Abstract: An apparatus for covering a basin for liquids, for instance basins used for purification of waste water. The apparatus according to the invention comprises a covering element, with a regular circumferential shape, so that they can be located adjacent, which covering element floats unto the liquid to be covered. For making the element float a number of floating elements is provided at the lower side of the elements, but these floating elements are not adjacent. Consequently the resulting upward floating force of the floating element keeps the lower side of the covering element on a distance from the surface of the liquid. This distance allows draining or removal of bodies floating on the liquid. Preferably the upper surface of the covering element has the shape of a deepened tray to allow the collection of rain water, so that the elements cannot be blown away.

Abstract: A floating covering on the liquid content of a storage tank. The circumferential edge of the covering has an elastic annular body provided with a gas-tight annular chamber and an annular body of foam material. Pressure control means communicates with the chamber for selectively pressurizing and releasing pressure from the chamber.