The kingdom of Saudi Arabia is challenging the extreme water demands and deficiency of water resources. Al Qassim Province is characterized by intensive agricultural utilities and in turns great water supply that irrigated mainly from the Cambrian-Ordovician Saq Aquifer. The present study, based on hydro-chemical data from 26 groundwater wells, focus on assessing the groundwater quality and allocating the best borehole locations. These goals achieved through comprehensive hydro-chemical analyses of water samples. The suitability of the groundwater for drinking and irrigation purposes was assessed, based on hydro-chemical data, according to the standard guideline's values. The results indicate that the Cambrian-Ordovician Saq aquifer is the crucial aquifer in the province, which is detached into two sub-aquifers. The upper sub-aquifer is encountered at depths range from 110m to 130m bgl (below ground level), with overall thickness ranges from 200 to 250 m. The total dissolved solids (TDS) vary from 400 to 800mg/l indicating fresh-brackish water-bearing zones. The lower sub-aquifer is located at depths range from 360m to 400m, with extra saline water characteristics rather than the upper ones, with TDS variance from 600-1425mg/l. Water quality indices include such: sodium content (SC); Chloro-alkalinity index (CAI); sodium adsorption ratio (SAR); and Corrosively Ratio (CR) appraise the suitability of groundwater for municipal activities, agricultural purposes and irrigation utilities. Preceding exploitation further studies and simulation are highly recommended to establish a sustainable level of abstraction besides assessing the vulnerability to protect from pollution.