Question

What should be the count of E. coli in any sample of 100 ml of drinking water ?

• A. 0
• B. 10
• C. 50
• D. 100

Hint:

Drinking water bacteriological standard to memorize:
- E. coli: Strictly 0 per \(100 \text{ ml}\) of sample.
- Total Coliforms: Also must be 0 per \(100 \text{ ml}\) for treated piped water.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Drinking water quality standards are established to protect public health from waterborne pathogens.
Escherichia coli (E. coli) is a bacterium that resides in the intestines of warm-blooded animals.
It serves as the primary indicator organism for fecal contamination in water systems.

Step 2: Detailed Explanation:
According to international guidelines established by the World Health Organization (WHO), as well as national standards such as the Bureau of Indian Standards (IS 10500) and the US EPA:
E. coli or thermotolerant coliform bacteria must not be detectable in any \(100 \text{ ml}\) sample of drinking water.
Therefore, the acceptable count of E. coli in a \(100 \text{ ml}\) sample is strictly \(0\).
The presence of even a single E. coli cell indicates recent fecal contamination.
This implies a high risk of co-occurrence with dangerous waterborne pathogens such as Salmonella, Shigella, and enteroviruses.
Water testing laboratories use membrane filtration or enzyme-substrate tests (like Colilert) to verify the absolute absence (\(0 \text{ CFU/100 ml}\)) of these indicator bacteria before certifying water as potable.

Step 3: Final Answer:
The count of E. coli in any sample of \(100 \text{ ml}\) of drinking water must be \(0\).