A new method has been developed to measure the nitrogen isotopes in ammonium and nitrate in natural waters. The process involves using ion exchange to absorb the compounds, distilling the solution to purify them, and then analyzing them with a special instrument. Testing this method on simulated and real water samples showed accurate and consistent results. The values obtained for the nitrogen isotopes in the water samples were very close to the expected values, with small variations. This method requires less water and is quick to perform, making it suitable for field experiments.