The quality of drinking and domestic water from the surface water sources (lakes, rivers, irrigation canals and ponds) and springs in cholera prone communities of Uganda: an analysis of vital physicochemical parameters

Water is the most abundant resource on the planet earth [1], however its scarcity affects more than 40% of the people around the world [2]. Natural water is an important material for the life of both animals and plants on the earth [3]. Consequently, access to safe drinking water is essential for health and a basic human right that is integral to the United Nations Resolution 64/292 of 2010 [4]. The United Nations set 2030 as the timeline for all countries and people to have universal access to safe drinking water; this is a Sustainable Development Goal (SDG) 6 of the 17 SDGs [5]. The availability of and access to safe water is more important to existence in Africa than it is elsewhere in the world [6]. Least Developed Countries (LDCs) especially in sub-Saharan Africa have the lowest access to safe drinking water [7]. In Africa, rural residents have far less access to safe drinking water and sanitation than their urban counterparts [8].

Natural water exists in three forms namely; ground water, rain water and surface water. Of the three forms, surface water is the most accessible. Worldwide, 144 million people depend on surface water for their survival [9]. In Uganda, 7% of the population depends on surface water (lakes, rivers, irrigation canal, ponds) for drinking water [10]. The same surface water is a natural habitat for many living organisms [11] some of which are responsible for transmission of infectious diseases such as cholera, typhoid, dysentery, guinea worm among others [12]. Surface water sources include lakes, rivers, streams, canals, and ponds. These surface water sources are often vulnerable to contamination by human, animal activities and weather (storms or heavy rain) [13, 14]. Globally, waterborne diseases such as diarrheal are responsible for more than two million deaths annually. The majority of these deaths occur among children under-5 years of age [15].

Cholera, a waterborne disease causes many deaths each year in Africa, Asia and Latin America [16]. In 2018 alone, a total of 120,652 cholera cases and 2436 deaths were reported from 17 African countries to World Health Organization [17]. Cholera is a major cause of morbidity and mortality in Uganda [18]. The fishing communities located along the major lakes and the rivers in the African Great Lakes basin of Uganda constitutes 5% of the Uganda’s population, however these communities were responsible for the majority (58%) of the reported cholera cases during the period 2011–2015 [19]. Cholera outbreaks affect predominantly communities using the surface water and the springs. There is also high risk of waterborne disease outbreaks in the communities using these types of water [20, 21]. Studies of the surface water from water sources located in the lake basins of the five African Great Lakes in Uganda identified Vibrio. cholerae [22, 23] though no study isolated the toxigenic V. cholerae O1 or O139 that cause epidemic cholera. Cholera outbreaks in the African Great Lakes basins in Uganda have been shown to be propagated through water contaminated with sewage [20, 24]. Cholera is one of the diseases targeted for elimination globally by the WHO by 2030 [25]. Hence, to prevent and control cholera outbreaks in these communities, promotion of use of safe water (both quantity and quality), improved sanitation and hygiene are the interventions prioritized by the Uganda Ministry of Health [26]. Most importantly, provision of adequate safe water is a major pillar of an effective cholera prevention program given that water is the main mode of V. cholerae transmission [27, 28].

Availability of adequate safe water is essential for prevention of enteric diseases including cholera [29]. Therefore, access to safe drinking and domestic water in terms of quantity and quality is key to cholera prevention. Water quality is defined in terms of three key quality parameters namely, physical, chemical and microbiological characteristics [30]. A less common but important parameter is the radiological characteristics [31]. In regards to the physicochemical parameters, there are five parameters that are essential and impacts life (both flora and or fauna) within the aquatic systems [32]. These vital physicochemical parameters include pH, temperature, dissolved oxygen, conductivity and turbidity [32].

pH is a value that is based on logarithm scale of 0–14 [33]. Aquatic organisms prefer pH range of 6.5–8.5 [34‐36]. Low pH can cause the release of toxic elements or compounds into the water [37]. The optimal pH for V. cholerae survival is in basic range (above 7). Vibrio cholerae may not survive for long in acidic pH [38]. A solution of pH below 4.5 will kill V.cholerae bacteria [39].

