Assessing drinking water quality in the city of Kenge, Democratic Republic of the Congo Open Access

Outbreaks of waterborne diseases, such as typhoid fever, hepatitis, and dysenteric diarrhea, have been consistently increasing over the years and severely impinging public health in Kenge City. The population uses river water and groundwater as drinking water and for other domestic uses. A drinking water quality assessment was conducted in the municipality. Physicochemical and bacteriological analyses of water, including the determination of T, pH, electrical conductivity, O₂, total dissolved solids (TDS), soluble ions, were carried out on 20 water samples collected in the Soussa and Maniéka Rivers, in Kikobo spring, and in two water boreholes, which are the main drinking water supply sources for the municipality. Samples from tap water distributed by the public water company were analyzed also. The results of this assessment revealed that T, pH, O₂, and TDS in water during both the dry and wet seasons generally exceeded the limits set by WHO for drinking water quality. Escherichia coli and Enterococcus were observed in groundwater samples from boreholes and from the Kikobo spring, while total coliforms were identified in all samples, including those from the public water distribution network. These results explained the increasing trends of waterborne diseases observed in the region.

Waterborne diseases are prevalent in many parts of the world and pose a major health risk to the human populations. This occurs particularly in developing countries lacking sanitary infrastructures and relying on the use of untreated surface waters as drinking water (WHO 2017; Fazal-ur-Rehman 2018).

According to the World Health Organization (WHO 2011, 2018, 2019), 60% of the world population does not have access to reliable sanitation, 30% does not have access to safe drinking water, and about 2 billion people consume water from sources contaminated with fecal matter. The consumption of water from such sources has been associated with the occurrence of diseases such as diarrhea, cholera, hepatitis A, typhoid fever, and polio (WHO 2011; Nienie et al. 2017; Kapembo et al. 2022). Worldwide, a prevalence of about 4 billion cases of diarrhea is observed every year, and it is due to a lack of safe drinking water, sanitation, and hygiene. Approximately 1 million diarrhea-related deaths are recorded each year in developing countries, most of which are children under the age of five (Fawell & Nieuwenhuijsen 2003; Mwanamoki et al. 2015; Tongesayi & Tongesayi 2015; Kapembo et al. 2016, 2022; Nienie et al. 2017). The consumption of water is responsible for such an impact on human health, and this is because water sources are contaminated with untreated sewage, wastewater from hospitals, industries, mines, and urban runoff contaminated by waste from anthropogenic activities. Furthermore, surface waters and groundwater are often contaminated with fecal bacteria originating from the practice of open-field defecation and lack of sewage collection and proper treatment (Thevenon et al. 2012; Mwanamoki et al. 2014; Kilunga et al. 2016; Barnett et al. 2018; Pakasi 2018; Atibu et al. 2022, 2023; Lin et al. 2022).

In the Democratic Republic of the Congo (DRC), despite the abundance of freshwater, more than three-quarters of its population, recently estimated at about 70 million, do not have access to safe drinking water, and this is further exacerbated by the rapid population growth (UNEP 2011).

Previous studies conducted in the DR Congo, specifically in Kinshasa and Kikwit cities on epidemiology and drinking water quality, have shown a prevalence of waterborne diseases such as typhoid fever, amebic dysentery, gastroenteritis disorders, and cholera. The water sources investigated in these cities showed high contamination by fecal indicator bacteria (FIB), including Escherichia coli (E. coli), Enterococcus (ENT) and total coliforms (TC) (Kapembo et al. 2016, 2022; Nienie et al. 2017). Many other regions in the DRC may suffer similar contamination of water resources and identical threats to public health, but water research and the monitoring of water quality are lacking throughout the country.

The current study was carried out in the municipality of Laurent-Désiré Kabila, city of Kenge, province of Kwango, in the DRC. This province has faced recurrent outbreaks of waterborne diseases, such as typhoid fever. This study was the first investigation in this region on the prevalence of waterborne diseases and the first assessment of the quality of water from the main supply sources.

