protection of public health from the transmission
of waterborne diseases by disinfecting water has been
recognized since the early 1900’s. Of the existing
processes used to produce safe drinking water, chlorination
of public water supplies ranks as one of the most
Chick (British, 1875-1977) developed Chick’s Law in 1908.
This law gives the relationship between
the kill efficiency of organisms and contact
time with a disinfectant.
1892-1989) perfected the
formula for the chlorination of
urban water supplies with chemist
Linn H. Enslow.
Wilhelm Scheele (Swedish,
1742- 1786) discovered chlorine
Law was later modified by H.E. Watson
(1908) to include the coefficient of specific
The Chick-Watson Equation is shown below.