What was the most serious health concern caused by the poor sanitation and contaminated water supplies in 19th century tenements?

Poor sanitation allowed sewage and waste to contaminate drinking water. This spread cholera, a dangerous disease that caused severe diarrhea and could lead to death, making a cholera epidemic the most serious health concern. Dirty conditions and odors were unpleasant, but they were not as immediately life-threatening.

AI-written and checked against the verified answer.