Over one hundred years ago, on September 26, 1908, chlorinated water flowed through the taps and into the homes of the 200,000 residents of Jersey City, New Jersey. For the first time, an American city was supplied with drinking water disinfected with the germ-busting chemistry of chlorine. A critical development that led to the routine use of chlorine to destroy germs in drinking water also occurred in 1908: the British scientist Dr. Harriette Chick revealed the laws of disinfection.

Dr. Chick worked at England’s Lister Institute, a center for the study of the cause, prevention and treatment of diseases. While it was known that chlorine could destroy microscopic enemies like bacteria and viruses, Dr. Chick was the first to understand the factors that affect the rates of germ-killing by disinfectants. After 100 years, her work continues to help water treatment operators provide the clean water that rushes into our lives at a turn of the faucet.

Destroying the Germs that Cause Disease

In 1908, Harriette Chick published “An Investigation of the Laws of Disinfection,” a research study in which Chick described the factors that affect the rates of disinfection of germs by agents like chlorine. “Chick’s Law,” later modified by H.E. Watson, says mathematically that killing germs with disinfectants is dependent upon the:

  • Type of disinfectant used
  • Strength of the disinfectant
  • Amount of time the disinfectant is in contact with the germs

Type of germs

The general form of Chick’s Law for any combination of germ and disinfectant details that the longer the contact time between germs and disinfectants, the more germs are killed. Scientists call this type an exponential decline. In addition to germ killing, exponential decline also describes other scientific processes, like natural radioactive decay.

Drinking Water Risks

In the centuries before chlorine was routinely added to water supplies, drinking water diseases killed thousands of people—the powerful and the lowly—every year. Medical researchers believe that Alexander the Great, who ruled most of the known world over a thousand years ago, died of typhoid fever in his early thirties. This “diagnosis” is based on historical reports of Alexander’s symptoms in the period before his death.

Alexander may well have become infected with the bacterium salmonella typhi, which causes typhoid fever, by drinking water containing this invisible germ. Typhoid fever causes a high fever, body aches, abdominal pain and diarrhea. Modern antibiotics like Cipro®—made using chlorine chemistry—are effective against typhoid fever.

A Pioneering Scientist in More Ways than One

In 1905, three years before publishing her landmark research on disinfection, Dr. Chick became the first woman appointed to the staff of England’s Lister Institute. Her appointment was met with some resistance from those who objected to women working in professional careers. Nevertheless, she conducted some of the most important research of her time in the fields of disinfection and nutrition.

The U.S. Centers for Disease Control and Prevention noted recently that Harriett Chick’s contribution to the understanding of disinfection science “quickly paved the way for researchers and scientists to promote widespread disinfection of drinking water.” By 1928, twenty years after its introduction in Jersey City, chlorine was being added to the water supply of virtually every large American city. The public health benefit was clear: Jersey City records show that between 1906 and 1926, the typhoid fever rate declined by more than 92 percent.

Dr. Harriette Chick was a dedicated researcher who worked at the Lister Institute for 65 years until her retirement at age 95. Over one hundred years after her ground-breaking research on disinfection, we celebrate her contribution to a century of clean drinking water.

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