17.4 Indicators of water pollution
The physical, chemical and biological characteristics of water are changed when the water is contaminated with different pollutants. Water is colourless, odourless and tasteless, as you know, but when it is polluted with physical and chemical pollutants the water may have colour, odour and taste.
If water is completely clear and has no colour or odour, is it safe to drink?
Not necessarily, because it may contain microorganisms or dissolved chemicals that cannot be seen.
To know whether water is polluted with specific bacterial contaminants, samples should be taken and sent to a laboratory for analysis. As noted in Study Session 16, E.coli is the standard indicator organism for faecal contamination of water and for the possible presence of faecal pathogens. For water intended for drinking, the World Health Organization (WHO) recommends that E.coli must not be detectable in any 100 ml sample. In most developing countries like Ethiopia the priority is to get from ‘bad’ quality (more than 1,000 faecal coliforms per 100 ml) to ‘moderate’ quality (less than 10 faecal coliforms per 100 ml). ‘Good’ quality is classed as zero faecal coliforms per 100ml.