Which method is considered unsafe for purifying drinking water in a survival situation?

The method of removing all visible debris from water is considered unsafe for purifying drinking water in a survival situation because this action does not effectively eliminate harmful pathogens or contaminants. While it can improve the water's appearance, visible debris may not represent the full spectrum of dangerous microorganisms, chemicals, or toxins present in the water.

In survival scenarios, methods like boiling water, using chemical purification tablets, and employing water filters are all effective means to properly purify water. Boiling for at least five minutes can kill most pathogens, including bacteria and viruses. Chemical purification tablets can deactivate harmful organisms, and water filters can physically remove many types of contaminants, making these methods reliable options. Therefore, simply removing visible debris does not provide adequate safety for drinking water.