The natural and artificial lakes of the Zambezi basin and its rivers, streams and wetlands, make it one of the richest catchment basins in the SADC region in as far as water resources are concerned. The water resources of the basin are used for a multiple of functions including navigation, tourism, hydropower generation, industry, agriculture, environmental and domestic use and others. However, climatic and other conditions determine the availability of water both in space and over time.

Water plays an important role in our everyday lives. The most basic uses for water include domestic uses such as drinking, cooking and washing. Water is also used in large volumes in industry, agriculture and commerce. All aquatic and marine life depends on the availability of clean water for their basic survival needs.

Under conditions of drought, water will become scarce and its social as well as economic value may be seen to rise. Conversely, in times of floods, the value of water more or less declines as it is seen more of a hazard than a life-supporting resource. It is worth noting that the value of water can be linked to the purpose for which it is intended to be used. For instance purified water is valuable for domestic consumption and need not be used for irrigation while recycled water is useful for cooling in industry and cannot be used for drinking. Thus the quality of water determines the amount that can be said to be available for a particular purpose.

The waters of the Zambezi basin are of various qualities, ranging from the almost pure water from the springs, the heavily polluted water from industrial complexes to seawater, which is salty. The quality of the water is influenced by its immediate environment, such as the air, the soil or, in general, its storage medium. Soils of various types have different chemical properties and water stored between the pores of soil will adsorb some minerals to change its chemical properties. For example, in soils that have high content of sulphur, the water will smell like rotten egg. This is common with some hot springs for example.

Similarly, when water mixes with gases emitted from industry, such as oxides of nitrogen and sulphur, the resultant precipitation is acidic to the level that it can destroy crops or vegetation. In homes, water may be polluted through the storage medium that is used such as buckets or tanks. Poor sanitary systems also have a stake in water pollution.

Water quality may be defined as the degree of usefulness of water for a particular purpose. This definition takes into account the fact that even when water is polluted say with sewage, depending on the level of the contaminant, the water can be used for other purposes such as agriculture but is not suitable for use in homes. Thus the quality of water is a measure of the substances contained in it in respect to what the water is intended to be used for.

Water in its natural form in rivers and springs has a quality suitable for sustaining aquatic life such as fish, but substances may be introduced through human activities such as from industries and agriculture, which deteriorate the quality of water. This is called water pollution. Water pollution takes many forms and often has negative effects on human health.

The Zambezi Basin experiences pollution of various forms directly influenced by the activities dominating in the area. Pollution associated with human settlements includes that from mining establishments, industrial complexes especially involved in manufacturing, agriculture through chemicals such as fertilisers, herbicides, pesticides and others, solid waste through pit latrines that contaminates groundwater and also sewage to river, streams and lakes. The environmental impact of pollution is most felt downstream of large settlements such as cities and towns.

Water is found in all three states of matter: gaseous, liquid and solid form. All the time water is changing from one form onto another depending on the energy levels available within its immediate environment. The seas and oceans contain about 94 percent of all water on earth with groundwater accounting for four percent and glaciers and ice caps have about two percent. It is noteworthy that when considering freshwater resources only, the total volume contained in rivers and lakes is negligible.

The movement of water from the gaseous to the liquid and solid states or even in the reverse order, is termed the hydrological cycle. While in motion, and in the gaseous form, water will be in contact with other gases in the atmosphere. Similarly, in its liquid and solid states, it is in touch with minerals, chemicals and other substances that eventually change its original chemical composition. The chemical and physical properties of water are influenced in general by the climate, geology, and human activities in an area. Areas with more rainfall, and depending on the soil types, drain more of both dissolved and suspended matter. Water with high loads of suspended solids has high turbidity levels, that is, looks murky and is not desirable for domestic uses. Mining areas such as the Copperbelt in Zambia, the Maamba (Zambia) and Hwange (Zimbabwe) coal fields and numerous other ore deposits in the basin are associated with pollution of both surface and groundwater.

