Water Supply – Distribution - Math Matters - Maplesoft

Math Matters

Water Supply & Distribution

The 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 important.

Chick’s Law was later modified by H.E. Watson (1908) to include the coefficient of specific lethality . The Chick-Watson Equation is shown below.


initial number of organisms

number of organisms at time t

concentration of disinfectant (mg/L)

contact time (min.)

coefficient of specific lethality

coefficient depending on
disinfectant type and pH

Harriet 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.
Abel Wolman
(American, 1892-1989) perfected the formula for the chlorination of urban water supplies with chemist Linn H. Enslow.
Carl Wilhelm Scheele
(Swedish, 1742- 1786) discovered chlorine in 1774.