A liter is equivalent to about one quart. Microorganisms are very small animals and plants that are too small to be seen by the naked eye and must be observed using a microscope. Microorganisms in water include algae , bacteria , viruses , and protozoa . Algae growing in surface waters can cause off-taste and odor by producing the chemicals MIB and geosmin. Certain types of bacteria, viruses, and protozoa can cause disease in humans.
Bacteria are the most common microorganisms found in treated drinking water.
The great majority of bacteria are not harmful. In fact, humans would not be able to live without the bacteria that inhabit the intestines. However, certain types of bacteria called coliform bacteria can signal the presence of possible drinking water contamination. A milliliter is one one-thousandth of a liter. A liter is a little more than a quart.