Abstract: Methods and systems for detecting occult blood and other analytes in the water of a toilet bowl release a dye reagent into the water which produces an observable signal in the presence of the blood. The dye reagent is preferably dispersed as a liquid, powder, gel, or other form which rapidly mixes and combines with the sample. Usually, automatic mechanical or electromechanical dispensing systems are used to release the dye reagent into the water.