Water and Water Pollution

Author: Hanlie Hattingh, Anthony Turton, Christine Colvin, Marius Claassen & Peter Ashton; and statistics provided by Peter Ashton & Linda Godfrey – CSIR

( Article Type: Overview )

Water is a fugitive natural resource, changing between solid, liquid and gaseous forms that are linked via the hydrological cycle (see Figure 1) that move freely in time and space. Planet Earth is the only known place where water occurs in liquid form. Water is literally the essence of life, acting as a solvent, diluting and dispersing waste products, providing essential ecological services, and underpinning all economic activities.

Water quantity

The core problems facing South African water resource managers are shaped by two key climatic characteristics.

First, the generally low and variable levels of rainfall across most of the country control the amount of water available (see Figure 2). South Africa receives approximately 500 millimetres of rainfall each year – far less than the global average of 860 millimetres.

Second, high air temperatures and low humidity levels mean that most rainfall is lost via evaporation and less than 10% of the rainfall is converted into usable groundwater or river flows. The flows in South African rivers are extremely variable, with large fluctuations between seasons and between years. This variability has shaped the character of southern African aquatic ecosystems.

Availability

Most of South Africa’s rain falls on the eastern, southern and south western coastal and adjacent areas. Approximately 60% of the annual rainfall falls on only 20% of the country’s land surface. The highly seasonal rainfall patterns and steep slopes in the higher rainfall areas pose significant challenges to managing water supplies. Unlike some of South Africa’s other natural resources (gold, coal, etc.), water’s mobility and its relative scarcity means that it has the potential to limit future economic growth and thereby influence political stability.

• too little (drought)
• too much (floods)
• too dirty (pollution)
• wrong time (storage)
• wrong place (inter-basin transfers).

Figure 2. Map of southern Africa showing the distribution of mean annual rainfall isohyets and positions of large dams (with a capacity greater than 2 million cubic metres and/or a dam wall that is higher than 15 metres)

Five Key Water Issues 

The climatic characteristics of South Africa mean that our water resource managers must deal with all five of these categories of water issues. Specific solutions are needed for each issue.

Issue 1: Too Little (Drought)

 Traditionally, South African water resource managers focused on coping with water shortages and droughts. Large engineering projects were designed to capture and contain water to provide the highest possible assurance of supply to the country’s growing population; South Africa is now one of the top 20 countries in the world to have built the highest number of large dams. While this infrastructure has improved the assurance of supply, it also had unintended consequences; for example, improved control over river flows has adverse consequences for aquatic ecosystems that are adapted to high levels of flow variability.

Issue 2: Too Much (Floods)

Flooding poses numerous threats as the infrastructure and operating rules needed to manage floods are different to those needed for drought management. Dams constructed for water supply are usually kept as full as possible. With the arrival of a flood, some water has to be released so that the floodwaters can be retained and released slowly without causing damage downstream. Reliable weather forecasting allows dam managers to release water before a flood event and creating sufficient space for the incoming floods. However, the variable and unpredictable nature of the South African climate makes this difficult to achieve.

Issue 3: Too Dirty (Pollution)

Pollution poses several high priority problems because of the relative scarcity of water in South Africa. Pollution has several sources, mostly linked to patterns of land use and the discharge of gaseous, liquid and solid effluents. Domestic and industrial effluents contain potentially toxic compounds and have to be treated before they can be discharged into a watercourse or the ocean. Gaseous emissions from power stations, mines and industries combine with water in the atmosphere to form dilute acids. When this falls to Earth as so-called ‘acid rain’, it can have widespread effects on soils, vegetation and water bodies located far from the original pollution source. Incomplete removal of the phosphate and nitrate in effluent flows from domestic, industrial and agricultural sources, results in nutrient enrichment of downstream watercourses.

Issue 4: Wrong Time (Storage)

Cities such as Cape Town that are located far from reliable supplies of fresh water pose specific water supply problems. The entire economy of the winter rainfall areas in South Africa depends on sufficient storage capacity to last through the dry summer months. This has substantial ecological impacts on local river systems and these unintended consequences have to be managed very carefully. This is also closely related to Issue 5: Wrong Place. Increasingly, the storage naturally held in aquifers, like the sandy aquifers along the coast or fractured hard rock aquifers, is being used to augment supplies to communities that have traditionally relied on dams.

Issue 5: Wrong Place (Inter-Basin Transfers)

A key element of South Africa’s economic development has been the large-scale inter-basin transfers of water. The most notable of these schemes are the Orange River Project that provides water for the economic areas around Port Elizabeth; the Palmiet-Breede Pumped Storage Scheme that supplies Cape Town; and the combined Lesotho Highlands Water Project and the Thukela-Vaal transfers that sustain Greater Johannesburg. Importantly, the four most economically developed countries in the SADC region (South Africa, Namibia, Botswana and Zimbabwe) are all highly water-stressed and their future economic stability will depend on inter-basin transfers of water. Schemes under investigation include transfers from the Zambezi and the Congo River basins; all of these have major potential ecological impacts and would be very costly to build.

Water quality

Water quality refers to the state of the water in terms of its purity or level of contamination. Water quality impacts water availability, because the water is often too polluted to be used safely, thereby being technically unavailable even if it is physically present in the landscape.

Water resource quality is defined in the National Water Act (NWA, Act No. 36 of 1998) as the quality of all the aspects of a water resource, including instream flow (quantity, pattern, timing, water level and assurance), water quality (physical, chemical and biological characteristics), in-stream and riparian habitat (character and condition) and aquatic biota (characteristics, condition and distribution).

Water of poor quality is less suited to support socio-economic activities. Industries usually depend on clean water to produce quality products in efficient processes, where poor water quality can lead to scaling of pipes and infrastructure, interference with chemical processes and cause health risks. Poor quality irrigation water can affect crop growth and reduce yields or lead to increased salt loads in soils, which renders them less productive. Poor water quality also reduces options for domestic and recreational use. While human health is mostly affected by microbiological contamination due to inadequate sanitation, excessive algal growth can lead to the production of toxins. Other impacts on human health from poor quality water include carcinogenic substances such as pesticides and solvents that can cause cancer, oestrogenmimicking substances from industrial and domestic waste that leads to the feminisation of males and water-related diseases such as cholera and diarrhoea.

Factors influencing water quality

There are two primary factors influencing water quality. The first relates to the natural environmental conditions that exist, such as the source of the water, the type of rocks and soil through which it passes and the ambient temperature to which it is exposed. For example, water may be unusable due to a high salt concentration or be brackish as a result of the natural rock and soil conditions within the area.

The second primary factor influencing water quality relates to human activities. All human activities impact on water quality in one way or another. Clearing forests, increases the drainage into the rivers, taking with it topsoil, which increases the solids presents in the water. If water drains over agricultural land, pesticides and fertiliser will be deposited in the river systems, leading to a higher concentration of organic substances in the water. Run-off water may also be contaminated with human waste, specifically in areas where proper sanitation facilities are not provided, leading to faecal contamination of the water and a likelihood of diseases being spread. It also leads to algal blooms, and eutrophication. Whilst industries should return their abstracted water to the water resource, the water often contains industrial effluent, which if not cleaned before it is returned, will contaminate the water resource. Run-off and storm water from industrial sites is also usually significantly contaminated.

In addition to the contamination of water resources, water extraction reduces river and stream flow. When water volume and flow in rivers is significantly reduced, the concentration of different substances is increased. The main problems that result include the accumulation of sediments in the water and salination (a high salt concentration in the water – rendering it unusable for human consumption and agricultural purposes).