There are generally two versions of the answer to this question. The first is the more general about 70% of Earth is water while about 30% is land (US Geological Society). The second is the more specific 71% of Earth is water while 29% is land. Both will serve, depending upon your need and aim. The interesting thing is that the percentage of water on Earth does not include only the obvious sources of water, like oceans and lakes, but less obvious sources as well.
The totality of Earth's water is comprised of water in the oceans, water in the air, water in frozen icecaps and glaciers, water in underground aquifers, and water in lakes, rivers and ponds. The largest portion of all this water is found in oceans and seas--being saline water--which hold between 96.5% and 97.5% of all water. That leaves between 3.5% and 2.5% distributed between all Earth's freshwater sources, including water vapor in the air and water in occupants of Earth (US Geological Society). Earth's hydrologic cycle, the movement of water from Earth to air to Earth's occupants, keeps the water circulating and going through various hydrologic phases, liquid, vapor and frozen forms such as snow and ice.
If the water above ground, saline and freshwater, on Earth is measured by volume, the total volume would cover about 1,064 miles in diameter and more than 335,000,000 cubic miles. The third greatest source of water, after (1) oceans and seas and (2) icecaps and glaciers, is ground water, or aquifers. The volume of aquifer water is about 5,614,000 cubic miles. Compare this to the second greatest (icecaps, glaciers) at about 5,773,000 cubic miles. These volumes are surprisingly close while saline oceanic water bears no comparison at all, with a volume of 321,000,000 cubic miles. About 30%, then, of Earth's total freshwater is ground aquifer water or about one-third the amount frozen is icecaps and glaciers. Rivers constitute the smallest volume of Earth's water--aside from biological water in Earth's occupants--with a volume of 509 cubic miles.
It is interesting to note that of Earth's freshwater sources, about 69% is in icecaps and glaciers (NOAA). This establishes a significant link between ocean levels and ice sheets as they calf, break off, or in other ways melt in mountain glaciers, Antarctica, Greenland and other significant ice zones. Since oceans cover so significant an expanse of Earth's surface, it is not surprising that they play a significant role in global climate stability and in global climate change. Because of the oceans' importance, more and more studies are revealing more and more interactions and connections. For instance, while warming temperatures from greenhouse gases cause greater ocean cloud cover, counteracting some of the rise in Earth temperature, the warming is also raising sea levels and making ocean waters more acidic affecting saltwater flora and sea creatures. Findings published in Nature in January 2014 show that warming currents in the North Atlantic adversely affect (1) "sea-ice redistribution" (i.e., shifting positions of large bodies of sea-ice) in Antarctica, (2) melting ice in the southern icecap of Antarctica, (3) a warming climate with (4) increased ice melt in Antarctica. Greenland and Antarctica together hold about 99% of Earth's freshwater ice, which is undergoing significant changes in location and water phase (from frozen to liquid and vapor).