A water sampling device and method for use with a radiation probe. The device includes a base, filtrate reservoir, filter media support disc, and sample reservoir. The sample reservoir may be interchanged with a radiation probe adaptor. The device and method provide a simple and convenient means to separate particulate solids from a water sample prior to measuring radioactivity without the need for a heat source or electrical power to evaporate the water. The device and method can be used with a variety of commercially available radiation probes and is suitable for field applications.