Which of the following conditions is typically caused by exposure to contaminated water?

Leptospirosis is primarily caused by exposure to water contaminated with the Leptospira bacteria, which are typically found in the urine of infected animals. This disease is often associated with water sources that may have been contaminated by livestock or wild animal feces. When humans come into contact with this contaminated water, particularly through cuts in the skin or mucous membranes, they can contract the disease.

In contrast, the other conditions listed are caused by different pathogens and associated with different exposure routes. Anthrax is caused by Bacillus anthracis, typically linked to handling infected animal products. Legionnaires' disease is a form of pneumonia caused by inhaling aerosols from contaminated water sources, particularly in man-made water systems, but it does not arise directly from drinking contaminated water. Tularemia is caused by Francisella tularensis and generally results from contact with infected animals or vectors such as ticks, rather than water exposure.

Understanding the specific routes of transmission for each disease highlights why leptospirosis is the correct choice in this context as it is uniquely associated with contaminated water exposure.