The type of traps commercially available for determination of water by distillation of samples with an immiscible liquid of low density, such as toluene, are in some respects unsatisfactory. With a trap such as that of Bidwell and Sterling having a graduated portion with a bore sufficiently small to obtain reasonably precise readings of small volumes, sharp separation of the immiscible liquid and the water often does not occur even when the trap has been carefully cleaned. Sharp separation usually occurs in traps that have graduated tubes of larger bore, but this involves a sacrifice of precision in reading the volume of water. A third trap combines the advantages of both types. The lower portion of the graduated part is open and attached to a rubber tube connected to a leveling bottle or funnel containing mercury.