Answer:
During the years of the Black Plague, very few places in Europe had safe drinking water. Most people had to obtain their water from more or less unclean sources, although a few were lucky enough to live in sparsely populated areas with non-existant pollution, or close to pristine water sources like a stream.
The lack of safe drinking water, or better, the abundance of dirty water sources also contributed to spread of the disease in the 14th century, which killed around a third of the European population at the time, in some places killing over half of the population.
