The analyses of over 2000 drinking water samples from many parts of the United States suggest that most water consumers do not drink water containing large numbers of elongated mineral particles which have lengths three times the diameter. Some drinking waters do contain high amounts of particulate. While it is still to be determined how predictive cell assay tests are of potential health hazards, it is apparent that the suspended particulate fraction of 3 drinking waters has some effect on biological systems. It is important to note that the results of two independent assays show the drinking water particulate to be much less biologically active than commercial asbestos fibers.