Most aquatic organisms are adapted to live in a narrow temperature range and they die when the temperature is too low or too high [34]. Vibrio cholerae, bacteria proliferate during algae bloom resulting in cholera outbreaks [40, 41]. This proliferation could be due favourable warm temperature [42]. Relatedly, V. cholerae isolation from natural water in endemic settings is strongly correlated with water temperature above 17 °C [43].

Dissolved oxygen is the oxygen present in water that is available to aquatic organisms [34]. Dissolved oxygen is measured in parts per million (ppm) or milligrams per litre (mg/L) [35]. Organisms in water need oxygen in order to survive [44]. Decomposition of organic materials and sewage are major causes of low dissolved oxygen in water [12].

Water conductivity is the ability of water to pass an electrical current and is expressed as millisiemens per metre (1 mS m-¹ = 10 μS cm^− 1) [29]. Most aquatic organisms can only tolerate a specific conductivity range [45]. Water conductivity increases with raising temperature [46]. There is no set standard for water conductivity [45]. Freshwater sources have conductivity of 100 – 2000μS cm^− 1. High water conductivity may be due to inorganic dissolved solids [46].

Turbidity is an optical determination of water clarity [47]. Turbidity can come from suspended sediment such as silt or clay [48]. High levels of total suspended solids will increase water temperatures and decrease dissolved oxygen (DO) levels [12]. In addition, some pathogens like V. cholerae, Giardia lambdia and Cryptosporidia exploit the high water turbidity to hide from the effect of water treatment agents and cause waterborne diseases [49]. Consequently, high water turbidity can promotes the development of harmful algal blooms [41, 50].

Given the importance of the water physicochemical parameters, in order to ensure that they are within the acceptable limits, the WHO recommends that they are monitored regularly [51]. The recommended physicochemical parameters range for raw water are for pH of 6.5–8.5, turbidity of less than 5Nephlometric Units (NTU) and dissolved oxygen of not less than 5 mg/L [51]. Surface and spring water with turbidity that exceeds 5NTU should be treated to remove suspended matter before disinfection by either sedimentation (coagulation and flocculation) and or filtration [52].

Water chlorination using chlorine tablets or other chlorine releasing reagent is one of the most common methods employed to disinfect drinking water [53, 54]. Chlorination is an important component of cholera prevention and control program [55]. In addition to disinfection to kill the pathogens, drinking water should also be safe in terms of physicochemical parameters as recommended by WHO [51]. However, to effectively make the water safe using chlorine tablets and other reagents, knowledge of the physicochemical properties of the surface and spring water being disinfected is important as several of the parameters affect the active component in the chlorine tablets [56]. For example, chlorine is not effective for water with pH above 8.5 or turbidity of above 5NTU [53].

Generally, there is scarcity of information about the quality and safety of drinking water in Africa [57]. Similarly, few studies exist on the physicochemical characteristics of the drinking water and water in general in Uganda. Furthermore, information from such studies is inadequate for use to increase safe water in cholera prone districts of Uganda where the need is greatest. The cholera endemic communities of Uganda [19, 21, 24] have adequate quantities of water that is often collected from the Great lakes, rivers and other surface water sources located within the lake basins. However, the water is of poor quality in terms of physicochemical and microbiological characteristics. Several studies conducted in Uganda have documented microbiological contamination of drinking water [20, 24, 58, 59]. However, few studies exist on the physicochemical characteristics of these water. Furthermore, these studies focused on few water sources, for example testing the lakes and omitted the rivers, springs and ponds or testing the rivers and omitted the other water types. One such study was carried out on the water from the three lakes in western Rift valley and Lake Victoria in Uganda [23], This study did not assess the other common water sources such as the rivers, ponds and springs that were used by the communities for drinking and other household purposes. Other studies on water physicochemical characteristics assessed heavy metal water pollution of River Rwizi (Mbarara district, Western Uganda) [60] and of the drinking water (bottled, ground and tap water) in Kampala City (Central Uganda) [61] and Bushenyi district (Western Uganda) [62]. These studies found high heavy metal water pollution in the drinking water tested. The information gathered from such studies is useful in specific study area and is inadequate to address the lack of safe water in the cholera endemic districts of Uganda where the need for safe drinking water is greatest. Several epidemiological studies in Uganda have attributed cholera outbreaks to use of contaminated surface water [20, 21, 24, 63]. Furthermore, studies conducted on the surface water focus on pathogen identification [63, 64] leaving out the water physicochemical parameters which are equally important in the provision of safe drinking water [53] and are necessary for survival of all living organisms (both animals and plants) [44].

