A Brief History of Drinking Water Treatment

• Water has been "treated" for many centuries. First, it was filtered and boiled so that it would look and taste better. These treatments also made the water safer, although no one knew it.
• Eventually, scientists discovered that water could contain harmful bacteria that caused diseases. These "pathogens" were too small to be stopped by filters alone. A disinfectant was required to kill pathogenic micro-organisms.
• The transmission of certain infectious diseases through drinking water has been a recognized public health problem since before the turn of the century. The presence of these organisms in water led to the frequent transmission of such deadly diseases such as cholera, typhoid, dysentery and hepatitis.
• Due to improvements in the source and treatment of water supplies, these diseases have been virtually eliminated in the world's modern drinking water. Chlorine was first used as a water disinfectant in Europe and America in the early part of the 20th century. Since then, widespread epidemics of these most severe forms of disease no longer occur.
• Still, microbiological organisms remain as a residual problem in some water supplies. Transmissible diseases such as Hepatitis A are an important concern, as well as some micro-organisms that can cause acute and chronic gastrointestinal disorders. A cholera epidemic in Columbia, South America last year was caused from inadequate disinfection.

• Congress enacted the Safe Drinking Water Act (SDWA) in 1974. The law was amended in 1986 to expand the Environmental Protection Agency's (EPA's) role in protecting public health from contaminated drinking water. The amendments require the agency to enforce control of specific disease-causing organisms and indicators that may be present in drinking water, and require public water systems to disinfect their water.
• Chlorine, in the form of di- or tri-chloramines, is the same active ingredient used in household bleach. It is the most commonly used disinfectant for public drinking water supplies and swimming pools.
• Chlorine gas is used in 90 percent of all water disinfection applications. Chlorine must react with the water for a certain period of time. This reaction time period is called contact time. For most water systems, the best contact time is usually 30 minutes.
• A certain amount of chlorine must remain in water after treatment to ensure continued protection against harmful organisms. This remaining chlorine is known as a chlorine residual.
• Chlorine destroys harmful organisms in two steps:
  (1) Chlorine molecules penetrate the cell wall of the harmful organism, and
  (2) The organism's enzymes react with the chlorine and destroy the organism.
• Chlorine can combine with natural organic compounds in raw water to create some undesirable by-products. These by-products are regulated by the Safe Drinking Water Act (SDWA).