Water seems plentiful, covering about three-quarters of the earth's surface, but most of it is salt water in oceans or frozen in polar regions.
(Water; covering; about three-quarters of the earth's surface) (most of it; is; salt water in oceans or frozen in polar regions) (most of it; frozen; in polar regions)
Water most of it most of it
covering is frozen
about three-quarters of the earth's surface
salt water in oceans or frozen in polar regions
in polar regions