Table 5.

Factors affecting water disinfection with halogens.

Factor	Impact	Common instructions	Alternative means to compensate	Reference
Concentration (primary factor)	Inversely correlated with the relationship quantified by their product (disinfection CT constant), which specifies inactivation of specific microorganisms	Higher concentrations are more effective	Lower concentrations can be used with longer contact times. Taste becomes distinct above 2–3 mg·L−	Table 4 and 141
Time (primary factor)		Assumed priority is to minimize contact time
Temperature (secondary factor)	Cold water slows chemical disinfection reaction	Increase concentration of disinfectant	Extend contact times
Organic contaminants (secondary factor)	React with halogens to form compounds with little or no disinfecting ability, decreasing the concentration of available halogen	Double the amount of chlorine or iodine in cloudy water	Clarify water to remove contaminants. (C-F, filtration, sedimentation); Due to the difficulty in estimating halogen demand, it is prudent to use 3–4 mg·L−1 as a target halogen concentration range for clear surface water. Lower concentrations (eg, 2 mg·L−) can be used for backup treatment of questionable tap water or high quality well water	Tables 6 and 7 and 36,52,87,169–171

C-F, coagulation–flocculation.