Biological parameters of water quality/ Biological characteristics of water

Biological parameters are important factor that determine quality of drinking water. It is more important than physical and chemical parameters in term of direct effect on human health.
Some important biological characteristics affecting quality of drinking water includes bacteria, protozoa, virus and algae.

1. Bacteriological aspects of water pollution:

Human beings and other animals discharge large number of intestinal bacteria into stool and urine. Therefore bacteria appears in drinking water when water source is contaminated with stool.
Some intestinal bacteria which are normal flora of intestine are not pathogenic while other bacteria causes serious disease when they are present in drinking water.
Some pathogenic bacteria includes- Salmonella, Shigella, Vibrio cholera, Yersinea enterocolitica
These bacteria are only present in drinking water if source of water is contaminated with faeces.
Drinking water must be regularly check to detect intestinal pathogens. However all intestinal pathogens are difficult to cultivate and identify in routine examination. Therefore, presence of pathogenic intestinal bacteria is indirectly checked by detecting intestinal normal flora. Such organism which are routinely checked for quality of water is known as indicator organism for faecal contamination.
Some indicator organism are faecal coliform ( E. coli), faecal Streptococci (Enterococcus), Clostridium perfringens

Drinking water must be free from viruses.
Sometime viruses from intestinal tract of infected person get access to water along with faeces.
Some intestinal pathogenic viruses which are transmitted through contaminated water are- Rotavirus, Poliovirus, Hepatitis A and E, etc

Drinking water should be free from disease causing parasites.
Many species of protozoa and helminthes that causes water borne disease contaminates water through stool of infected patients.
Some pathogenic parasites are- Entamoeba histolytica, Giardia, Balantidium coli, etc

Growth of algae in water affects the quality of water by various ways.
Algae gives characteristic color, odor and taste to water. Also algae prevent penetration of light to bottom of water system affecting photosynthetic organisms.
Various algae produces toxic compounds. For examples, Microcystis produces hepatotoxin, Similarly Anaebaena and Nostoc produces neurotoxin. Therefore, drinking water should be free from algae.