Assurance that water is microbially safe has traditionally been determined by measuring bacterial indicators of water Quality, most commonly coliforms and Escherichia coli (E. coli). The number of different types of pathogens (disease causing organisms) that can be present in water as a result of pollution with human or animal faeces is very large and it is not possible to test water samples for each specific pathogen.
The presence of E. coli in water is still considered to represent the presence of faecal pollution and is used to indicate that pathogenic bacteria, viruses and protozoa may also be present. The user of water containing pathogens may be at risk of developing a water-related disease if the pathogen is ingested.
More than 100 years ago scientists discovered that human faeces contained bacteria which, if present in water, indicated that the water was not safe to drink. Escherich in 1885 observed two types of organisms present in faeces, one of which he named Bacterium coli (B. coli, which is now called Escherichia coli) - the concept that the presence of B. coli implied pollution of water was readily adopted at that time and is still accepted to date.
E. coli (or alternatively thermotolerant (faecal) coliforms) are the most commonly used bacterial indicator of faecal pollution. E. coli are bacteria which normally inhabit the digestive system of all warm-blooded animals, including humans. E. coli are found in water wherever the water is contaminated with faecal waste of human or animal origin. lt is well recognised and reported that E. coli is the only coliform that is an exclusive inhabitant of the gastrointestinal tract. Most other coliforms have an environmental origin and include plant pathogens and normal inhabitants of soil and water environments.
E. coli counts in raw sewage are typically in excess of one million organisms per 100ml, counts of 1 - 10 are common in pristine (unpolluted) surface waters. Polluted water can contain counts anywhere in the range of 10 - 1 000 000 organisms per 100ml depending on the degree on faecal contamination.
Health effects - E. coli or faecal coliforms are indicators of the presence of faecal pollution in water and, as such, give an indication of the possible presence of disease-causing microorganisms such as bacteria, viruses or parasites which may give rise to gastro-intestinal diseases. Such diseases are typically characterised by diarrhoea and sometimes by fever and other secondary complications. Dehydration from diarrhoea may be life threatening, particularly in infants, the elderly and the immune-compromised.
pH is a logarithmic expression of the hydrogen ion concentration in water and reflects the degree of acidity (pH less than 7) or alkalinity (pH greater than 7) of the water. In layman's language, pH indicates whether the water is sour (pH<7) or soapy (pH> 7) to the taste. The pH of most unpolluted water sources lies in the range 6.5 - 8.5.
Health effects - These may be direct or indirect. The direct effects are the consequence of the irritation or burning of mucous membranes by extreme pH. The indirect effects are a consequence of the health effects of corrosion products formed during cooking.
Turbidity, defined scientifically as the light-scattering ability of water, is a measure of the cloudiness or muddiness of water. Crystal clear water has very low turbidity, whereas progressive degrees of cloudiness raise the turbidity. Turbidity is caused by the presence of suspended solid matter. The solid matter usually consists of a mixture of inorganic matter, such as clay particles, and organic matter, which again usually consists of both detritus and living organisms.
Health effects - Turbidity does not of itself have direct health effects. However, it is one of the indicators of microbiological water quality. Depending on the nature of the origin of the suspended matter causing the turbidity, there may be associated health effects. Suspended clay particles, often a major contributor to turbidity in surface waters, provide large surfaces for colonisation by bacteria and other micro-organisms.
Three R scripts extract the data from the Department of Water and Sanitation database and generate the tables, graphs and maps. The source code is available here (note that these may not be the latest versions of the scripts):
Last updated 2015-07-06 15:22