Abstract: A portable, hand-held instrument is provided for capturing a predetermined volume of water to be tested and transferring a measured quantity of reagent into the water for making a visual test of a water condition. A slide is included which has a measuring chamber having a size defining a predetermined volume of reagent. This slide is shiftable from a loading position in which water may be introduced into a mixing chamber and reagent from a supply chamber fills the measuring chamber, to a mixing position where the measuring chamber is isolated from the reagent supply chamber but is in communication with the mixing chamber for mixing the reagent with the water sample. Ports existing in the side of the instrument allow for the introduction of the sample water. Doors are attached to the slide which leave these ports uncovered when the slide is in the loading position and which cover them when in the mixing position.