**4. Discussion**

4. Discussion

and no doors.

The water quality assessment in Guinea-Bissau revealed that the water sources used for drinking purposes countrywide were acidic to very acidic, and heavily contaminated with faecal material. Higher levels of contamination were found during the wet season, associated with wells and the use of a bucket to withdraw water. This trend has previously been identified in regional studies performed in the country [12,25].In Guinea-Bissau, the majority of the population retrieve water from shallow (<15 m), hand-dug wells, without any wall isolation or well cover protection. Typically, each well was fitted with a bucket and rope to withdraw water, although some had a manual pump associated. This proportion was visible during the survey, with about one borehole analysed for every six wells. Only 20.5% of the population has access to proper sanitation; thus, communal latrines are the standard, although in rural areas open defecation is still common [9]. Nevertheless, The water quality assessment in Guinea-Bissau revealed that the water sources used for drinking purposes countrywide were acidic to very acidic, and heavily contaminated with faecal material. Higher levels of contamination were found during the wet season, associated with wells and the use of a bucket to withdraw water. This trend has previously been identified in regional studies performed in the country [12,25].In Guinea-Bissau, the majority of the population retrieve water from shallow (<15 m), hand-dug wells, without any wall isolation or well cover protection. Typically, each well was fitted with a bucket and rope to withdraw water, although some had a manual pump associated. This proportion was visible during the survey, with about one borehole analysed for every six wells. Only 20.5% of the population has access to proper sanitation; thus, communal latrines are the standard, although in rural areas open defecation is still common [9]. Nevertheless, most are single pit latrines, with a basic thatched or galvanized corrugated sheet walls and no doors.

most are single pit latrines, with a basic thatched or galvanized corrugated sheet walls The high faecal contamination observed throughout the year is essentially a consequence of the proximity between wells and latrines (<30 m), the presence of freely wandering domestic animals (including cattle), and the contact of the bucket and rope with The high faecal contamination observed throughout the year is essentially a consequence of the proximity between wells and latrines (<30 m), the presence of freely wandering domestic animals (including cattle), and the contact of the bucket and rope with contaminated soil, as reported by several previous studies in Guinea-Bissau [12–14,26] and perceived by the authors in the field.

contaminated soil, as reported by several previous studies in Guinea-Bissau [12–14,26] and perceived by the authors in the field. The influence of pit latrines on groundwater quality was previously described, being recognized as a major source of water contamination depending on the surrounding environment, particularly hydrological and soil conditions [27–29]. Rainfall promotes the mobilization of soil particles through infiltration and percolation that eventually reach the The influence of pit latrines on groundwater quality was previously described, being recognized as a major source of water contamination depending on the surrounding environment, particularly hydrological and soil conditions [27–29]. Rainfall promotes the mobilization of soil particles through infiltration and percolation that eventually reach the subsurface groundwater, conveying associated bacteria and viruses. Sediments are well known reservoirs for microorganisms, typically revealing higher bacterial levels than the water column [30]. Indeed, in accordance with other studies [13,26], high levels of

subsurface groundwater, conveying associated bacteria and viruses. Sediments are well

tamination could be observed in the wet season, associated with a simultaneous increase in turbidity. Turbidity in water is caused by suspended particles or colloidal matter, and

contamination could be observed in the wet season, associated with a simultaneous increase in turbidity. Turbidity in water is caused by suspended particles or colloidal matter, and may be caused by inorganic or organic matter, or a combination of the two [31]. Due to the high superficial area and metabolic substrate concentration, high turbidity can provide an adequate environment for microorganism growth and persistence. Indeed, drinking water turbidity has been associated with the incidence of gastrointestinal diseases [32]. In Guinea-Bissau, the reported diarrhoea episodes systematically peak at the onset of the wet season [33,34], and the main cholera outbreaks have been reported during the wet season [11]. Additionally, the persistent high water temperature (average 29.1 ◦C) observed in wells year-round can also contribute to foster microbial growth [35].

Furthermore, the majority of wells were fitted with buckets and ropes that are often placed on the ground due to the lack of a basic overhead frame to hang them when not in use. This may allow contact with animals and human excreta; moreover, the tools may not exclusively be used to retrieve water. The aggravated situation was confirmed by the results obtained from the models, indicating that the method used to collect water was one of the most influential predictors. The use of a bucket considerably increased the contamination levels. On the other hand, boreholes (>20 m) were drilled mechanically and fitted with a pump (solar, electric), and were thus less prone to contamination.