The majority of the population uses surface water from the rivers Maniéka and Soussa and groundwater from boreholes as drinking water and water for other domestic uses (cooking and bathing). Several springs are available in the area, and their water is used by a small fraction of the population. The national water treatment and distribution agency, called ‘Régie de distribution d'eau’ (REGIDESO), also dispenses drinking water at several free-of-charge distribution points (public taps) in the municipality (Figure 2).

The physicochemical and bacteriological parameters to be determined in water sources were selected in accordance with the WHO guidelines for monitoring drinking water quality (WHO 2017). The evaluation of the physicochemical quality of water included the determination of water temperature, pH, electrical conductivity, dissolved oxygen, total dissolved solids, dissolved ions, and the identification and enumeration of microorganisms, including, E. coli, ENT, and TC in water, as described in the following.

For the assessment of the prevalence of waterborne diseases in the study area, secondary data were used. These data were obtained from the central office of the Kenge health zone and are based on the annual attendance reports of the sick population in four health facilities from 2016 to 2020. The health facilities were the Kenge General Hospital of Reference, the Centre de Santé «Barrière», the Centre de Santé «Référence», and the Centre de Santé «Jumeaux».

A total of 10 sampling points, all used by the population for water provision, were selected for the collection of water samples. The global positioning system (GPS) locations of the sampling points are shown in Table 1.

These sampling points encompassed two rivers (Maniéka and Soussa, with three sampling points each), two boreholes (Barrière and Mangangu, respectively, with 15 and 30 m depth), a spring source (Kikobo), and a public tap from the REGIDESO public water distribution network. The water sampling was carried out during the dry season (August) and repeated in the rainy season (November) in 2022.

At each sampling point, the water physical-chemical parameters were determined in situ with a portable probe. Triplicate samples of about 500 mL each were collected directly into 1 L sterile polyethylene bottles for dissolved ions analysis. In the rivers, water samples were taken at about 1 m from shore and 20–30 cm deep, with caution to avoid suspending the bottom sediments. All samples for dissolved ion analysis were stored in a 4 °C cooler and transported to the laboratory for analysis. Additional samples for microbiological analysis were collected, in triplicate, directly into sterile plastic bottles and stored in a 4 °C cooler. These samples were immediately transported to the Microbiology Laboratory of the University of Kinshasa, and the analyses were carried out within 24 h.

The water samples were labeled as follows: (1) RM1, RM2, and RM3 for the Maniéka River; (2) RS1, RS2, and RS3 for the Soussa River; (3) F1 and F2 for Mangangu and Barriere boreholes, respectively; (4) SK for the Kikobo spring source; and (5) for the tap water provided by REGIDESO to the population (Table 1).

Physicochemical parameters of water, including temperature (T), hydrogen potential (pH), dissolved oxygen (O₂), electrical conductivity (EC), and total dissolved solids (TDS) were determined in situ using a 340i multiparameter probe (WTW, Weilheim, Germany), calibrated by the manufacturer.

The concentrations of dissolved ions phosphate ⁠, sulfate ⁠, nitrate ⁠, calcium (Ca²⁺), magnesium (Mg²⁺), and chloride (Cl⁻) were determined by ion chromatography (Dionex ICS-3000, Canada) according to the method described by Graham et al. (2014). Specific chromatographic columns (Thermo Fisher Scientific) were used for cations and anions.

As an analytical quality control procedure, a water-certified reference material (CRM) (Ontario-99, Water Research Institute, Canada) was used to verify the instrument's accuracy. The CRM results were within the 95% acceptable range of values issued on the CRM certificate (Mavakala et al. 2016; Kapembo et al. 2022).

