Which organism is commonly associated with contaminated water?

• A. Giardia
• B. Vibrio cholerae
• C. Norovirus
• D. Entamoeba histolytica

Answer: (A)

Waterborne pathogens and how they spread through contaminated water are being tested here. Giardia is a protozoan parasite that forms hardy cysts, which can survive in water for long periods. When people drink water containing these cysts, they can develop giardiasis, with symptoms like diarrhea and abdominal cramps. The cysts’ resilience means untreated or inadequately treated water from sources such as lakes, streams, or wells is a classic route of transmission, and Giardia is the organism most commonly linked to this scenario.

Vibrio cholerae also causes illness from contaminated water, notably cholera, which is tied to water and sanitation conditions, but the common teaching emphasizes Giardia as the prototypical water-associated organism in many everyday exposure contexts. Norovirus and Entamoeba histolytica can spread via contaminated water too, but Giardia’s distinctive cyst form and frequent occurrence in untreated drinking water make it the best match for this question.