A new method for concentrating nitrate from fresh waters for δ¹⁵N and δ¹⁸O analysis has been developed and field-tested for four years. The benefits of the method are: (1) elimination of the need to transport large volumes of water to the laboratory for processing; (2) elimination of the need for hazardous preservatives; and (3) the ability to concentrate nitrate from fresh waters. Nitrate is collected by, passing the water-sample through pre-filled, disposable, anion exchanging resin columns in the field. The columns are subsequently transported to the laboratory where the nitrate is extracted, converted to AgNO₃ and analyzed for its isotope composition. Nitrate is eluted from the anion exchange columns with 15 ml of 3 M HCl. The nitrate-bearing acid eluant is neutralized with Ag₂O, filtered to remove the AgCl precipitate, then freeze-dried to obtain solid AgNO₃, which is then combusted to N₂ in sealed quartz tubes for δ¹⁵N analysis. For δ¹⁸O analysis, aliquots of the neutralized eluant are processed further to remove non-nitrate oxygen-bearing anions and dissolved organic matter. Barium chloride is added to precipitate sulfate and phosphate; the solution is then filtered, passed through a cation exchange column to remove excess Ba²⁺, re-neutralized with Ag₂O, filtered, agitated with activated carbon to remove dissolved organic matter and freeze-dried. The resulting AgNO₃ is combusted with graphite in a closed tube to produce CO₂, which is cryogenically purified and analyzed for its oxygen isotope composition. The 1σanalytical precisions for δ¹⁵N and δ¹⁸O are ±0.05‰ and ±0.5‰, respectively, for solutions of KNO₃ standard processed through the entire column procedure.