Surface water pollution refers to the contamination of rivers, lakes, and oceans by harmful substances, often due to human activities and certain natural disasters [1] [2] . It can have serious consequences on aquatic ecosystems leading to the death of species that inhabit them, changes in color, and/or the nature of the water, etc., biodiversity, and human health [3] . Water quality is a critical parameter that greatly affects human health and aquatic life [4] . Indeed, proper water management to ensure rural development remains a challenge, as according to the latest estimates from the United Nations, 2 billion people still had no access to drinking water at home in 2020, and about 771 million people had to travel at least 30 minutes from their homes to access drinking water, with over a hundred million people worldwide drinking untreated water of poor quality [5] . This water pollution is a fundamental issue for developing countries where the population boom is high and where governments have divergent investment priorities [6] . In these countries, 90% to 95% of all wastewater and 75% of all industrial waste, on average, are discharged into surface waters without prior treatment [1] [7] .

In Guinea, more precisely in the urban community of Kankan, a significant amount of toxic waste is generally discharged, caused by erosion into the Milo River, ordinary wells, and stagnates around the boreholes. During the winter period, the area being agricultural in nature, the waters, infected by various chemicals, are discharged daily. To successfully carry out this study, field visits, interviews with resource persons, and photography were conducted to identify the different sites for water sampling to analyze quality. This interview also made it possible to understand the different uses the population makes of the waters of the Milo River, namely: watering vegetable crops, fishing, washing vehicles and clothes, the body, etc., exposing them to a health risk because today, along this river has become a dumping ground for all sorts of waste and the abusive use of pesticides and fertilizers, it has become an uncontrolled landfill. Despite this advanced level of pollution, it is also used as a source of drinking water by SEG (Société des Eaux de Guinée).

As a contribution to the efforts of monitoring and protecting against water pollution, we have chosen the present study: in the urban commune of Kankan (Republic of Guinea) in 2024.

The goal of this work is to evaluate the quality of these waters for sustainable and risk-free use.

Table 2 and Table 3 with Figure 4 presented the physical and chemical result for well water.

It emerges from Table 3 and Table 4 that certain physico-chemical parameters do not meet the standards defined by the WHO [11] . Some pH values are very low compared to the average [12] , while those for electrical conductivity are quite high. The concentrations of nitrite and phosphate ions are well above normal [13] . The levels of calcium (3.2 - 42.3 mg/L) and bicarbonates (9.76 - 185.44 mg/L) indicate respectively that this water ranges from soft to moderately hard and that the mineralization is variable. The calcium hardness (mg/L) of the wells in CMIS, Sénkéfara, and Energie is very low, indicating that this water is soft; however, that of the wells in Kabada, Dibida, and Sogbè is high, indicating that this water is very hard [14] . These results show that these well waters are unfit for consumption without prior treatment.

The concentrations of calcium ions (3.2 - 42.33 mg/L) in the CMIS well are low, which could indicate soft water; however, in the Dibida well sample, they are high, which means this water is hard. The concentrations of bicarbonate ions (9.76 - 185.44 mg/L) are very high in these samples, indicating the softness of these waters but also a significant presence of dissolved minerals ( Table 3 ). The concentrations of calcium carbonate are high for the Kabada and Dibida wells, which indicates that these waters are hard compared to other samples where these values are acceptable (soft waters).

The concentrations of iron, aluminum, copper, lead, and zinc ions presented in Figure 5 are within the acceptable limits according to the WHO standard [15] . This suggests an absence of significant contamination, thus these waters do not present a health risk [16] . Generally speaking, it can be said that the hardness of these samples is variable but leans much more towards hard water. The concentrations of zinc ions are above the recommended standard and may promote corrosion of plumbing. However, the other metals are compliant. Some samples show CaCO₃ values above 100 mg/L confirming that these waters are hard. In light of all these observations, it can be concluded that these analyzed waters do not comply with drinking water standards and are therefore unfit for human consumption [17] .