The bacteria, including E. coli, ENT, and TC, were quantified in water samples using the membrane filtration method (Nienie et al. 2017; Kapembo et al. 2022). In brief, water samples were passed through a 0.45 μm filter (47 mm diameter, Millipore, Bedford, USA) and placed on different selective culture media (Biolife, Italia) supplemented with the antifungal compound Nystatin (100 μg mL⁻¹ final concentration), using the following incubation conditions: E. coli: Tryptone Soy Agar (TSA) medium, incubated at 37 °C for 4 h and transferred to Tryptone Bile X-Gluc Agar medium at 44 °C for 24 h; ENT: Slanetz Bartley Agar medium, incubated at 44 °C for 48 h and transferred into Bile Aesculin Agar medium at 44 °C for 4 h; TC: Endo Agar, incubated at 35 °C for 24 h. The results were expressed as colony-forming units per 100 mL of water (CFU.100 mL⁻¹).

The reproducibility of the whole bacteriological experimental procedure was tested by means of triplicate analysis of selected samples. The results of triplicate analyses displayed a mean coefficient of variation of 8% for E. coli and TC and 9% for ENT, which is considered acceptable (APHA 2005).

All measurements and analyses were conducted in triplicate for each sample. SigmaStat 11.0 (Systat Software, Inc., USA) and XLSTAT software from Addinsoft (2020) (Statistical and data analysis solution. New York, United States, https://www.xlstat.com) were used to perform statistical data treatment.

Table 2 displays the frequency of waterborne diseases recorded in four primary health centers of the study area over a 5-year period, from 2016 to 2020. The population does not frequently visit hospitals due to budgetary constraints, except in severe cases. As a result, the information gathered is not fully representative of the public health conditions, and it is an underestimation of illness cases, but it is the only information available.

Overall, the number of cases of waterborne illnesses increased steadily over the years, and it was multiplied by a factor of 3–7.5 in the 5-year period, constituting an alarming situation. The ramp-up of the number of cases is an indication that the contamination of water sources expanded dramatically over the years.

In general, the main cause of the increase in the number of cases of waterborne diseases is the lack of access to safe drinking water (Podewils et al. 2004; Ugboko et al. 2020). Previous studies in Democratic Republic of the Congo (DRC) demonstrated a prevalence of waterborne diseases, including diarrhea, gastroenteric disorders, typhoid fever, amebic dysentery, and cholera, particularly in the localities of Mont-ngafula, Selembao, and Kimbaseke, all located in the Kinshasa metropolitan area (Kapembo et al. 2019, 2022).

This study was performed to take into account the potential seasonal variation of water parameters round the year. The values of physicochemical parameters measured on water samples (T, pH, EC, O₂, and TDS) in both dry and wet seasons are presented in Table 3. Therein, these parameter values are compared with the water quality guidelines issued by the WHO for drinking water (WHO 2017).

Regarding the water temperature, it was observed that only the samples RM3 (26.1 °C), S1 (25.6 °C) and F1 (25.2 °C) deviated during the dry season from the range of temperature values recommended by WHO (12–25 °C) while for the wet season, most samples showed values above 25 °C, except the samples RM2 (24.2 °C) and F2 (24.7 °C). The water sample of «REGIDESO», collected for comparison, displayed a temperature value of 25.6 °C (wet season) and 24.6 °C (dry season). These results are comparable with those published for tropical conditions by Nienie et al. (2017) (ranging from 24.5 to 25.6 °C in the wet season and from 24.7 to 29.2 °C in the dry season) and Kapembo et al. (2022) (ranging from 25.8 to 28.8 °C in the wet season and from 23.9 to 26.9 °C in the dry season).

All samples displayed acid pH values for both seasons, ranging from 4.49 to 5.10 in the dry season, and from 4.49 to 5.25 in the wet season. The «REGIDESO» water samples also showed an acidic pH of 4.43 (dry season) and 5.77 (wet season). These values were below the WHO-recommended pH range of 6.5–9.5. Similar findings were also made by Kapembo et al. (2022), who reported pH values ranging from 4.6 to 7.8 in the wet season and from 5.2 to 6.9 in the dry season in the Kinshasa metropolitan area. As explained in our previous studies performed in similar environments (e.g., Kapembo et al. 2016; Nienie et al. 2017), several parameters, including acid rain in the studied location, natural rock formations, landfills, organic matter decomposition, the presence of animal farms, and chemical runoff from agricultural fields, can explain the causes of poor water physicochemical parameters, especially low pH.

