A solar collector device for the warming up of water, comprising a flat cylinder-shaped absorber element through which the water flows and made of temperature resistent black polymeric film material, on the sunside a cover element of at least one transparent polymeric film and on the shadowside an insulation panel. In the black polymeric film of the absorber element spectral-selective absorption pigment is embedded and an inner film is used with a high impermeability for water and water vapor, which latter film is laminated with the black outer film to one integrated film. The absorber element is executed for a great length of many tens of meters. A water header having a weir device is provided at the outlet side of the absorber element and, below said header, a water collecting tank. The weir device has such a height with respect to the absorber element, that, in combination with the correct dimensioning of the water inlet and outlet openings, the absorber element operates with a water layer height of a few centimeters c.q. with a water velocity of a few centimeters per second.