In this paper, six methods of preconcentration on ion exchange or chelating filters and resins for neutron activation with
X-ray and gamma spectrometry are described. These techniques are applied to the determination of trace elements in natural
waters. The analysis of water samples from the lake of Geneva by these different methods gave results in good agreement among
themselves and also when compared with those obtained by other techniques, with a very reasonable blank and good sensitivity
for most determined elements.