These improvements are directed to provide said device with two tanks, (1,4), one within the other, and both designed to be water filled (N1) without dousing the inside tank (4). Said tank (4) is top opened (5) and provided with a heating element (7) to achieve water ebulliency. The outside tank (1) has a delivery (2) wherefrom only the evaporated water (Ve) goes out while the engendered foam-water (Vp) is condensed and comes back to the outside tank (1). At the bottom of the inside tank (1) a hole (6) is provided with a section (d) which rate of water inflow (Vi) is equivalent to the evaporated water rate (Ve) plus the foam-water rate (Vp). The outside tank (1) has an inlet (3) to refill water therefrom when level reaches a minimum (N2). Applicable to any water diffusers in aesthetics and medicine.