The hydrochemical, microbiological and biochemical assessments of groundwater samples were carried out in some parts of Lagos metropolis, Nigeria, with a view to evaluating the quality of the water of the area. Twenty groundwater samples, at least one from each grid of a gridded map were collected from wells generally below 35 m. Physical parameters (Temperature, Total Dissolved Solids, Electrical Conductivity and pH) were measured on the field using hand-held devices. The water samples were subjected to laboratory analyses in order to determine the concentrations of cations (Na+ K+, Mg2+ and Ca2+), anions (Cl–, SO42-, CO32- and HCO3–) and heavy/trace metals (Fe3+ and Cr3+). The Most Probable Number (MPN) expressed as the number of colonies per 100 ml (col/100ml) was used for the microbial analysis while biochemical tests were carried out on isolates from Eosin Methylene Blue (EMB) plates to reveal the likely organisms present in the water samples. When compared to relevant standards, the concentrations of the ions and other parameters such as EC, TDS and pH show that the water samples are generally suitable for drinking. Parameters such as Kelly’s ratio (KR), Sodium Adsorption Ratio (SAR), Soluble Sodium Percent (SSP) and Permeability Index (PI) indicate that the water in the area is generally suitable for irrigation. Microbiological and biochemical analyses however show that the water samples contain some pathogenic organisms such as salmonella typhi and Shigella spp rendering majority of the water unsuitable for drinking. It is therefore recommended that microbiological and biochemical analyses should always be included for a holistic water quality studies that is intended for drinking.
Key Words: Groundwater, Water quality, Most Probable Number (MPN), Lagos Nigeria, Relevant Standards