Abstract
Pseudomonas species were isolated from drinking water tanks at Al-Hofuf city from Al-hasa- providence ofthe eastern region of the Kingdom of Saudi Arabia. Water from the drinking water tanks was analyzed to determine the prevailing microorganisms. Fifteen (15) water samples were screened on SS agar medium; only four (4) water samples were highly infected with members of familyentrobactereaceae. Identification of the bacterial isolates was done using API-20E kit provided from biomeurexin addition to sequencing 16srRNA. The evolutionary history wasinferred using the Neighbor-Joining Method based on the16s rRNA. Identification of bacteria isolated on SSagar plates indicated Pseudomonas species as the principal bacterial species involved; three bacterial species belongs to genusPseudomonas; these are; Pseudomonas mendocina, Pseudomonas alcaligenes, Pseudomonas sp. and one species ofDelftiatsuruhatensiswere found to be the major contaminants of drinking water tanks at studied area and provide a possible health risk.