Nitrate often pollutes groundwater resources due to excessive use of fertilizers or on land by wastewater deposition and can therefore limit the direct use of groundwater for drinking purposes. Water analysis from water boreholes in Northern coastal aquifers of Peloponnese (Diakopto municipality), during the last year, showed that nitrate concentrations were higher than 50 mg L-1. We propose that the high nitrate concentration accrued from leaching of nitrogen fertilizer residuals used in agricultural practice remain in cultivated soils at the end of growing seasons. The main horticultural crops in this area are irrigated olive and citrus groves, fertilized by relatively high amounts of nitrogen fertilizers. Geological and hydrological data of these areas favors the conversion of nitrogen substances into nitrates that leach into groundwater.