The results of the metal concentrations presented in Table 4 show that the concentrations of Iron (0.5 mg/L), Aluminum (<0.2 mg/L), Copper (<2 mg/L), and Lead (<0.01 mg/L) comply with the standards set by the WHO [18] . However, the Zinc concentration (3.41 - 4.42 mg/L) is very high compared to the WHO standard [19] . These results indicate that the water is generally soft and not polluted by these metals, but the high Zinc content in these samples may cause corrosion of water pipes [20] .

The conductivity values are very low ( Figure 6 ). They indicate that this water is very poorly mineralized, which can have consequences if regularly consumed, as it contains very few essential mineral salts such as calcium, magnesium, and potassium. Water that is very poorly mineralized may tend to absorb minerals from the body (notably in the teeth and bones) that facilitate water absorption in the intestine, so it is not recommended for hydration [21] . The turbidity is generally acceptable, but the value of 3.2 NTU at the Dibida site indicates the presence of suspended matter, which may carry an increased microbial risk if not disinfected ( Table 5 ).

The values of dissolved oxygen found are acceptable but slightly low compared to WHO standards [5] . This low variation may indicate water stagnation, meaning it is slightly in motion and thus promoting algae growth, poor oxygen distribution, and the accumulation of sediments or pollutants [4] . In light of WHO standards (0.01 mg/L), the nitrite values (0.9, 1.71, and 2.2 mg/L) are very high [13] . This high rate of nitrite ions may be due to uncontrolled urbanization; it can pose health problems for those who use this water. This harmful effect is particularly visible in infants (methemoglobinemia) and local population in this urban District (typhoid fever, gastrointestinal disorders such as diarrhea). This result indicates that the waters from the Kabada 2, Dibida, and Energie sites require treatment or disinfection before any consumption.

Ammonium ion levels (0.23 mg/L) are acceptable according to WHO standards (0.5 mg/L) [16] , but when combined with nitrite levels, it can indicate an active degradation of water quality. This accumulation (ammonium-nitrite) can come from organic matter, fertilizers, pesticides, animal urine, etc. [22] . The pH value and levels of nitrate, chloride, sodium, and sulfate ions are very good as they fall within the WHO range [11] [16] . For phosphate ions, the levels are high ( Table 6 ). Drinking water should not contain so many phosphates. This level can pose risks of eutrophication in natural environments [13] .

The concentrations of magnesium ions and free chlorine are low. This low magnesium ion content indicates that these waters may bind magnesium from the body for its absorption, which can lead to a deficiency of this element in the organism [23] . Regarding free chlorine, its low value presents a risk of attack for the organism. It should not be totally absent in water; otherwise, we expose ourselves to microbiological risks as the turbidity of the water may increase. Considering the temperature values (24.5˚C to 25.6˚C), we can say that these waters are warm. This increase in temperature can encourage microbial proliferation in these waters, and therefore it must be disinfected before any use.

The pH of the groundwater from CMIS and Sénkéfara is below the standard [5] [11] , indicating slightly acidic water. This can lead to corrosion of the pipes and affect the taste of the water. The measured conductivity values are very low compared to the standard [24] , suggesting poorly mineralized water with low dissolved salts or dilution by rainwater [25] . Regarding turbidity, values ranging from (0.19 to 1.69 NTU) are below (5 NTU), which is the WHO standard indicating clear water. However, the highest values could signal the presence of suspended particles. These physical results are summarized in ( Table 7 ) and ( Figure 7(a) ).

The levels of dissolved oxygen are appreciable except in the case of the UJNK drilling. Low levels of dissolved oxygen may indicate organic pollution or stagnation of water, which is detrimental to aquatic life [19] . Table 8 and Figure 7(b) present the chemical result for groundwater. Nitrate ion concentrations are above the standard [13] in the samples from the UJNK, Dibida market, Sogbé, and Sénkéfara drilling waters, suggesting contamination from agricultural or domestic sources. For nitrite ions, only the sample from the UJNK drilling with a concentration of (0.37 mg/L) exceeds the WHO standard of (0.20 mg/L), indicating recent organic pollution.

