2.2.1  Waterborne diseases

Waterborne diseases are caused by people ingesting water contaminated by human or animal faeces containing pathogens. Such diseases can also be caused by food that has been prepared using water contaminated with pathogens. The diseases are caused only when the infectious agent enters the body. Waterborne diseases include most of the enteric (related to the intestine) and diarrhoeal diseases caused by bacteria and viruses. Bacteria are unicellular organisms (made of one cell) and are very small, ranging from 0.5 to 5.0 micrometres (µm) in size. When seen under a microscope, they have different shapes, such as spheres, rods, or spirals. Viruses are microscopic infectious particles, much smaller than bacteria, that can only reproduce when inside the living cells of organisms. Waterborne diseases also include some caused by protozoa (single-celled micro-organisms that are much larger than bacteria, usually between 10 and 50 µm) and helminths. Helminths is a general term for worms, usually applied to those that are parasites on humans and other animals. Table 2.1 shows examples of waterborne diseases and their causes.

Table 2.1  Examples of waterborne diseases.

Category of infectious agentDiseaseInfectious agent
BacterialCholeraVibrio cholerae
Bacterial dysenteryCampylobacter jejuni
(Acute) gastroenteritisVarious
ShigellosisShigella species
Typhoid feverSalmonella typhi
ViralViral gastroenteritisRotavirus and others
Viral hepatitis Hepatitis A and E viruses
PoliomyelitisPolio virus
ProtozoalAmoebic dysenteryEntamoeba histolytica
CryptosporidiosisCryptosporidium
GiardiasisGiardia lamblia
HelminthsAscariasis (roundworm)Ascaris lumbricoides
Dracunculiasis (Guinea worm)Dracunculus medinensis
Trichuriasis (whipworm)Trichuris trichiura

Although drinking contaminated water is a very significant route of transmission for many of the diseases listed above, they may also be transmitted by other means such as by eating contaminated food. Food can become contaminated by poor hygiene during preparation. Flies are also important transmitters of contamination from faeces to food. There are other possible routes of transmission, including through droplets and aerosols, if these are ingested. We use our fingers for eating and frequently put our hands to our mouths; touching contaminated surfaces can also be a route for disease transmission.

  • How could poor personal hygiene by people preparing food cause disease?

  • If cooks do not thoroughly wash their hands before touching food, they could easily transfer contamination by infectious agents. When the contaminated food is eaten, this could transmit disease to the consumers.

In all these cases, the origin of the contamination is faeces of people who are already infected by the disease. Some diseases may be transmitted via the faeces of infected animals. In places without adequate sanitation and where people defecate in the open, waterborne disease is far more likely to occur. By sanitation, we mean the prevention of human contact with wastes. If faeces are effectively separated from people then the transmission routes of waterborne diseases are cut off.

2.2  Diseases associated with water

2.2.2  Water-washed diseases