The identification of a number of mutagenic and carcinogenic chemicals in our public water supplies has raised concern over potential genetic and carcinogenic hazards to the human population. There is growing evidence to indicate that these chemicals are produced during water chlorination, and consequently alternative strategies for water disinfection are being considered. Unfortunately, it is not known to what extent the mutagenic activity in chlorinated drinking water, and the associated potential health risks, are accounted for by chemicals identified thus far. The authors laboratory has been exploring the use of humic acid for studying the mutagenic and carcinogenic properties of disinfection by-products. The present report extends our findings on the mutagenic properties of chlorinated humic acids in the Ames test and includes results from studies on the ability of chlorinated and non-chlorinated humic acids. Studies are also being conducted on the toxicological properties of drinking water samples prepared using alternative techniques for disinfection and post-disinfection treatment. Preliminary results on the mutagenic activities of these samples are discussed.