Drinking water quality guidelines are often interpreted by the non-expert as make or break cut-off values below which drinking water is absolutely safe, and above which it is totally unacceptable. In reality there is no such knifelike cut-off limit, and there is a large grey area between safe water and undrinkable water. The uncertainty of the boundaries of the grey area for each constituent presents a serious problem, both in the creation of sound drinking water quality guidelines or standards, and in the problem of how to interpret the risk to human health when guideline values are exceeded. In this paper this problem is discussed using the case of arsenic, where the definition of the boundaries of the grey area is particularly uncertain.

Fixed station sampling is the conventional method used to obtain data on the median water quality of reservoirs. A major source of uncertainty associated with this technique is that water quality at the fixed stations may not be representative of the ambient water quality in the reservoir at the time of sampling. This problem is particularly relevant for water quality variables such as chlorophyll, which have a markedly patchy spatial distribution. The use of Landsat reflectance data to estimate median chlorophyll concentrations in Roodeplaat Dam was investigated. A linear polynomial regression model for estimating chlorophyll concentrations from Landsat reflectance data, was firstly calibrated with chlorophyll concentration data obtained by sampling seven fixed stations on the reservoir at the time of the satellite overflight to produce an individual calibration. Secondly, the model was calibrated with a pooled set of sampled data obtained from five separate overflights, to obtain a generalised calibration.It was found that median chlorophyll concentrations determined from Landsat-derived data were similar to median chlorophyll concentrations estimated from fixed station data. However, the range of chlorophyll concentrations in the reservoir estimated from Landsat data was considerably larger than that estimated from fixed station data. Landsat derived estimates of chlorophyll concentrations have the added advantage of providing information on the spatial distribution of chlorophyll in the reservoir.

The Department of Water Affairs and Forestry (DWAF) has carried out a number of case studies on the radiological quality for the water resources near gold mining activities in South Africa. Elevated levels of radioactivity were found in some areas. It thus became important to establish a national monitoring programme that will report on the radiological quality of South Africa's water resources in order to comply with the water resource quality monitoring requirements of the National Water Act (Act 36 of 1998). The purpose of the National Radioactivity Monitoring Programme (NRMP) is to establish the status of, and trends in, radioactivity levels in South African water resources and to report on their radiological quality on a regular basis. This paper discusses issues and decisions taken with regard to the design of the NRMP. A screening method, using alpha/beta activity is proposed to estimate total radioactivity in surface water resources. Where elevated levels of radioactivity have been identified, an element specific analysis will follow. A biweekly sampling frequency has been recommended. Sampling site selection is catchment based and includes sites in high-risk areas. Where possible, use will be made of existing water quality and flow monitoring sites.