Sand filters already in use for filtering particles out of water can be modified to encourage growth of biofilms that also remove biodegradable molecules. Chlorination of drinking water has been popular in the U.S. for most of this century. It is an inexpensive, broadly effective disinfection method that has the additional advantage of leaving a chemical residual to suppress the growth of microorganisms in water distribution pipes. Since the 1970s, however, chlorination itself has been linked to health problems resulting from reactions with organic matter, either in solution or as particles, in the distribution system. More recently, chlorine has failed to safeguard the water supply against pathogens like Cryptosporidium.
Most people also object to the taste and odor left by chlorine in their drinking water.
Yet, without chlorination, microorganisms in the water distribution system, although not usually health-threatening, produce undesirable tastes, odors, and turbidity. One promising way of producing such biologically stable and better-tasting water is to incorporate biofilm processes into water treatment, enlisting the help of beneficial microorganisms to eliminate the ones that cause disease. References Behm, D. Choose your poison. Chlorination brings risks of its own. Huntoon, E. Cryptosporidium New superbug and dangerous.