[en] We measured the yield of ¹⁵O, ¹¹C and ¹³N by photonuclear reactions in water exposed to bremsstrahlung gammas produced with a 1 GeV linac.The activity at saturation reached the values, respectively, of 30, 1.17 and 4.4.10^-1 mCi μA^-1cm^-3 of water. We describe the measurements and possible implications and we compare the experimental results with calculations performed with the Monte Carlo code GEANT. (orig.)