Ammonium ions have levels all below the standard [16] , which is favorable for health, but a high level of ammonium ion may indicate organic pollution. The absence of phosphate ions in the samples was noted, which indicates a favorable result for health, as their presence can promote the proliferation of algae [26] . Sulfate ions have values well below the WHO standard [7] , indicating an absence of sulfate pollution. The levels of magnesium ions compared to the WHO standard (10 - 50 mg/L) are very low in most samples, suggesting fresh water.

The chloride and sodium ion levels are practically compliant with WHO standards [27] , but the highest chloride ion value approaching the limit of 250 mg/L for the water from the CMIS Borehole may affect the taste of the water, while the high sodium ion level for this same Borehole may have complications for people on a low-sodium diet [28] . Most of the samples from the Borehole waters (UJNK, Marché Sogbè, and Sénkéfara) show an absence of residual chlorine, which may indicate a lack of disinfection. All temperatures are typical of surface water in tropical areas.

It follows from these results that the high levels of nitrates, nitrites, and low dissolved oxygen content lead to organic pollution of these waters which could be caused by agricultural or domestic discharges. The slightly acidic pH and low mineralization can lead to corrosion of distribution infrastructures. The absence of free chlorine in most samples indicates a lack of disinfection, increasing the microbiological risk [29] . It is necessary to implement treatment systems to reduce nitrates, nitrites, and also adjust the pH to ensure adequate disinfection of water while maintaining appropriate levels of residual chlorine. Regular analyses should then be carried out to monitor water quality and detect any variations. Finally, local authorities should implement measures to protect water sources from contamination, in particular by controlling agricultural and domestic discharges.

This study presents the results of physico-chemical analysis of six water samples from different sources: ordinary wells, boreholes, taps, and the Milo River ( Figure 8 ). The analyzed samples contain calcium (Ca), iron (Fe), aluminum (Al), zinc (Zn), copper (Cu), and lead (Pb) ions, and the concentrations of these elements are compared to the drinking water quality standards established by the WHO. The results indicate that the calcium (Ca) levels are low, indicating soft water. These values do not present any health risks, but the water is low in minerals, thus the calcium level needs to be improved. The iron (Fe) and zinc levels are above the WHO recommendation [15] .

A high iron content can lead to a possible metallic taste, stains on laundry or fixtures that may be due to corrosion of the piping, iron-rich soils, and high oxidation possibilities, while a high zinc content can affect taste without posing a health risk. This presence of zinc can come from the corrosion of galvanized pipes or industrial waste. For aluminum (Al) and copper (Cu), the levels are at the maximum recommended limit by the WHO, requiring monitoring. This result does not have a significant direct impact on health, but the accumulation of these elements is harmful. The presence of aluminum could come from the galvanization of aluminum objects, while that of copper would come from the oxidation of piping. Lead (Pb) is detected at <0.05 mg/L, a value above the detection threshold set by the WHO standard (0.01 mg/L) [15] , therefore a potential risk cannot be excluded ( Table 9 ).

It follows from these results that this water, before domestic use, must undergo treatment through aeration/filtration (activated carbon, ceramic) to eliminate harmful metals and regularly monitor the levels of these metals because their increase will be very detrimental to health.

The results in Table 10 and Figure 9 show that pH values between 7.05 and 7.10 correspond to neutral water, while a pH value of 7.74 indicates that the water is slightly basic. The conductivity values indicate low mineralization, meaning a lack of calcium, phosphate, and magnesium, which can lead to digestive disorders, malabsorption (celiac disease, Crohn’s disease), renal or hepatic insufficiency, and hormonal disorders (dysfunction of parathyroid hormone (PTH)), thyroid or sexual hormones in populations that consume it [23] .

This low mineralization can still cause diseases in children such as rickets (bone deformity, growth retardation, pain) and problems of osteomalacia (diffuse bone pain, fatigue, muscle weakness); long-term osteoporosis (bone fragility, increased fracture risk, dental problems, cramps, muscle spasms related to electrolyte imbalances, neurological disorders in adults [23] . The COD (chemical oxygen demand) values obtained are below the limit value of 10 mg/L but accepted by the WHO [19] . COD is the consumption of oxygen by powerful chemical oxidants to oxidize the organic and mineral substances in water. It is one of the most commonly used methods to assess the overall load of organic pollutants in water. This low level of dissolved oxygen indicates that the water is probably eutrophic or stagnant in some cases, suggesting a likely decrease in biodiversity. It is worth noting that temperature and dissolved oxygen are negatively correlated. This means that the higher the temperature, the less oxygen is available.

