Option 1: The coliform bacterial count allowed by ISI for inland and surface water for public supply is not more than 40 bacteria per 100 ml. This means that the water is considered safe for consumption if it contains less than or equal to 40 coliform bacteria per 100 ml.

Option 2: The coliform bacterial count allowed by ISI for inland and surface water for public supply is not more than 30 bacteria per 100 ml. This option suggests a stricter limit compared to option 1. However, it is not the correct answer.

Option 3: The coliform bacterial count allowed by ISI for inland and surface water for public supply is not more than 20 bacteria per 100 ml. This option suggests an even stricter limit compared to options 1 and 2. However, it is also not the correct answer.

Option 4: The correct answer. The coliform bacterial count allowed by ISI for inland and surface water for public supply is not more than 10 bacteria per 100 ml. This option indicates the strictest limit, implying that the water must contain less than or equal to 10 coliform bacteria per 100 ml to be considered safe for consumption.

In conclusion, the correct answer is option 4, where the maximum