Measurements in Bahrain (Doornkamp et al 1980), have shown a strong linear relationship between electrical conductivity and the ionic concentrations of sulphates and chlorides in groundwaters. Indeed, the relationship proved so strong as to imply that electrical conductivity could be used as a surrogate for sulphates and chlorides, and that the two latter could be estimated from the former in field reconnaisance surveys or even site investigations.

This is of critical importance to the construction industry, and to agriculture, in hot arid lands. Concrete is known to deteriorate rapidly in the presence of saline groundwater (Fookes & Collis 1975, 1976; Cooke et al 1982), and any quick estimate of the sulphate and chloride levels is of practical value. Field measurements of electrical conductivity can be made rapidly using a portable electrical conductivity meter, while the laboratory analyses of sulphates and chlorides need care and introduce time delays, particularly for the construction industry, as well as additional costs.

What is not known is whether the results obtained in Bahrain provide a universally applicable relationship. Do the regression equations obtained in Bahrain hold good for all hot arid lands? If so, can they be used as a basis for estimating sulphate and chloride concentrations from simple electrical conductivity measurements without the need to resort to laboratory tests? Some standard texts (e.g. Davis & de Wiest 1966) suggest this could be so.

To test these questions two further analyses have been carried out. The first is for data collected by the Egyptian Groundwater

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