Waterborne diseases are caused by consuming drinking water contaminated with human or animal feces carrying pathogenic microorganisms such as viruses, bacteria, and protozoa, which are capable of surviving and multiplying in water, food, and on various surfaces. Among the diseases most frequently associated with this contamination are cholera, dysentery (shigellosis and amebiasis), typhoid fever, cryptosporidiosis, giardiasis, cyclosporiasis, yersiniosis, and salmonellosis, which manifest primarily as diarrheal episodes. Other viral gastroenteritis infections (rotavirus, norovirus, adenovirus, enterovirus, calicivirus, astrovirus, reovirus) can also occur [1]. Diarrhea thus remains one of the leading causes of morbidity and mortality worldwide, particularly among children [1].

Globally, waterborne diarrheal diseases remain particularly prevalent in areas where drinking water treatment is inadequate or nonexistent. Consumption of contaminated water, combined with poor sanitation and hygiene, is responsible for approximately 88% of the four billion cases of diarrhea recorded each year, resulting in 1.8 million deaths, nearly 90% of which occur in children under five years of age [2].

In sub-Saharan Africa, and particularly in the Democratic Republic of Congo (DRC), inequalities in access to drinking water disproportionately affect rural populations, who are largely dependent on natural water sources and surface water, thus exposing them more to the consumption of unsafe water. It is estimated that approximately 37 million people living in rural areas of the DRC are at risk of diseases related to the contamination of streams and rivers [3].

Reducing morbidity and mortality from diarrheal diseases relies on implementing interventions that target the interruption of fecal-oral transmission, including access to sufficient quantities of safe water, adequate sanitation, the availability of handwashing facilities, and the promotion of personal and food hygiene practices [1][4]. Among these interventions, household water treatment (HWT) such as solar disinfection (SODIS), boiling, chlorination, filtration, and proper water storage practices are promising alternatives for improving household water security [5].

In the DRC, the rate of drinking water coverage has declined over the past few decades, a consequence of the degradation of existing infrastructure, itself linked to more than twenty years of armed conflict, insufficient investment and sustained population growth [6].

In the province of Haut-Uélé, a study conducted in the Isiro health zone on the physico-chemical and bacteriological quality of water revealed that, out of 23 water points assessed, only 2 (8.7%) provided water that met WHO drinking water standards, free from any indicators of fecal contamination, while 13 water points (56.5%) delivered heavily polluted water, showing 3 to 4 indicators of contamination [7].

In this same province, access to drinking water remains limited: only 24.3% of the population has at least a basic drinking water service [8], while a study conducted in the rural health zone of Isiro estimated the prevalence of diarrhea at 14.57% [9]. Despite the scale of this problem and its health consequences, no large-scale program is currently being implemented to address it [10].

Faced with limited access to conventional disinfection products, harnessing the region’s natural solar potential appears to be a relevant alternative for mitigating the consequences of consuming unsafe water [5][11]. Solar water disinfection (SODIS) is precisely a simple and sustainable water treatment method that uses solar radiation (UV-A and thermal effects) to inactivate pathogenic bacteria and viruses present in water [5]. Although effective and inexpensive, this method remains relatively unknown among the Congolese population in general, and in the Haut-Uélé region in particular [11].

It is in this context that the present study was conducted, with the objective of determining the prevalence of diarrhea in the household and the associated factors.

Water-related morbidity in the households surveyed was characterized by a high prevalence of waterborne diseases, reflecting insufficient access to quality drinking water, precarious hygiene conditions and inadequate sanitation practices among the populations concerned.

Children under five are the most affected group by waterborne morbidity due to their immature immune systems, increased susceptibility to enteric pathogens, and frequent exposure to unsanitary environments. This vulnerability is exacerbated by inadequate hygiene practices and limited access to safe drinking water, contributing to a high incidence of diarrheal diseases and other waterborne infections in this age group.

1) Prevalence of diarrhea:

This study highlights a high prevalence of diarrhea in rural households in Haut-Uélé (43.2% of households reporting at least one case; Table 2), significantly higher than national estimates from demographic surveys in the DRC (14%) [12] and some global estimates reported in low- and middle-income countries [13]. This difference suggests significant intra-national heterogeneity, already documented in several African contexts where isolated rural areas exhibit considerably worse health indicators [13][14].

The prevalence among children under five years of age (15.4%, or 86 out of 560 children identified; Table 2) is consistent with international trends, confirming their increased vulnerability related to immune immaturity, exploratory behaviors, and high environmental exposure [1][13]. Randomized trials, notably in Bolivia, have also documented a high incidence in this age group before intervention [15], while recent meta-analyses confirm that this age group bears the majority of the global burden of diarrheal disease [13][14].

