Which of the following diseases is not transmitted by unsafe water?

Measles is caused by a virus and primarily spreads through respiratory droplets when an infected person coughs or sneezes. It is not transmitted through water, unsafe or otherwise. This distinguishes it from the other diseases listed, which are all associated with contaminated water sources.

Typhoid, dysentery, and polio are diseases that can be contracted through consuming or coming into contact with water contaminated by pathogens. Typhoid fever is caused by the bacterium Salmonella typhi, dysentery can be caused by either bacteria or protozoa found in contaminated water, and polio is caused by the poliovirus, which can also be spread through fecal contamination of water sources.

Understanding the modes of transmission for these diseases is crucial for implementing effective public health measures, especially in areas where water quality may be compromised.