The relationship between faecal indicators and the nitrogen species strengthen the hypothesis stated above; that microbial contamination enters groundwater due to infiltration and percolation from the surface. The presence of high concentrations of ammonium, nitrate, or nitrite in drinking water are recognized as indicators of possible bacterial, sewage, and animal waste pollution or agricultural runoff [36]. Moreover, there is an increased risk of methemoglobinemia development in bottle-fed infants associated with high concentrations of N species in drinking water, which can further be complicated by the concurrent presence of microbial contamination [36,37]. Additionally, nitrate appears to competitively inhibit iodine uptake, and the long-term exposure by drinking water intake can contribute to the iodine deficiency problem felt in countries such as Guinea-Bissau [36,38].

The faecal contamination was revealed to be related with latitude, with an increment towards the northern part of the country, that can be potentially explained by additional faecal contamination associated with the livestock presence. Although recent data are not available, according to the national livestock census in Guinea-Bissau conducted in 2009, it was estimated that the total number of cattle was approximately 1,325,412, mainly concentrated in the northern areas (Gabu, Bafata, and Oio regions) [39], owned by Fulani, Mandinga, and Balanta ethnic groups. The practice of extensive cattle ranching still dominates in Guinea-Bissau, with a marked transhumance period during the dry season for pasturage and water [40]. Cattle lairage is an unused practice in Guinea-Bissau and livestock roam free in the fields, representing a potential pollution source for unprotected shallow wells. It could be argued that the lairage of cattle could somehow contribute to a diffuse contamination decrease; however, the solution is unworkable due to the lack of water and fodder, technical resources, and infrastructure support.

Overall, similarly to other studies [12–14], the chemical contamination was less relevant, with metal concentrations below the acceptable limits for the majority of the studied water sources. Nonetheless, it is important to note that high metal levels were observed in several wells, and the consumption of elevated levels of metals through drinking water has been associated with the development of health problems, including cancer [31]. Again, the positive correlation found between metal concentration and turbidity indicated the potential role of soil particles as a natural contamination source. During the wet season, the soil particles and associated metal-rich leachates can easily be mobilized by percolation and infiltration, reaching the subsurface groundwater that feeds the shallow wells. In the dry season, the water–soil contact is promoted by the low water level and higher residence time of the water, with increased contact with the earth walls and bottom sediments, fostering high water turbidity.

The majority of the water sources were outside the suitable pH range for drinking water according to EU standards, in the acidic to very acidic interval, a consequence of red, sulphur-rich, sandy-clay soil characteristics [41]. The consumption of acidic water can have a direct impact on population health, particularly in dental erosion [42,43] and through the potential mobilization of heavy metals [44]. Currently, very limited working water networks are available in the country; therefore, the risk of metal contamination through pipes does not seem to be problematic, although such low pH values have to be taken into account in the construction of future infrastructure or rehabilitation initiatives, in order to choose the most suitable materials. Additionally, the corrosion of the materials used in constructing well and distribution systems can enable the feed and growth of microorganisms from adjacent areas in the water used for drinking. Bacteria can adapt to environmental conditions such as low pH, potentially reducing the stomach acidic barrier efficiency, and consequently, the required infectious dose to cause disease [45].

The access to safe drinking water, in addition to being a basic human right, is associated with population health, and consequently, with poverty. Waterborne diseases linked to inadequate WASH are a key public health concern [46–48], particularly in middle- and low-income countries, which needs to be addressed for country development. Furthermore, the expected population growth and the climate change scenario will pose an additional threat to WASH infrastructure and services [49].

This study highlighted the urgent need to improve the access to safe drinking water in sub-Saharan countries, such as Guinea-Bissau. For a long-term solution, a robust, countrywide intervention on WASH infrastructure is pivotal. New construction or rehabilitation of the limited water and sanitation networks should be performed, taking into account the local and regional conditions (such as the acidic groundwater), and forearm periodic maintenance and water quality monitoring, which are presently inexistent. To ensure water quality safety, government administration and non-governmental organizations must favour the construction of deep boreholes, even if it means cooperation and co-ordination between agencies, as well as constructing less infrastructure, due to the higher associated costs. Water quality should be regularly monitored, and if needed, promptly treated using the disinfection treatments techniques currently available and applied in countries with limited resources [50,51]. Emphasis should also be placed on the collection and treatment of effluent from latrines, including the construction of sealed tanks—septic tanks—and the disposal of waste into small collective treatment plants with biological beds. Furthermore, scientific and technical advice, prior and during construction, is essential for correct guidance on the establishment of local infrastructure and maintenance.

The traditional or settled way of living can be a hindrance to development; therefore, the implementation of behaviour change programs, with structured formative and educational interventions to raise awareness at the different societal levels (individual, household, community, and institutional) will be decisive to prevent disease transmission. The integration of local stakeholders and the community, throughout the implementation programs, will help to ensure the sustainable use and management of water.

On other hand, considering the urgency overt in the results of this study, the authors propose the short-term implementation of simple, sustainable measures, which could drastically improve the access to safe drinking water, mitigating the associated health risk:

