Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.
Classify the following examples of water pollutants using the categories shown in the table below:
| Category of water pollutant | Examples |
| Sediments and suspended solids | |
| Organic matter | |
| Biological pollutants | |
| Plant nutrients | |
| Other chemical pollutants |
The answer is as follows:
| Category of water pollutant | Examples |
| Sediments and suspended solids | sand, silt |
| Organic matter | faecal matter |
| Biological pollutants | bacteria, protozoa, intestinal worms |
| Plant nutrients | nitrates, phosphates |
| Other chemical pollutants | copper, lead, insecticides |
The following are pollution sources. Give two specific pollutants for each source.
A residential area: ………………………………………………
A metal plating plant: ………………………………………………
Agricultural activities: ………………………………………………
An uncontrolled landfill site: ………………………………………………
Urban surface water run-off: ………………………………………………
There are several possibilities, listed below.
| A residential area: | human excreta, wastewater containing dissolved and suspended organic matter, suspended inorganic matter, pathogenic micro-organisms |
| A metal plating plant: | cyanides, heavy metals |
| Agricultural activities: | nitrates, phosphates, pesticides |
| An uncontrolled landfill site: | leachate containing dissolved organic matter, inorganic components and heavy metals |
| Urban surface water run-off: | sediment, metals, hydrocarbons, rubber, detergents, litter |
Read Case Study 4.1 and then answer the questions that follow.
Mekanisa is a place in the southern part of Addis Ababa where urban agriculture is practised. A group of farmers grow different varieties of vegetables and sell them to people in the city. The farmers use water from the nearest river (the River Kera) for irrigation. They mostly grow leafy vegetables, with two harvests a year.
The Kera River originates a few kilometres from Mekanisa and passes through residential, commercial and industrial areas before reaching Mekanisa. Along its way, human excreta and industrial wastes are indiscriminately discharged into the river. One of the prominent polluters of the river is the city’s biggest slaughterhouse, located at the side of the river. Untreated wastewater from the slaughterhouse is discharged into the river giving a blue-black colour to the water. Farmers like this type of water for irrigation as it helps their crops grow.
One of the authors of this Module undertook research assessing the level of pollution of the river water. The results are shown in Table 4.2.
| Parameters | FAO* Guideline Concentrations for components in irrigation water (Pescod, 1992) | River water |
| Faecal coliforms | <1000 per 100 ml | >2500 per 100 ml |
| Copper | 0.2 mg l-1 | 25.5 mg l–1 |
| Zinc | 2.0 mg l-1 | 56.3 mg l–1 |
| Iron | 5.0 mg l-1 | 71.0 mg l–1 |
| Lead | 5.0 mg l-1 | 19.0 mg l–1 |
| Manganese | 0.2 mg l-1 | 37.0 mg l–1 |
| *FAO is the Food and Agriculture Organization of the United Nations. | ||
Which of the following statements is false? In each case, explain why it is incorrect.
1 is false. Latrines should be below a water source on sloping ground otherwise seepage from the pit could flow down into the water source.
2 is false. The protection measures are correct but the cover should have a lock.
5 is false. Water use is relevant to several different ministries, all of which should be consulted when legislation is being prepared.