Therefore, the aim of this study was to determine the physicochemical characteristics of the surface water sources and springs located in African Great Lakes basins in Uganda so as to guide the interventions for provision of safe water to cholera prone populations [19‐21, 24, 58] of Uganda. This study in addition has the potential to guide Uganda to attain the United Nations SDG 6 target of universal access to safe drinking water [2] and the WHO cholera elimination Roadmap [25] by 2030. Furthermore, these findings may guide future studies including those on causal-effect relationship between physicochemical parameters and infectious agents (pathogens).

This was a longitudinal study that was conducted between February 2015 and January 2016 in six districts of Uganda that are located in the African Great Lakes basins of the five lakes (Victoria, Albert, Kyoga, Edward and George). These districts had ongoing cholera outbreaks or history of cholera outbreaks in the previous five to 10 years (2005–2015). In addition, the selected study districts had border access to the following major water bodies (lakes: Victoria, Albert, Edward, George and Kyoga). The study area was purposively selected because the communities residing along these major lakes contributed most (58%) of the reported cholera cases and deaths in Uganda [19, 65] and in the sub-Saharan Africa region [66] in the past 10 years. Water samples were collected monthly from 27 sites used by the communities for household purposes that included drinking. Water samples were then tested to determine the vital physicochemical parameters. The water samples were collected from lakes, rivers, springs, ponds and an irrigation canal that were located in the lake basins of the five African Great Lakes in Uganda. In one site, water was also collected from a nearby drainage channel and tested for V. cholerae [22] and physicochemical parameters. However, because the channel was not used for drinking the results were omitted in this article. Water samples were analysed to determine the pH, temperature, dissolve oxygen, conductivity and turbidity. The study sites were located in the districts of Kampala and Kayunga in central region of Uganda; Kasese and Buliisa districts in western Uganda; Nebbi and Busia districts in northern and eastern Uganda respectively. The study sites were the same as for the simultaneous bacteriological V. cholerae detection study [22] and are shown in Fig. 1.

A total of 318 water samples were tested from 27 sites as follows; lake water 40.9%, (130/318), rivers water 26.4% (84/318), ponds water 17.9% (57/318), spring water 11.0% (35/318) and canal water 3.8% (12/318).

This study showed that water for drinking and domestic purposes from the surface water sources and springs in cholera affected communities/districts of Uganda were not safe for human use in natural form. The water samples from the water sources in the study area did not meet the WHO drinking water quality standards in terms of the important physicochemical parameters. In addition, all the surface water sources and the springs tested had turbidity above the WHO recommended level of 5NTU yet the same water were used for domestic purposes including drinking in the natural form by the households. The study also found variations in the other physicochemical parameters (pH, temperature, dissolved oxygen and conductivity) between study sites on the same lake and between the different water sources.

While the majority of the water sources had mean water physicochemical characteristics (excluding turbidity) in acceptable range, few water sources, mainly the sites on Lake George, including the springs and ponds had pH and dissolved oxygen outside the recommended WHO ranges. These water sources that did not meet the WHO drinking water standards could expose the users to harmful effects of unsafe drinking water including waterborne diseases such as cholera. The present study findings of high water turbidity if due to algae bloom could encourage pathogen persistence and infection spread, including V. cholerae bacteria [40, 41] resulting in ill-health and cholera epidemics. In addition, the high water turbidity complicates water disinfection as it gives rise to significant chlorine demand [53]. The increased chlorine demand can be costly and difficult to ensure constant availability for disinfection of water since Uganda and several other developing countries need and receive supplementary donor support [69].

In regard to temperature, dissolved oxygen and conductivity, the majority of the surface water sources and springs tested met the recommended WHO drinking water standards. However, a few water sources such as River Lubigi in Kampala district had mean dissolved oxygen below the recommended WHO drinking water standards. Therefore, in order to ensure universal access to safe drinking water, the water sources that had vital physicochemical parameters outside the WHO drinking water range could be targeted for further studies.

