3.3.1 Water Quality

Water bodies can be fully characterised by the three major components, namely, hydrology, physico-chemistry, and biology. Under each component a large choice of variables can be used to describe the status of water bodies
quantitatively. The factors determining water quality are thus complex, making it difficult to define water quality in simple terms. "Water quality" should, therefore, be considered to mean the overall quality of the aquatic environment (Chapman, 1992). The quality of the aquatic environment shows temporal and spatial variations due to factors internal and external to a water body.

3.3.2 Global Freshwater Quality Issues

Chemical water quality issues have evolved over the years with each stage of industrialisation. In the developed countries, the focus on water quality issues has shifted from faecal, organic pollution and salinisation in the late 19 th century to metal pollution, eutrophication and problems of radioactive wastes in the early to mid 20 th century. During the last thirty years, problems of organic micro-pollutants (pesticide residues) and acid rain have become more important as water quality issues.

3.3.3 State of Water Environment: Water Pollution in Kenya

Water resources in Kenya are increasingly becoming polluted from both point and non-point sources due to agriculture, urbanisation, and industry which contribute to organic, inorganic and aesthetic pollution of water. Ground-water is threatened by intrusion of saline water in the coastal region, leachates from solid waste dumps, and infiltration of fertilizer and pesticide residues. The five principal sources of water pollution in Kenya include,
among others, the categories listed below, (JICA/GOK, 1992).

(a) Agricultural activities which produce sediments and agro-chemical residues (biocides and fertilizers).
(b) Industrial processing of agricultural and forestry products which produce liquid effluents, gaseous emissions and solid wastes.
(c) Industrial manufacturing - heavy metals, acids, dyes, oils.
(d) Domestic/municipal effluents - sewage and garbage.
(e) Sedimentation - soil erosion; and mining which produces tailings and effluents.

Municipalities and industries constitute the largest source of waste water discharges; however, industries discharge an enormous variety of wastes some of which are toxic to human beings and the general environment. Examples of such industrial wastes, which are a critical environmental issue in Kenya include effluents, sludges and solid waste from sugar, coffee pulping and textile factories, leather tanneries, paper-mills and slaughter- houses.

All these wastes impact on water quality and are manifested through:
(i) deterioration of the quality of the aquatic environment, namely, deoxygenation, eutrophication, siltation, habitat modification and toxicity, among others;
(ii) environmental health effects with the occurrence of water-borne diseases, for example, typhoid and cholera, and chemical poisoning in humans and animals;
(iii) aesthetic effects leading to loss of scenic beauty with water becoming unsuitable for recreation;
(iv) high cost of water supply as polluted water is expensive to treat; and,
(v) water rights conflicts due to shortage of water of suitable quality for domestic, industrial and irrigation purposes. In order to protect Kenya's water resources from further degradation, water pollution or effluent discharge standards are necessary.

3.3.4 Water Pollution Control Guidelines/Standards Setting

In practice, standards can be set from either first principles or based on existing guidelines; international or national. For first principles, classification, and prioritisation of pollutants is necessary. Pollutant exposure processes and their ecological effects should be determined. Predicted environmental concentrations (PEC) and predicted no effect concentration (PNEC) for the aquatic environment should be derived. Usually, actual analytical data (baseline data) relevant to the locality or country situation are preferred.

Standards can also be based on existing guidelines such as those of the International Standards Organisation (ISO) or other similar country standards. Baseline data collection is then undertaken to improve or adapt the initial standards to own country situation. Thus, baseline data is important for the setting of standards for water pollution as well as:

(a) forming a basis for zoning; where general or special standards should apply;
(b) assessing the assimilative capacity of various streams;
(c) identifying the water courses which require stringent or less stringent application of standards; and,
(d) formulating rehabilitation and/or conservation measures.