Water used for domestic and drinking purposes in agricultural communities is still extracted from the groundwater using shallow tube wells. However, its quality is threatened by contamination due to chemical residues that were not fully utilized in a rice production system. These residues eventually go with the water as it is distributed in the whole area, with some amount reaching the groundwater. In this study, the rate of chemical fertilizers and pesticides applied by farmers and the possible level of groundwater contamination was determined. The information obtained maybe used in the formulation of strategies for future monitoring of the presence and level of concentration of chemical residues and regulation of the usage of agricultural chemicals in the Upper Pampanga River Integrated Irrigation Systems (UPRIIS). Results revealed that farmers in the UPRIIS service area used chemical fertilizers at the rate of 69-173 kg N per ha, 26-32 kg P per ha and about 30 kg K per ha. These application rates were high as compared to recommended rates, particularly in Districts IV and V of the UPRIIS service area. Similarly, majority of the farmers (60-80%) were using molluscicides, herbicides, insecticides and fungicides in preventing and controlling pests in their crops. Analysis of the quality of groundwater samples indicated that values obtained were within tolerable limits when compared to the standards for drinking water. The mean values of K concentration, which was found to be statistically different between the districts also exhibited strong relationships with PO43-, Na+ and NO3-. The other parameters of water quality showed no significant differences between and among the districts. While the observed values were within the tolerable limits, monitoring of their levels must regularly be done to safeguard the quality of groundwater.