One of the most striking results of our study is the very low proportion of households treating water before consumption (4.2%; Table 1). This level is lower than those observed in several studies conducted in Africa and Asia, where the adoption of home water treatment, although variable, remains more widespread [16][17]. According to Kraemer and Mosler, the adoption of these practices is strongly dependent on behavioral factors, risk perception, and ease of use [11]. Contrary to the evidence from meta-analyses showing a significant reduction in diarrhea with home water treatment [13][14], our study found no significant association between water treatment and diarrhea (OR = 0.99; p = 1.000; Table 3). This discrepancy can be explained by several factors: insufficient statistical power due to the small number of households treating water (n = 14), poor adherence to treatment techniques, variability in the quality of their implementation, or measurement biases, as suggested by some critical reviews focused on adherence to interventions [18].

Water storage for more than 24 hours, observed in 63.7% of households (Table 1), appears to be the determinant most strongly associated with diarrhea in our sample, both in bivariate analysis (OR = 3.25; 95% CI: 1.99 - 5.30; p < 0.0001) and in multivariate analysis after adjustment (aOR = 3.09; 95% CI: 1.86 - 5.13; p < 0.0001; Tables 3-4). This finding is consistent with numerous studies showing that recontamination at the point of use is a significant source of exposure [16][18][19]. Indeed, studies show that initially potable water can become contaminated during prolonged storage due to improper handling [16]. This observation reinforces the idea that the quality of drinking water depends not only on its source but also on the household practices surrounding its use.

Large household size was also associated with an increased risk of diarrhea in our study, both in bivariate analysis (OR = 2.43; p = 0.001) and after adjustment (aOR = 2.33; p = 0.002; Tables 3-4). This is consistent with observations made in several settings where overcrowding, overburdened sanitation infrastructure, and shared water resources increase the transmission of pathogens [13][14]. However, some studies did not find this association after multivariate adjustment, suggesting that this effect could be mediated by other socioeconomic factors of the household [14].

Safe water management appeared as a significant protective factor in bivariate analysis (OR = 0.54; p = 0.011; Table 3), which is consistent with the findings of several meta-analyses highlighting the importance of hygienic water storage and safe handling practices [14]. After adjustment, this association weakened and no longer reached the conventional significance threshold (aOR = 0.63; p = 0.060; Table 4), suggesting that part of this protective effect is mediated by storage duration, with households practicing safe storage also being those that store water for shorter periods. In contrast to some of the literature that attributes a protective role to improved water sources [14], our study found no significant association between source type and diarrhea, either in bivariate analysis (OR = 1.48; p = 0.144) or after adjustment (aOR = 1.20; p = 0.490; Tables 3-4). This discrepancy suggests that contamination occurs primarily after collection, at the household level, as has already been documented elsewhere [16][19].

The value of point-of-use interventions, particularly solar disinfection (SODIS), is reinforced by our results. Randomized controlled trials have demonstrated its effectiveness in reducing childhood diarrhea [15][20][21], and reviews confirm its potential as a low-cost solution [5][22]. However, some studies report limited or variable effects related to adherence, climatic conditions, and usage practices [11][17]. This heterogeneity underscores the importance of integrating behavioral and contextual dimensions into SODIS implementation strategies in rural areas.

Furthermore, water quality data in the Isiro health zone show that less than 10% of the assessed water points meet drinking water standards [7], which corroborates our findings and confirms the high exposure of rural populations in Haut-Uélé. Studies conducted elsewhere in the DRC and internationally similarly show that microbiological contamination of water sources remains a major problem, even in systems classified as “improved” according to international typology [7][19].

Finally, the contradictions observed in the literature, particularly regarding the effectiveness of household water treatment or the protective role of improved water sources, reflect the multifactorial nature of diarrheal diseases. As Wolf et al. point out, isolated interventions have a limited impact if they are not part of an integrated approach combining water, sanitation, and hygiene (WASH) [14].

2) Limitations of the study:

This study has several limitations that should be highlighted. The collection of diarrhea data based on maternal/guardian recall over two weeks exposes participants to memory and social desirability bias. The cross-sectional design does not allow for establishing a causal link between water management practices and the occurrence of diarrhea. Furthermore, the analysis does not account for the effect of the cluster sampling plan (villages), as the sample size per cluster is insufficient for a stable estimate of within-cluster variance; the reported confidence intervals should therefore be interpreted with reasonable caution [23].

Diarrhea in households remains highly prevalent in the rural health zones of Haut-Uélé, where domestic water management practices, particularly the duration and security of water storage, are major and modifiable determinants, while household size appears to be an additional vulnerability factor. These findings support the promotion of local, low-cost water treatment approaches, such as solar disinfection (SODIS), combined with health education focusing on safe water storage, as complementary measures for diarrhea prevention in rural areas.

Albert Wembakoy Okolongo: conceptualization, methodology, investigation, data curation, formal analysis, and writing of the original draft. Zoé-Arthur Kazadi Malumba: writing, review, and editing. Eugène Basandja Longembe: methodology (epidemiological expertise), validation, and supervision. Joris Losimba Likwela: project administration, coordination, and critical review and editing of the manuscript for important intellectual content. All authors read and approved the final version of the manuscript.