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American Journal of Water Resources. 2019, 7(2), 62-75
DOI: 10.12691/ajwr-7-2-4
Open AccessArticle

Water Quality Index for Assessment of Potability of Groundwater Resource in Langata Sub County, Nairobi-Kenya

EA Ochungo1, , GO Ouma2, JPO Obiero3 and NA Odero4

1Institute for Climate Change and Adaptation (ICCA), University of Nairobi, Nairobi, Kenya

2Department of Meteorology, University of Nairobi, Nairobi, Kenya

33Schools of Engineering, University of Nairobi, Nairobi, Kenya

4Department of Electrical and Electronics Engineering, Machakos University, Machakos, Kenya

Pub. Date: June 04, 2019

Cite this paper:
EA Ochungo, GO Ouma, JPO Obiero and NA Odero. Water Quality Index for Assessment of Potability of Groundwater Resource in Langata Sub County, Nairobi-Kenya. American Journal of Water Resources. 2019; 7(2):62-75. doi: 10.12691/ajwr-7-2-4


Water Quality Index (WQI) computation method based on quality parameters’ selection, assigning of weights, creation of sub-indices and calculation of the aggregated quality value has been used for many decades from the early 1960s to check on the pollution stati of watersheds. Today, due to rising water demand in the face of increased drought induced water shortage challenges and rampant pollution of the water sources, consumers augment their needs by using groundwater resources like in the case of Langata sub County in Nairobi city-Kenya. Little however, has been done to assess the overall potability of groundwater quality here. Accordingly, in the present study, a Water Quality Index (WQI) was developed by Weight Arithmetic Water Quality Index (WAWQI) method to fill that identified gap using a five categories’ grading scale, viz. excellent (A), very good (B), good (C), fairly good (D), suitable (E) and unsuitable (F). To realize this, chemical parameters’ concentration ranges were defined on the basis of the Kenyan Standards (KS) and International Standards of World Health Organization (WHO).Subsequently, a total of eight chemical parameters were selected based on their level of occurrence in borehole commissioning data obtained from Water Resource Management Authority’s database of the area viz; K+, Na+, Ca2+, Fe2+, F-, Cl-, SO4-2 and Ec (µS/cm). Out of a total of 137 boreholes, only 39 had complete eight chemical parameters. These 39 boreholes’ water quality assessment is taken in this study as a true representation of the entire area’s groundwater quality. The individual concentrations were spatially plotted using Surfer Software’s digital terrain model (DTM) which produced contoured maps in different chroma saturations including the overall aggregated concentration to facilitate scale ranking. The WQI for the study area is 53.18 in a scale of 1 to 100, with one being excellent. In this case, the groundwater quality was ranked as grade ‘C’. WQI calculation method is known to improve the understanding of water quality issues by integrating a suite of data into a single value which describes the status of water quality. WQI is very useful for the water management authorities because it facilitates their informing of the public on water quality in a simplified form.

index water potability quality

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