and list the problems, and to identify priority areas within which more detailed investigations should be carried out.
a) Categorisation of water quality problems
Identified water quality problems may fall into different categories requiring application of different management tools and interventions for optimal resolution of the problems.
For example, if a problem exists at the basin scale it might be necessary to consider imposing general effluent standards, regulations or other relevant measures. In contrast, if the problem is limited to a small geographic region it might only be necessary to consider local regulation or intervention to settle a dispute.
It may also be useful to categorise water quality problems as either “impact issues” or “user-requirement issues”. Impact issues are those that result in environmental damage or impact for example on the health of the community downstream. User-requirement issues are those which derive from an inadequate matching of user-specified water quality requirements (demand) and the actual quality of the available resources (supply). (Box 6.3).
b) Prioritisation of action
Even if all existing and potential water quality problems could be identified it is not feasible to solve them all at once and priorities have to be established.
The process of assigning priority to water quality problems requires a management decision and some important aspects to be considered include:
• economic impact • duration of impact
• human health impact • type of pollution
• impact on ecosystem • geographical extent of impact
As an example, the uncontrolled growth of water hyacinth in a water body may lead to a deterioration in water quality from oxygen depletion, may also hamper navigation, affect fishing and increase the cost of water supply treatment with considerable economic consequences. Thus, based on this simple analysis, combating the proliferation of water hyacinth should be given a higher priority than might be indicated by purely environmental considerations.