Contaminants that are causing widespread concern as of late are Disinfection By-Products (DBP's). Many believe that DBP's are the single greatest health threat in water supplies. DBP's are contaminants, some of them cancer-causing, that are left behind by the very chemical (chlorine) that utilities use to make their water potable. About 15 years ago scientific testing identified chlorine as a potential health hazard, but it is not the chlorine in itself that is dangerous. Scientists discovered that chlorine reacted with organic material in water, such as decaying leaves, to produce hundreds of chemical by-products, several of which have been proven to be carcinogenic (Trihalomethanes make up the bulk of the cancer-causing DBP's). Other disinfection by-products may cause adverse effects on the liver, and nervous and reproductive systems. The use of chlorine for water treatment to reduce the risk of infectious disease may account for a substantial portion of the cancer risk associated with drinking water.   Trihalomethanes are associated with increased risk of bladder and rectal cancer, possibly accounting for 5,000 new cases of bladder cancer and 8,000 new cases of rectal cancer per year in U.S. According to a study done by the American Water Works Association, more than 230 million people (approximately 90% of America's population) receive disinfected drinking water containing hundreds of disinfection by-products. Given the large number of people who consume chlorinated drinking water, the number of cases of cancer potentially attributable to this exposure is substantial. Since a large percentage of the DBP's are developed after leaving the treatment plan our only viable course of action is point-of-use filtration using an activated carbon filter. Currently carbon filtration is the only known way to get cancer-causing Trihalomethanes and other dangerous disinfection by-products out of our nation's drinking water.