The EC of water varied in the range of 215–296 μS cm⁻¹ in the dry season and in the range of 201–281 μS cm⁻¹ in the wet season. These values were within the range of the WHO drinking water quality standards (200–800 μS cm⁻¹). The «REGIDESO» sample displayed a value of 465 μS cm⁻¹ (dry season) and 180 μS cm⁻¹ (wet season).

The dissolved oxygen (O₂) generally displayed values between 4 and 6 mg L⁻¹, the range of values recommended by the WHO. However, several water samples displayed values outside the recommended range.

For the TDS parameter, only one water sample, Kibibobo Spring (S1), displayed the value of 0 mg L⁻¹, in agreement with the recommended value of WHO. All other samples showed values above 0 mg L⁻¹, ranging from 0.12 to 70.70 mg L⁻¹ (dry season) and from 0.15 to 72.70 mg L⁻¹ (wet season). Mangangu borehole and Barrière borehole water samples, and both Soussa and Maniéka Rivers displayed very high TDS values, namely those for Maniéka River, which also displayed low O₂ content in dry and wet seasons, suggesting the presence of high amounts of organic matter and stagnant water.

The concentrations of dissolved ions ⁠, ⁠, Cl⁻, ⁠, Ca²⁺_, and Mg²⁺ in water samples are shown in Table 4. In general, during the dry and wet seasons, the ion concentrations in water samples met the values recommended by the WHO guidelines for drinking water quality (WHO 2017). There were some exceptions, especially for which varied from 4.23 to 45.7 mg L⁻¹ during the dry season and from 4.25 to 35.8 mg L⁻¹ during the wet season, and for Mg²⁺ in sample RM3 (with 54.2 mg L⁻¹) during the dry season.

Table 4

Concentrations of dissolved ions in water samples (mg L⁻¹) collected in dry and wet seasons

.	Sampling site .	.		.		Cl− .		.		Ca2+ .		Mg2+ .
Site .	Season .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .
Soussa River	RS1	25.4	21.9	16.2	15.3	3.8	3.52	6.7	6.8	118.3	102.5	46.1	41.4
	RS2	17.3	13.2	17.5	14.3	4.21	3.48	6.1	7	109.6	66.64	34.5	31
	RS3	45.7	35.8	16.3	15.1	3.64	2.14	5.3	5.8	72.16	65.25	32.7	28.5
Maniéka River	RM1	12.5	10.5	12.3	10.5	3.8	3.12	6.7	6.8	132.7	128.6	24.4	21.1
	RM2	26.8	14.2	17.4	15.3	4.8	3.73	3.4	3.5	115.2	116.7	32.4	26.8
	RM3	31.3	18.3	15.4	13.7	3.8	3.57	5.8	5.9	121.3	111.4	54.2	44.4
Kikobo spring	S1	6.74	4.25	9.18	7.4	3.8	3.86	1.1	1.1	26.78	21.61	20	16.3
Mangangu borehole	F1	4.23	4.5	4.06	3.14	9.56	7.46	3.5	3.6	17.25	4.41	13.7	11.5
Barrière borehole	F2	8.47	6.47	4.75	4.7	12.4	10.4	7.6	7.7	19.11	6.82	25.2	22.2
REGIDESO		9.13	8.65	4.15	4.1	13.4	12.4	4.4	4.5	32.49	33.4	18	6.03
WHOa		≤0.5	≤0.5	50	50	250	250	500	500	270	270	50	50

