The Water Neutron Detector (WaND) is an efficient and non-toxic alternative to some helium-3 neutron counting applications. The detection volume is comprised of a 1.02 cubic meters homogeneous mixture of deionized water doped with 0.5% gadolinium chloride. Following neutron capture, gadolinium emits an 8 MeV gamma shower, which in turn creates Cherenkov light that can be detected with photomultiplier tubes. The WaND is particularly well-situated to perform multiplicity counting of small samples because of its high efficiency of (23.4 +/- 0.8)% and short die-away time (15 microseconds). Due to the moderate gamma sensitivity, the WaND system may be suited for neutron-based nondestructive assay of small quantities of spent fuel. It is effective at measuring and identifying minute quantities of plutonium. Using a novel algorithmic approach, the WaND system can effectively differentiate between Cf-252 and Pu-240, as well as quantify the mass of Pu-240 in milligram quantities.