Resistivity depth using several types of electrode configuration were made over water wells in an alluvial interior valley of Jamaica, the Queen of Spain's Valley. Results suggest that the yield is a linear function of the resistivity of the water-bearing strata. It is concluded that resistivity surveys can be of material assistance in a water-supply drilling program in the area. Interpretation by multilayer curve-matching procedures gives more realistic results than analysis by classical two-layer master curves used in conjunction with Hummel's rule; also the Wenner array gives a better resolution of small resistivity contrasts than the operationally more versatile Cooper array. Helmholtz' reciprocity theorem of electrical conduction holds also for rock media.