The three habitats examined (ground water, man-made containers and tree holes), had similar levels of sodium, chloride, and conductivity. Water hardness was less in tree holes than containers and ground water. The pH of tree holes was acidic while containers and ground water were basic. Potassium concentration was highest in tree holes followed by containers and ground water. Aedes triseriatus and Orthopodomyia signifera were collected in tree holes having higher potassium levels than Anopheles barberi. Seven species, found in containers and ground water, could be divided into two groups on the basis of potassium level. Anopheles punctipennis, Culiseta inornata, Culex tarsalis and Cx. pipiens were found at high potassium levels while Cx. restuans, Cx. salinarius and Cx. territans were found in habitats containing lower potassium levels.