.	Sampling site .	.		.		Cl− .		.		Ca2+ .		Mg2+ .
Site .	Season .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .	Dry .	Wet .
Soussa River	RS1	25.4	21.9	16.2	15.3	3.8	3.52	6.7	6.8	118.3	102.5	46.1	41.4
	RS2	17.3	13.2	17.5	14.3	4.21	3.48	6.1	7	109.6	66.64	34.5	31
	RS3	45.7	35.8	16.3	15.1	3.64	2.14	5.3	5.8	72.16	65.25	32.7	28.5
Maniéka River	RM1	12.5	10.5	12.3	10.5	3.8	3.12	6.7	6.8	132.7	128.6	24.4	21.1
	RM2	26.8	14.2	17.4	15.3	4.8	3.73	3.4	3.5	115.2	116.7	32.4	26.8
	RM3	31.3	18.3	15.4	13.7	3.8	3.57	5.8	5.9	121.3	111.4	54.2	44.4
Kikobo spring	S1	6.74	4.25	9.18	7.4	3.8	3.86	1.1	1.1	26.78	21.61	20	16.3
Mangangu borehole	F1	4.23	4.5	4.06	3.14	9.56	7.46	3.5	3.6	17.25	4.41	13.7	11.5
Barrière borehole	F2	8.47	6.47	4.75	4.7	12.4	10.4	7.6	7.7	19.11	6.82	25.2	22.2
REGIDESO		9.13	8.65	4.15	4.1	13.4	12.4	4.4	4.5	32.49	33.4	18	6.03
WHOa		≤0.5	≤0.5	50	50	250	250	500	500	270	270	50	50

^aLimit recommended by WHO Guidelines for Drinking-water Quality (WHO 2017).

Note. In bold, values not in agreement with the water quality guidelines recommended by the WHO.

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The water samples from the Soussa and Maniéka Rivers displayed high concentrations of dissolved ions when compared with the Kikobo spring and Mangangu and Barrière boreholes during the dry and wet seasons. The high concentrations of phosphate ions in water likely were, at least in part, a result of organic matter decomposition in surface waters, but their presence in groundwater from boreholes seems to indicate also a geological source of phosphate ions.

In general, the dissolved ion concentration values were higher in the dry season than in the wet season, which is due to the dilution effect of the more abundant water flows occurring in the wet season.

For the three FIB groups, the highest concentrations occurred during the wet season, which points out that, following rains, the surface runoff and overflow of pit latrines are the likely vehicles for bacterial contamination of water supply sources. This is in agreement with results from previous reports from developing countries in tropical regions (Kapembo et al. 2016, 2019, 2022; Nienie et al. 2017).

The water from the two boreholes (F1 and F2), the spring source (S1), and the water from REGIDESO, supposedly treated, displayed better conditions for E. coli and ENT than surface waters from rivers. However, all of them were contaminated with TC.

The high values of microbial concentrations observed at the RS3 site were confirmed to be caused by runoff from households and during the rainy season, more specifically, by latrine water discharges occurring upstream of the sampling site. In general, the Laurent-Désiré Kabila municipality lacks infrastructures for residential waste collection and sanitation facilities, such as the sewers network, which are at the root of this widespread microbial contamination of water bodies.

Spearman correlation tests between the physicochemical and bacteriological parameters evaluated in this study were performed for both dry and wet seasons (Table 5A and B).

Table 5

Spearman correlation of physicochemical and bacteriological parameters during the (A) dry season and (B) wet season

