Meaning: Flat leaves stayed on the surface of the water.
Choice of Words: Lily pads are flat, round leaves that float on water. Floated means they stayed on the surface of the water.
Meaning: This sentence also means that the lily pads were floating on the surface of the water, but it uses different words to describe it.
Choice of Words: Rested means to lie or sit in a relaxed way. Water's surface means the top of the water.
Meaning: This sentence means that the lily pads were floating on the surface of the water because they are buoyant.
Choice of Words: Buoyant means able to float on water. Were is a verb that means to exist or to be in a particular state.