Why is domestic use of river water considered safe only after treatment?

Correct answer: Because pollutants can spread diseases

The direct answer is A: pollutants in river water can spread disease, so treatment is needed before domestic use, especially drinking. River water may contain disease-causing microorganisms such as bacteria, viruses, or parasites, as well as chemicals, sewage, pesticides, metals, or suspended dirt. Treatment steps can include screening, settling, filtration, disinfection, and, where needed, additional processes suited to the contaminant. These steps make water safer, although the exact treatment depends on testing and local conditions. Option A is correct because untreated biological and chemical pollutants can harm health. Option B is wrong because clean water is useful and essential for domestic life. Option C is wrong because no river is automatically medicinal; natural-looking water may still contain invisible hazards. Option D is wrong because proper treatment is intended to remove contaminants, not make water salty. The exam idea is simple: natural source does not guarantee safe water; purification and checking are required. Memory cue: river water may look clear but still need treatment.