Osmosis is a type of diffusion - the diffusion of water across a semipermeable membrane.  Water is small enough to cross the cell membrane without a carrier; since the movement is along the concentration gradient ( [G] -->[L] ), no additional energy input is necessary.  Although carrier molecules are required to move materials across the membrane by facilitated transport (the molecules moved are large, water soluble molecules), an additional input of energy is not necessary since the movement is along the concentration gradient.  Only active transport requires both carrier molecules and energy.