Dr John Snow - unravelling a mystery

The transcript details an investigation into a Cholera outbreak linked to the Broad Street pump. Initially, there was no apparent connection between the victims and the pump. However, it was discovered that a woman who had moved away from Broad Street still consumed its water, leading to her and her niece's deaths. The investigation concluded that the pump was the contamination source, evidenced by white flecks in the water.

What did the author find in the sample of pump water?

What was believed to be the source of contamination in the pump water?