Operator terms · Water and wastewater
What is contact time (CT) in disinfection?
Contact time is how long a disinfectant stays in contact with water before it is used, and CT is that time multiplied by the disinfectant concentration. Enough CT is what actually inactivates pathogens: a high dose with too little time, or the reverse, may not disinfect. Operators design for the required CT.
Last reviewed 2026-08-03
Why both parts matter
Disinfection needs both concentration and time. A strong dose that contacts the water only briefly may not finish the job, and a weak dose given plenty of time may not either. CT captures the trade.
How systems get enough
Contact basins and long pipe runs give water time with the disinfectant before it reaches customers, so the required CT is met.
Common questions
- What does CT stand for?
- Concentration times time, the disinfectant contact measure.
- Why is time important?
- Disinfectant needs enough contact time to inactivate pathogens, not just a high dose.
- How is contact time provided?
- By contact basins and pipe travel time before the water is used.