The reaction O17(n, p) and the previously unreported reaction O18(n, d)were found to be responsible for the production of the 4.14-second delayed-neutron precursor, nitrogen-17, in water irradiated in a reactor. The effective cross sections of these reactions with fission-spectrum neutrons were measured by counting the delayed neutron emission of irradiated water samples enriched with oxygen-17 and -18. The values obtained are 7.4 ± 0.6 and 0.086 ± 0.008 µb respectively.