN value is non-significant between the swimming pools (p>0.05) (Table III). The study by Saba and Tekpor (2015) backs up this claim. The results, however, fell short of the study’s conclusion (Yedemeet al., 2017).

Table III. Most Probable Number of Coliform in Swimming Pool Water (< 2 MPN/100 ml)

SN.	Sample code	Before filled and bath MPN/100 ml	After filled and bath MPN/100 ml	p-value
1	SP1	0.6 × 101	1.4 × 101	0.431667
2	SP2	1.2 × 101	0.9 × 101
3	SP3	0.5 × 101	1.3 × 101
4	SP4	1.8 ×101	3.2 × 101
5	SP5	2.0 × 101	4.4 × 101
6	SP6	0.4 × 101	0.6 × 101
7	SP7	1.5 × 101	2.9 × 101
8	SP8	2.5 × 101	3.8 × 101
9	SP9	0.6 × 101	0.9 × 101
10	SP10	4.6 ×101	2.4 × 101
11	SP11	1.9 × 101	2.5 × 101
12	SP12	6.2 × 101	8.3 × 101
13	SP13	1.7 × 101	0.8 × 101
14	SP14	0.6 × 101	0.8 × 101
15	SP15	0.8 × 101	0.3 × 101
16	SP16	1.0 × 101	1.6 × 101

Fecal Coliform Count

E. coli was found in two samples with a detection rate of 12.5% (n=2/16), while Salmonella and Shigella were not detected in any water sample. Detection of E. coli in 12.5% of the samples is a concern because it indicates that fecal contamination has occurred in the pools. The result was in lower rate compared to the study by Ekopaiet al. (2017), which showed that more than two swimming pool water samples had E. coli contamination. Since E. coli should not be present in swimming pools, according to WHO criteria, 12.5% of the pool water in this experiment did not meet the necessary requirements. The study also concurs with the one done in Natnaelet al. (2024), which recorded High counts of 68% of fecal coliforms. Additionally, in Nigeria, all pool water samples were polluted with fecal coliforms (Ayandeleet al., 2015). The result also contradicts the standard recommended values and consequently affects the health of the swimming pool users. The presence of coliforms, especially FC, in swimming pools indicates fecal contamination.

Bacterial Quality in Compliance with WHO Acceptable Limits

As far as the results are concerned, the bacteriological quality assessment of swimming pool water indicated that about 7 (43.7%) swimming pools complied with the WHO, while 9 (56.3%) did not comply with the WHO acceptable limit of total coliform bacteria counts. Based on heterotrophic bacterial count, 14 (77.5%) were in compliance with the WHO, while only 2 (12.5%) were not in compliance with the WHO acceptable limits. Shigella and Salmonella were not detected in any of the water samples, but only 2/16 (12.5%) swimming pool water samples were found to be contaminated with E. coli. Even though the proportion is relatively low, E. coli is a strong indicator of the potential presence of other harmful pathogens, such as viruses, parasites, or more dangerous bacteria in the pool water that can cause illnesses ranging from mild to severe gastroenteritis (Table IV).

Table IV. Microbiological Quality with Respect to WHO Standards

Parameter	Number swimming pool	Compliedwith WHO	Not complied with WHO
Total Coliform count (< 1 MPN/ml)	16	7 (43.7%)	9 (56.3%)
Heterotrophic bacteria (c.f.u/ml<200)	16	14 (77.5%)	2 (12.5%)
Salmonella (<1/100 ml)	16	Acceptable	None
Shigella (<1/100 ml)	16	Acceptable	None
E.coli (0/100ml)	16	14 (87.5%)	2 (12.5%)

Awareness of Hygiene Practices and Attendance in Training about Swimming Pool Management

Overall, on awareness about the hygiene practices of swimming pools. The findings elucidated that 68.8% of respondents had no awareness of hygiene practices and sanitation issues. That is to say, pool staff members may put swimmers at risk of infections if they lack proper hygiene practices.

Furthermore, the study’s results found that 87.5% of swimming pool operators did not attend training about swimming water treatment (Fig. 4).

Fig. 4. Levels of awareness and attendance in pool management training.

The result differs from to study by Bathija and Narasimha (2019) demonstrated that the majority of swimming pool operators had knowledge about swimming pool management.

Conclusion and Recommendation

The study findings revealed that the swimming pools water did not adequately meet the WHO physico-chemical standards for temperature and turbidity. The microbiology of most swimming pool water did not adequately comply with the WHO. Furthermore, the study result portrayed that there was inadequate commitment of hotels’ owners as most of them did not provide training about swimming pool management to their pool operators, which resulted a significant impact on poor swimming pool water quality, which is a risk to the health of swimmers. To improve swimming pool water quality, there is a need for pool water monitoring through government regulatory institutions.

Acknowledgment

The authors would like to thank the head of laboratory services, Zanzibar Food and Drug Agency (ZFDA), Khadija Ali Sheha, for the assistance in the analysis of the sample at the ZFDA Laboratories.

Conflict of Interest

Authors declare no conflict of interest.