Abstract: A water treating device includes an outer casing, a reverse osmosis tube, a side cap, and an outlet tube. The outer casing includes an outer tube having a first inlet for water and a first outlet, an inner tube mounted inside the outer tube and including a number of holes defined in a periphery of an end thereof, and a water-permeable layer mounted between the inner tube and the outer tube. The reverse osmosis tube is mounted in the inner tube and includes a second inlet for water from the holes of the inner tube and adjacent to the end of the outer tube. The reverse osmosis tube further includes a second outlet for pure water. The side cap is mounted to seal a first end of the outer casing and includes a first electric rod to interconnect the outer tube with a positive power connection and a second electric rod to interconnect the inner tube with a negative power connection.