The isotope Na{sup 24} is one of the major short half-life constituents of reactor effluent water. It has a half-life of 15 hours and decays of emission of a 1.39 MeV maximum beta particle. Other radioisotopes present in reactor effluent water from which Na{sup 24} must be separated are Si{sup 31}, P{sup 32}, Mn{sup 56}, Cu{sup 64}, As{sup 76}, Sr{sup 91--92}, Ba{sup 139--140} and rare earths. This report describes a rapid and very simple method for the quantitative determination of Na{sup 24} in a radiochemically pure form.