There were statistically significant differences in the water physicochemical characteristics between the different sites and sources (lakes, rivers, springs and ponds). Despite these differences, the required approaches to ensure safe water access to the communities may not differ across sites. First and foremost, all sites and water types will need measures that reduce the high water turbidity to WHO acceptable levels. Secondly, in few instances, such as the water sources with pH in acidic range (Katanga spring in Kampala district, Lake Victoria Basin and Wanseko pond in Buliisa district, lake Albert basin) in addition to requiring further studies to identify the causes of the low pH (acidity), such water sources may also require the use of water treatment methods that neutralize the excess acidity [54]. Furthermore, since acidity is usually associated with increased solubility of toxic heavy metals (lead, arsenic and others) [34], testing such water for metallic contamination may be required. Heavy metal contamination of water causes ill-health due to chronic exposure which is cumulative and manifest late for correction to be done [70].

The findings of this study also highlight the differences in water quality between the urban surface water sources and springs (Kampala district) and the rural surface sources and springs (other study districts – Kasese, Kayunga, Busia, Nebbi and Buliisa) The water sources that met the WHO recommended drinking water quality standards [53] were mostly the rural springs and the rivers. However, these differences between the rural and the urban water sources do not alter the required approaches to ensure access to safe water which is by promoting measures that reduce the high water turbidity in combination with water disinfection to remove the pathogens. The relatively good quality of rural water sources compared to the urban ones could have been due to availability of plenty of vegetation in rural setting that filtered the water along the way downstream and possibly low level of pollution from industrial inputs in rural areas than in urban areas [71, 72].

In relation to cholera outbreaks in the study communities, naturally, the physicochemical conditions for survival of V. cholerae O1 occur in an estuarine environment and other brackish waters [73, 74]. In such circumstances, the favourable physicochemical conditions for V. cholerae isolation are the high water turbidity [49] and temperature of above 17 °C [43]. Interestingly, all the surface water sources and the springs tested had favourable physicochemical characteristics for the survival of V. cholerae in terms of these two parameters (high water turbidity and temperature of above 17 °C). Furthermore, two lakes sites (Kahendero FLS and Hamukungu FLS, Lake George, Kasese district) had also favourable mean pH for the survival of V. cholerae of 9.03 ± 0.17 and 9.13 ± 0.23 respectively. Favourable pH for V. cholerae survival in waters of Lake George was previously documented in the same area [23]. Hence, the frequent cholera outbreaks [19‐21, 24] in the study area could be attributed to both the favourable physicochemical water characteristics and use of unsafe water.

There were wide variations in conductivity between water sources and within the same source overtime. High water conductivities were recorded in the months of January to March 2015 (dry season), possibly due to high evaporation which increased the concentration of electrolytes present in water. Likewise, two rivers namely. River Lubigi (Kampala district) and Nyamugasani (Kasese district) had higher mean conductivities of 460.51 ± 57.83 μS/cm and 946.08 ± 3.63 μS/cm respectively than for typically unpolluted river of 350 μS/cm [75]. Consequently, given that the two rivers flow through areas of heavy metal mining (copper and cobalt mines in Kasese district by Kilembe Mines Limited and Kasese Cobalt Company Limited) and industrial activities (Kampala City), it is possible for the high water conductivity to be due to the heavy metal contamination as previously documented in drinking water in South-western Uganda [62] and Kampala City [61]. Thus, specific studies are required on water from the two rivers to determine the true cause of the high conductivity and to guide mitigation measures.

Hence, more efforts are required to promote safe water access in Uganda to attain the WHO cholera elimination target [25] and SDG 6 by 2030 since 26% (36/135) of mean physicochemical water tests did not meet WHO drinking water quality standards [53]. These findings together with those of the previous studies which demonstrated the presence of pathogenic V. cholerae in the same water sources [22, 23, 76] should guide stakeholders to improve access to safe water in the Great Lakes basins of Uganda holistically. Thus, measures such as promotion of use of safe water (using water disinfection), health education, sanitation improvement and hygiene promotion that address both the water bacteriological contents and physicochemical parameters should be considered in both the short and medium terms. However, long term plan to increase access to safe water by construction of permanent safe water treatment plants and distribution systems (pipes) should remain a top priority.

