The purpose of this study was to determine whether plant activated mutagens could be detected and quantitated from drinking water samples obtained from the Rathbun Rural Water Association. Plant activation refers to the process in which a non-mutagenic agent is transformed by biological action of a plant into a mutagen. Water samples collected were fractionated and concentrated with a 0.2 m tangential flow ultrafiltration membrane, then passed through a NA+ charged cation column. Aliquots were taken after the 0.2 m filter and cation exchange to measure DOC adsorption. The sample was then passed through in a series, a polysulfone 30 kDa ultrafiltration membrane, a poly sulfone 1 kDa ultrafiltration membrane, and a polyamide reverse osmosis membrane. A mass balance analysis based on total organic carbon was conducted on the drinking water and each size fraction. Weak positive responses were observed in one 1 kDa retentate and in two reverse osmosis retentates. In all three cases, there was an initial yet weak statistically significant increase in the mutagenicity of the tested samples. The research concluded that concentrated fractions of Lake Rathbun were rather benign. Even after many fold concentration and analysis with highly sensitive Salmonella mutation tester strains, only a weak positive response was observed with two fractions.