Impact of Pit latrines on Groundwater Quality: A comparative study of boreholes and protected springs in Mpigi Town Council, Uganda

Abstract

Pit latrines have increasingly become a threat to domestic groundwater supplies. The major issue of concern is not the use of these pit latrines, but having both pit latrines and groundwater within the same system boundary. This study assessed the impact of pit latrines on groundwater quality by performing a comparison of boreholes and protected springs. The objectives of the study were to assess the vulnerability of the boreholes and protected springs to faecal contamination. To assess the physical, chemical, and microbial quality of groundwater in relation to drinking water. The study also analysed the relationship between faecal indicator parameters with setback distances and the number of pit latrines. The results from the sanitary risk survey revealed that the protected springs were more vulnerable to faecal contamination than boreholes due to a higher number of risk factors such as pit latrines within 10 m, animal grazing near water sources, presence of waste dumps as well as surface runoff. Pit latrines affect the groundwater sources by changing the concentrations of the water quality parameters. The main faecal indicator parameters considered in this study were chloride, nitrate, and E. coli. While pH, colour, TSS, turbidity, colour, and TDS were also analysed as they affect the concentration of the faecal indicator parameters within the water. The mean values of the parameters from both protected springs and boreholes were as follows; pH (5.77 and 5.35 respectively); EC (156.53 and 108.18 µS/cm respectively); colour (13.25 and 428 Pt-Co respectively); TDS (125.67 and 155.52 mg/L respectively); TSS ( 1.00 and 100.17 mg/L); chlorides (5.14 and 2.36 mg/L); nitrates (75.53 and 38.83 mg/L respectively); E. coli (2952 and 102 CFU/100 ml). These water quality parameters were compared with set standards by UNBS (2014) and WHO (2011) for drinking water, some parameters i.e. colour, nitrates and E. coli showed great variations from the recommended standard values, which suggests that some of the sampled groundwater sources are unsuitable for drinking purposes. Further analysis of the concentrations of the faecal parameter indicators with the number of pit latrines revealed that whilst both the protected springs and boreholes are improved water sources, they are likely to be contaminated if subjected to a significant pollution load. Furthermore, in relation to the setback distances, for boreholes within basement aquifers, a distance of 10 m was enough to reduce contamination from the pit latrines given these latrines were located down gradient of the borehole. For protected springs, the effect of pit latrines was still experienced 200 m away. Therefore, the findings of this study emphasized the vulnerability of the shallow groundwater to faecal contamination.