Tritiated process water is monitored by detecting the D2O component via the 2D(γ,n)1H reaction. A probe containing a 1- to 7-mCi 24Na (15-h) gamma source and six 3He neutron detectors produces and monitors the 2D(γ, n)1H reaction. A variety of probe configurations were examined for D2O detection sensitivity. The corresponding detection limits range from 6 to 280 µl for D2O droplets and 1 to 13 µl/cm for D2O streams, when 10-min neutron counting with a 1-mCi gamma source is used. Results from two field applications illustrate the utility of the monitor.