A .	T .	pH .	EC .	O2 .	Ca2+ .	Mg2+ .	.	.	.	Cl− .	ENT .	CT .	TDS .
Ca2+	− 0.665	−0.102	− 0.536	− 0.85
Mg2+	−0.269	−0.128	− 0.605	− 0.671	0.72
	0.106	−0.336	−0.362	− 0.746	0.542	0.696
	−0.403	−0.332	− 0.603	− 0.94	0.851	0.747	0.761
	−0.075	0.068	−0.203	−0.269	0.394	0.436	0.22	0.176
Cl−	0.516	0.139	0.748	0.785	− 0.714	− 0.561	− 0.561	− 0.848	0.08
ENT	− 0.797	0.263	−0.338	−0.406	0.708	0.176	0.165	0.459	0.069	−0.492
CT	0.387	−0.237	−0.107	−0.32	−0.033	−0.055	0.616	0.309	−0.022	−0.274	0
TDS	−0.43	−0.178	− 0.579	− 0.924	0.941	0.777	0.775	0.928	0.388	− 0.761	0.582	0.25
E. coli	0.362	−0.314	−0.092	−0.446	0.115	0.153	0.806	0.433	−0.059	−0.351	0.056	0.935	0.405
B .	T .	pH .	EC .	O2 .	Ca2+ .	Mg2+ .	.	.	.	Cl− .	ENT .	CT .	TDS .
Ca2+	0.677	−0.096	−0.56	−0.748
Mg2+	0.393	−0.526	−0.031	−0.752	0.64
	0.383	−0.589	0.144	−0.784	0.461	0.598
	0.362	−0.567	−0.071	−0.938	0.791	0.814	0.745
	0.272	0.01	0.064	−0.367	0.298	0.473	0.338	0.275
Cl−	−0.449	0.765	−0.063	0.756	−0.644	−0.639	−0.542	− 0.814	0.007
ENT	0.695	−0.118	−0.358	−0.398	0.771	0.197	0.276	0.538	−0.006	−0.577
CT	0.222	−0.633	0.541	−0.361	0.035	0.079	0.733	0.365	0.05	−0.391	0.288
TDS	0.57	−0.422	−0.208	−0.924	0.898	0.818	0.724	0.947	0.423	−0.769	0.598	0.284
E. coli	0.138	−0.586	0.451	−0.49	0.125	0.129	0.789	0.478	0.014	−0.414	0.292	0.966	0.378

A .	T .	pH .	EC .	O2 .	Ca2+ .	Mg2+ .	.	.	.	Cl− .	ENT .	CT .	TDS .
Ca2+	− 0.665	−0.102	− 0.536	− 0.85
Mg2+	−0.269	−0.128	− 0.605	− 0.671	0.72
	0.106	−0.336	−0.362	− 0.746	0.542	0.696
	−0.403	−0.332	− 0.603	− 0.94	0.851	0.747	0.761
	−0.075	0.068	−0.203	−0.269	0.394	0.436	0.22	0.176
Cl−	0.516	0.139	0.748	0.785	− 0.714	− 0.561	− 0.561	− 0.848	0.08
ENT	− 0.797	0.263	−0.338	−0.406	0.708	0.176	0.165	0.459	0.069	−0.492
CT	0.387	−0.237	−0.107	−0.32	−0.033	−0.055	0.616	0.309	−0.022	−0.274	0
TDS	−0.43	−0.178	− 0.579	− 0.924	0.941	0.777	0.775	0.928	0.388	− 0.761	0.582	0.25
E. coli	0.362	−0.314	−0.092	−0.446	0.115	0.153	0.806	0.433	−0.059	−0.351	0.056	0.935	0.405
B .	T .	pH .	EC .	O2 .	Ca2+ .	Mg2+ .	.	.	.	Cl− .	ENT .	CT .	TDS .
Ca2+	0.677	−0.096	−0.56	−0.748
Mg2+	0.393	−0.526	−0.031	−0.752	0.64
	0.383	−0.589	0.144	−0.784	0.461	0.598
	0.362	−0.567	−0.071	−0.938	0.791	0.814	0.745
	0.272	0.01	0.064	−0.367	0.298	0.473	0.338	0.275
Cl−	−0.449	0.765	−0.063	0.756	−0.644	−0.639	−0.542	− 0.814	0.007
ENT	0.695	−0.118	−0.358	−0.398	0.771	0.197	0.276	0.538	−0.006	−0.577
CT	0.222	−0.633	0.541	−0.361	0.035	0.079	0.733	0.365	0.05	−0.391	0.288
TDS	0.57	−0.422	−0.208	−0.924	0.898	0.818	0.724	0.947	0.423	−0.769	0.598	0.284
E. coli	0.138	−0.586	0.451	−0.49	0.125	0.129	0.789	0.478	0.014	−0.414	0.292	0.966	0.378

Note. Physicochemical parameters including: pH, temperature (T), EC, dissolved oxygen (O₂) and soluble ions (Ca²⁺, Mg²⁺, ⁠, ⁠, ⁠, Cl⁻,) and bacteria (E. coli, ENT, and TC). Positive and significant coefficients (p < 0.05) are in bold.

