The coliform count in drinking water is done to ascertain fecal contamination. Coliform bacteria are a group of bacteria that are found in the intestines of mammals, including humans. The presence of coliform bacteria in drinking water indicates that there may be fecal contamination, which could potentially contain harmful pathogens such as bacteria, viruses, or parasites.

Option 2: Assessing the hardness of water is not the purpose of measuring coliform count. Hardness refers to the concentration of magnesium and calcium ions in water, which can cause scaling and interfere with the effectiveness of soaps and detergents.

Option 3: Determining the effect of chlorination is not the primary purpose of measuring coliform count. Chlorination is a method of disinfecting water to kill or inactivate pathogens, including coliform bacteria.

Option 4: Estimating the amount of suspended impurities is not related to coliform count. Suspended impurities typically refer to solid particles or substances that are visibly floating in the water, such as sediment or debris.

Therefore, the correct answer is option 1, as measuring coliform count in drinking water is specifically done to identify the presence of fecal contamination.