Question 1

What is CT in water treatment?

Accepted Answer

CT is the product of disinfectant residual concentration and contact time. It is the EPA Surface Water Treatment Rule metric for inactivating Giardia and viruses.

Question 2

What is a good CT value?

Accepted Answer

CT achieved must equal or exceed the CT required from the EPA table for your pH, temperature, and target log inactivation. 3-log Giardia at 10 °C and pH 7.0 with 1.0 mg/L free chlorine requires roughly 73 mg/L·min.

Question 3

What is the baffling factor?

Accepted Answer

Baffling factor (0.1 to 1.0) accounts for short-circuiting in the contact basin. Common values are 0.3 for hydraulic basins and 0.7 for serpentine pipes.

Question 4

How do I increase CT?

Accepted Answer

Raise chlorine residual, lower flow, add baffles, or pre-chlorinate further upstream to extend the contact zone.

CT Value Calculator – Disinfection Compliance