Fog drip, or mist precipitation, has generally been neglected by hydrogeologists as a source of water, largely because of the difficulty in tracing fog through the hydrosphere. In the arid climate of northern Kenya, light stable isotopes aided in assessing the importance of fog drip. Fog was collected at localized fog-laden montane areas and determined to have δD values of about +3 to +16.6‰. Rain-derived groundwater was found to have δD values of about -25‰. However, groundwater in the fog-laden areas have δD values of about -12.5‰ and appear to be a mixture of fog and rain. It is thought that in special environments such as northern Kenya, fog drip may be an important source of infiltration and groundwater recharge.