Flowing water picks up material and chemicals on its way to lakes and the sea. For groundwater, levels of contamination will depend on the age of the water. Water will in some instances have perched above a non-porous medium for decades or even centuries and in this condition will have absorbed a large quantity of minerals associated with its immediate environment. Thus the water may be smelly, will have become salty and unsuitable for many purposes.

In other cases, chemicals can be introduced into natural waterways through human activities such as from industry, agriculture, domestic sewerage, and through poor management of natural resources. Most chemicals are hazardous to human and aquatic life if found in large quantities. Guidelines and standards for water quality are put in place and enforced to ensure that water supplied for the various needs conform to those standards. The commonest guidelines in use the world over are those developed by the World Health Organisation (WHO). Water quality standards and guidelines are a set of limits or levels of chemical and biological contaminants permissible in water. Individual countries adopted WHO guidelines, or set their own which are based on the WHO guidelines. The commonest standards and guidelines in the Zambezi Basin are the WHO standards which are often used in comparison to national standards.

Water pollution may originate from definite single sources, called point sources, such as mine dumps, oil spills or pit latrines in the case of groundwater and from sources that can not be easily located called diffuse sources or non-point sources, such as from agricultural land where contaminants are carried away by runoff.

Biological properties of water involve the amount of living micro-organisms found it. Water in its natural state contains plant and animal micro-organisms such as bacteria, protozoa and algae. Again, it is important that water contains these micro-organisms only in absolute minimum quantities. Water for domestic purposes, for example, need not contain bacteria such as faecal coliform at all, as these are hazardous to health. The quantity of living organisms permissible in water for various uses has to be regulated by use of control guidelines such as the WHO guidelines. Fishing communities such as those along Lake Malawi and Lake Kariba have problems with disposing of their sewerage. Sewerage directly discharged into waterways introduce large volumes of unwanted microbiological life to the system.

For hydrology, variables such as river discharge (volume of water passing a given section of the river per second), and water level can be measured. The rate of flow of a river is used to determine the ability of the river to carry substances, especially pollutants, from one point to the other. With accurate knowledge of river flows, for example, it can be known how long it would take for a pollutant accidentally discharged upstream to reach points downstream, and allow for corrective measures. The discharge is important in that once the concentration of a pollutant is known, the total amount of the pollutant (called load) can be calculated. Water levels are important as they influence other variables such as flow rate. Ground water levels are particularly important measurements in rural and all other areas where people rely on borehole water. We can tell the quality of our water by performing laboratory chemical and/or physical tests to water samples. The Zambezi Basin has varying climatic conditions, but an outstanding feature of the climate is the marked difference between summer (wet) and winter (dry) seasons. The quality of the water in the basin therefore varies with the seasons. It is sad that large economic activities such as mining seldom take note of this.

Water temperature, taste, turbidity, hardness, and smell are some of the basic parameters that can be measured. These parameters for water in natural waterways depend on climate and on geology. Water discharged from industrial works may have higher temperature, and it is therefore important that it be cooled before allowing its flow into rivers and lakes. Plant and animal aquatic life can not do well in hot water, as oxygen levels for respiration and metabolism can be compromised.

Water is generally naturally clear, and departure from this clarity depicts the levels of contaminant present in the water. In particular, the wet season is characterised by dirty (murky) water because of runoff after heavy rains. Odour or smell in water is a result of decaying organic materials or solutions, presence of micro-organisms, or the presence of human wastes. Smelling water suggests that some undesirable elements are in the water but tests are necessary before one can say if these elements are harmful or not. Water may contain small particles of matter (called suspended matter) and dissolved chemicals (called dissolved solids). These, if not desired, can be removed by filtering and evaporating respectively.

Water contains chemicals in various states and concentrations. These may be measured separately, indirectly using methods such as conductivity. Conductivity refers to the ability of the water to conduct electricity that is, its ability to allow electricity to flow through it. While pure water is a poor conductor of electricity, polluted water may contain chemicals that may ‘encourage’ it to conduct electricity better. Conductivity of water is important in that it reflects the amount of dissolved salts (free ions) in the water.

