Residual chlorine after chlorination of drinking water should measure after?

NORCET-7 Mains-2024

Community Health Nursing

Easy

Appeared in: NORCET-7 Mains-2024

Explanation

The correct contact time for measuring residual chlorine is 60 minutes (1 hour).
This duration is specified to ensure that the disinfection process is complete and effective against a wide range of pathogens, including bacteria and viruses.
According to standard public health texts, the presence of free residual chlorine for at least one hour is essential for safe drinking water.
The minimum recommended concentration of free residual chlorine after this one-hour period is 0.5 mg/L.

Option B: While 30 minutes may be cited as a minimum in some rapid or emergency guidelines, it is not the standard recommended time for ensuring complete disinfection, especially against more resistant viruses.
Option C: A contact time of 15 minutes is insufficient for chlorine to effectively neutralize all pathogenic organisms in the water. This short duration poses a significant risk of waterborne diseases.
Option D: A 120-minute (2-hour) contact time is unnecessarily long for routine measurement of residual chlorine. While it does not harm the disinfection process, it is not the standard practice and delays the availability of water.

Visual 1: Flowchart: Steps in Water Purification. This visual would illustrate the sequence from raw water intake, through coagulation, sedimentation, filtration, and finally disinfection, highlighting where and when chlorine is added and tested.
Visual 2: Infographic: Breakpoint Chlorination Curve. This graph would help explain the concept of chlorine demand, the destruction of chloramines, and the establishment of a free chlorine residual over time.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Water purification and disinfection standards as background academic context rather than a clinical decision trigger.
Ensuring safe drinking water is a cornerstone of public health nursing, directly preventing outbreaks of waterborne diseases like cholera, typhoid, dysentery, and hepatitis A.
Community health nurses play a vital role in educating the public on safe water practices, including household-level chlorination, especially during emergencies like floods or earthquakes.
What if the water is highly turbid (muddy)? If the water is turbid, the effectiveness of chlorine is drastically reduced. The nurse should first advise filtering the water through a clean cloth or allowing sediment to settle before attempting chlorination. The chlorine dose and contact time may also need to be increased.

How to Approach the Question

First, identify the core question: It asks for the standard time to wait before measuring residual chlorine in drinking water.
Recognize this as a factual recall question based on public health standards.
Scan the options: 15, 30, 60, and 120 minutes. These are all plausible timeframes, so precise knowledge is required.
Recall the principle of 'contact time' in disinfection. This is the minimum time needed for the disinfectant to work.
Access knowledge about water purification guidelines. The standard contact time ensures a balance between effective pathogen killing and practical water treatment operations.
Select the option that aligns with the established standard for ensuring safety against both bacteria and more resistant viruses, which is 60 minutes.

Concept Tested & Keywords

Q6h7d189pI3v_GAs_u-8ir