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Positive and significant correlations were observed between T and Cl⁻ (R² = 0.516), EC and Cl⁻ (R² = 0.748), O₂ and Cl⁻ (R² = 0.785) for the dry season, suggesting that Cl⁻ transport is positively influenced by those parameters.

Negative correlations were found between parameters such as T and Ca²⁺ (R² = −0.665), T and ENT (R² = −0.797), EC and Ca²⁺ (R² = −0.536), Mg²⁺ (R² = −0.605), (R² = −0.603), TDS (R² = −0.579); O₂ and Ca²⁺ (R² = −0.85), Mg²⁺ (R² = −0.671), (R² = −0.746), (R² = −0.94), and TDS (R² = −0.924) in the wet season, suggesting a negative influence of T, EC, and O₂ in the transport of those soluble ions and bacteria.

Positive correlations were also observed between Ca²⁺ and Mg²⁺ (R² = 0.72), (R² = 0.542), (R² = 0.851), ENT (R² = 0.708), TDS (R² = 0.941); Mg²⁺ and (R² = 0.696), (R² = 0.747), TDS (R² = 0.777); and (R² = 0.761), CT (R² = 0.616), TDS (R² = 0.775) and E. coli (R² = 0.806); and TDS (R² = 0.928); ENT and TDS (R² = 0.582) and CT and E. coli (R² = 0.935) for the dry season, indicating that, in general, the soluble ions and the bacteria were associated and originated from the same sources.

The negative correlation between Cl⁻ and Ca²⁺ (R² = −0.714), Mg²⁺ (R² = −0.561); (R² = −0.561), (R² = −0.848) and TDS (R² = −0.761) in the dry season suggested different origins and different cycling pathways of Cl⁻ compared to the other dissolved ions. The same trend was observed for the wet season (Table 5B).

This study is the first assessment of the physical-chemical and bacteriological parameters in surface waters from the Soussa and Maniéka Rivers, spring water (Kikobo spring) and groundwater from boreholes (Mangangu and Barrière) in the Laurent-Désiré Kabila municipality of Kenge City, DRC. These water sources provide more than 80% of the water used for domestic purposes, including drinking water for the population. The tap water from the public water distribution network, REGIDESO, was also analyzed.

Results revealed that the water from investigated sources was not suitable as drinking water particularly because of fecal bacteria contamination (E. coli, ENT, and TC). The high and widespread bacterial contamination of these water sources is thus the reason for the outbreaks of waterborne diseases observed in the region.

The water samples collected from surface rivers, spring, and boreholes also showed a high content of dissolved ion, exceeding the concentration limit recommended by the WHO for drinking water quality. For the parameters pH and TDS, the values determined in water samples were also not in conformity with the WHO recommendations. These findings showed that this water, besides contamination by fecal bacteria, is also of poor chemical quality.

Very worrisome was the finding that tap water provided by the water company to the population at public distribution points (taps) is also of non-sufficient quality according to the international water quality guidelines set by WHO. Therefore, the water treatment of the public water company must be improved.

To diminish the impact of waterborne diseases, some urgent measures are needed, such as the supply of safe drinking water to substitute the contaminated water sources in use by the population. Furthermore, in the long run, it is needed to abate contamination of the water sources. However, the quality of traditional water sources may only improve if policies are approved to implement the construction of improved sanitary infrastructures and to spread awareness of good hygienic practices.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.