Water in its purel form is neutral, that is, it is neither acidic nor alkaline, and has a pH value of 7. The pH scale measures the acid balance of water. It ranges from zero to 14, with zero as pure acid, seven as neutral and 14 as pure alkaline. The pH of a water sample may vary with time depending on biotic life present, or its chemical composition.

Hardness in water is caused by the presence of magnesium and calcium salts. When hard water is boiled, these salts coagulate and precipitate, and if the water is allowed to evaporate, the precipitate remains in the container.

Oxygen is important in water for aquatic life to ‘breathe’ and for photosynthesis. It is important for almost all natural processes occurring in the water. In general, the more dissolved oxygen there is in water the better, but pollution, high temperature, salinity and biological activity can drastically reduce oxygen amounts. Nitrogen is found naturally and accounts for nearly 80 percent of the gas in the atmosphere. It is important for living organisms as an important constituent of proteins and genetic material. A common source of nitrogen compounds in water is run off from agricultural fields in the form of fertilisers. Nitrogen compounds in water usually take the form of nitrates, nitrites, ammonia and nitrogen. High levels of ammonia indicate organic pollution usually from domestic sewerage, industry or agriculture.

Another common component of water is sulphur and its compounds. In industrialised areas, sulphur is released to the atmosphere as a dioxide, and when it combines with rainwater, it forms an acid (commonly called acid rain) that is corrosive. Acid rain is common in highly industrialised areas. Luckily for the Zambezi Basin, it still enjoys very little to no acid rain incidences.

Eutrophication, the process where water becomes rich in compounds causing an excessive growth of plants such as algae has general negative effects on other life forms that live in water because dissolved oxygen is used up. This problem is persistent in agricultural lands where fertilisers leach into waterways, and in areas where industrial effluent rich in nitrogen and sulphur compounds enter water bodies.

Most metals are found in water as trace elements. The commonest include iron, magnesium, copper and zinc. Metals such as aluminium (especially their sulphates) are believed to cause cancer, while heavy metals such as lead, mercury and manganese are toxic. Organic compounds are a set of compounds centred on carbon, the element commonest in living tissues. The most common organic compounds in water include oils, agro-chemicals especially pesticides, polychlorinated biphenyl (PCBs) and human and animal waste. Many organic compounds enter water bodies as a result of human activities and because they have varying chemical and physical properties, their effects are varying. Pesticides such as DDT were once used rampantly and accumulated in inland water bodies- the main reason for their ban or controlled use.

In general, water from natural waterways carries two types of micro-organisms: bacteria/fungi/protozoa (which form a class of single celled organisms), and algae (which form a class of organisms that can photosynthesise i.e. use light to make food). Water contaminated with micro-organisms can be toxic, or cause diseases depending on their nature. Water pollution by such organisms occurs especially when human excreta are allowed into the water. Diseases such as dysentery, cholera and typhoid are spread this way, and are thus called waterborne. Common bacterial pathogens (such as Salmonella, Shigella, and Escherichia coli.) are responsible for typhoid, paratyphoid, gastro-enteritis, and food poisoning, and can be passed into the water by an apparently healthy person, and further be spread by birds and animals.

Bacteria passed out from the stomach are called coliforms, and are common in running water from populated settlements. In an effort to safeguard human health, strict guidelines on coliforms in drinking and wastewater were suggested, and some coliforms such as faecal coliforms have to be totally absent in water for domestic purposes. A common problem with the Zambezi Basin countries, like all other developing countries, is access to safe water for domestic consumption. Outbreaks of waterborne diseases such as cholera and typhoid are common especially in rural areas. The urban situation is equally bad especially in the municipalities, as there is apparently lack of sufficient funding to institute effective water treatment and quality monitoring.

Water remains an essential element for human survival, development and social and environmental functions and its quality has to be maintained. The time we hold a glass or carry a bucket of water, or when we simply see water wherever it may be, we need to consider the many components that it may contain, how best the water can be used and how important it is, for people and the environment.