The turbidity value of 15.53 NTU shows that the water under the Milo bridge is less turbid, while values of 22.88 NTU and 33.9 NTU indicate that the water from Milo pumping station and Milo slaughterhouse is quite cloudy, which suggests the likely presence of suspended matter and thus organic or specific pollution. The TSS refers to solid, insoluble materials that are visible to the naked eye and are present in suspension in water. This includes clays, sands, silts, plankton, and other aquatic microorganisms. The quantity of TSS varies according to the season and the water flow regime; they result from soil erosion and leaching during rainy weather, especially when precipitation is intense and in flood situations.

Biodegradable TSS significantly contributes to the oxygen demand and leads to a decrease in the concentration of dissolved oxygen in the aquatic environment. These materials affect water transparency and reduce light penetration, thereby affecting photosynthesis [17] .

Value peaks are observed during the rainy season in the Stations and are likely a result of the presence of discharges around the wells. These discharges are formed by the natural fermentation of leachate. This turbid water would explain the low dissolved oxygen levels observed ( Table 10 ). Phosphorus in the natural environment is found in the form of phosphates (calcium, iron, and aluminum) in volcanic and sedimentary rocks. Its transfer into water occurs through soil and rock erosion. Plants absorb the solubilized phosphates for photosynthesis [30] . It is transferred along the food chain through the consumption of plants by animals. Phosphorus is again solubilized through the decomposition of dead matter by microorganisms [31] .

Nitrate ions are present in very low concentrations and completely absent in some places, while nitrite ions are absent in all samples, which is favorable for water quality. The concentrations of ammonium and phosphate ions are very high compared to the WHO standard [11] , indicating respectively a slight nitrogen pollution in some cases (feces, organic decomposition) and risks of eutrophication in the case of Milo Pumping Station and Milo slaughter. The value of ion sulfate (17.92 mg/L) indicates the presence of mineral or industrial pollution at the site of the river Milo under bridge ( Table 11 ).

The combined results of this study show that surface water (Milo water, ordinary wells) is the most polluted because it is exposed to human activities, compared to groundwater (boreholes and taps) which is less polluted.

This present study aims to evaluate the quality of water from: boreholes, ordinary wells, taps, and the Milo River in the urban municipality of Kankan. To do this, in July 2024, a sample collection campaign was conducted at nine sites in the locality during the rainy season. The results for parameters such as temperature, pH (5.10 - 5.75), electrical conductivity (464 - 703 µs), turbidity (15.53 - 22.88 NTU), and dissolved oxygen (DO) in the waters of ordinary wells, boreholes, and the Milo River do not comply with WHO standards, thus these waters require prior treatment before use. The analysis of ions such as nitrites (0.02 - 2.20 mg/L) for ordinary wells, boreholes, and taps; phosphate ions (11 - 20 mg/L) and zinc (3.71 - 4.42 mg/L) for ordinary wells, Drillings and Milo river; iron ions (0.5 mg/L) for the Milo river; ammonium ions (0.26 - 0.6 mg/L) for standard drillings and wells; lead (0.05 mg/L) and nitrate ions (56 - 129 mg/L) for the drillings were measured using the colorimetric method. These results also indicate that most of these waters are polluted due to their content of these various ions. The statistical analysis of the data for certain chemical parameters (concentration of nitrite and phosphate ions) was conducted using Stata 15 software, and the correlation test between the parameters yielded very significant values (r = 0.80; p < 0.05). These results add to those obtained above and further confirm that these waters are polluted. Taken together, these results demonstrate that the waters at these different sites are unsuitable for any use by the populations living there. The local authorities should implement measures to protect water sources from contamination, in particular by controlling agricultural and domestic discharges.

We would like to thank the authorities of the Ministry of Higher Education, Scientific Research and Innovation of the Republic of Guinea for funding the research.