In the short and intermediate period, focusing on the measures that reduce water turbidity and disinfection of water (to kill microorganisms) should be prioritized so as to facilitate progress towards attainment of SDGs and cholera elimination in the study area. The basis for such prioritization lies in the fact that high water turbidity raises water temperature and prevents the disinfection effects of chlorine on water. These in return promote survival of the microorganisms and consequently cholera and other waterborne disease outbreaks. Furthermore, though boiling of water is feasible and recommended through technical guidelines [26] since it addresses both turbidity and kills the micro-organisms, it has issues of poor compliance due to lack of firewood which is the main cooking energy source in these communities [70]. Therefore, alternative safe water provision targeting reduction of high water turbidity and removal of microorganism by special filters such as decanting and sand filters and flocculation agents which do not need heat energy should be promoted [77, 78]. Also, there is a need to explore the use of solar energy (solar water purifiers) [79] in these communities given their location in the tropics where sunshine is plenty. In the minority of situations, in addition to use of above methods to make water safe, there may be a need to employ different approaches of water purification depending on the water source. For example the water sources with lower or higher than recommended pH [53] (Wanseko pond, Hamukungu and Kahendero FLS on L. George), use of water treatment reagents that are affected by pH such as chlorine tablets should be reevaluated.

In additional to disinfection and turbidity corrective measures for all the water that were studied, each of the springs in the study area (Katanga in Kampala district and Nyakirango and Kibenge springs in Kasese district) will also need a sanitary survey (a comprehensive inspection of the entire water delivery system from the source to the mouth so as to identify potential problems and changes in the quality of drinking water) [80]. The findings of the sanitary survey should then guide the medium and long term interventions for water quality improvement in areas served by targeted springs. The following are some of the interventions that could be carried out after a sanitary survey: provision of a screen to prevent the entrance of animals, erecting a warning signs, digging of a diversion ditch located at the uphill end to keep rainwater from flowing over the spring area, establishment of an impervious barrier (a clay or a plastic liner) to prevent potential contaminants from entering into the water or and others measures described in the handbook for spring protection [81].

Furthermore, as a stopgap measure while access to safe water is scaled up, the communities in the study area should be protected from cholera using Oral Cholera Vaccines [82]. Protection of these communities is necessary since this study shows that favorable conditions for cholera propagation/transmission are present in the water in the study area. The favorable conditions that were documented in this study included the high water turbidity which makes it difficult to disinfect water [53] and the water temperature of above 17 °C which speeds up the multiplication of pathogens [43].

In addition, there were some other important study findings that were not fully understood. For example, some water sources (Kibenge spring and pond (located in Kasese district, western Uganda) had extreme vital physicochemical values for both conductivity and water temperature relative to the rest of above 40 °C and 3000 μS/cm respectively. It is possible that the extreme values were due to geochemical effects documented in water sources around Mount Rwenzori [83]. However, since there was copper and cobalt mining in Kasese district, high water conductivity could have been due to chemical contamination. Similarly, River Lubigi, Kampala district (central Uganda) had very low dissolved oxygen of less than 1 mg/L during some months (for example in January 2015, dissolved oxygen of 0.45 mg/L) which could have been due to organic pollutants from the communities in Kampala City [84] that used up the oxygen in the water. Also, Wanseko pond (Lake Albert basin, Buliisa district) had low pH of 4.84 in February 2015. Such water with low pH have the potential to increase the solubility of heavy metals some of which make water harmful when consumed [85]. Therefore, further studies will be required to better understand such extreme values.

The study showed that surface and spring water for drinking and other domestic purposes in cholera prone communities in Great Lakes basins of Uganda were unsafe in terms of vital physicochemical water characteristics. These water sources had favourable physicochemical characteristics for transmission/propagation of waterborne diseases, including cholera. All test sites (100%, 27/27) had temperature above 17 °C that is suitable for V. cholerae survival and transmission and higher than the WHO recommended mean water turbidity of 5NTU. In addition, more than a quarter (27%) of lake sites and 40% of the ponds had pH and dissolved oxygen outside the WHO recommended range of 6.5–8.5 and less than 5 mg/L respectively. These findings complement bacteriological findings that were previously reported in the study area which found that use of this water increased their vulnerability to cholera outbreaks [22]. Therefore, in order for Uganda to attain the WHO cholera elimination and the United Nations SDG 6 target by 2030, stakeholders (the Ministry of Water and Environment, the local governments, Ministry of Health development partners and others) should embrace interventions that holistically improve water quality through addressing both physicochemical and biological characteristics. Furthermore, studies should be conducted to generate more information on the other physicochemical parameters not included in this study such as detection of the heavy metal contamination.