A protozoa is under domain Eukarya. (There are three domains: Bacteria, Archaea, and Eukarya) Bacteria is a domain. Bacteria and Archaea are usually unicellular while Eukarya is usually multicellular.
Protozoans such as Amobae or Paramecium are usually found in habitats of fresh water, marine environments and soil.
Not all protozoans are harmful but some also cause diseases like amoebiasis and malaria.
Don't drink water from just anywhere.
Clean drinking water/potable water is needed simply because our body needs water that is uncontaminated or harmful to us to survive. Imagine drinking toilet water..