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Despite the ability of aquifers to filter bacteria in wastewater, application rates exceeding the land's capacity to adsorb enteric microorganisms may result in contamination of water resources. We measured total coliform (TC) and fecal coliform bacteria (FC) in groundwater flowing from basalt and sand aquifers in wells into aquifers, irrigation water and river water monthly for one year. TC and FC numbers were higher in irrigation water than groundwater indicating that soil and sediment filtered most of these bacteria before it entered the aquifers. TC and FC numbers in groundwater were generally, but not always higher in the faster flowing basalt aquifer than the sand aquifer. At least one coliform bacteria was found in groundwater from both basalt and sand aquifers showing that groundwater is not necessarily safe for human consumption. FC bacteria were several fold lower in groundwater than river water showing that groundwater is safer than surface water.