The hydrosphere does contain a tremendous amount of water-about 1360 million cubic kilometers (326 million mi3). That is enough water to cover the entire United States to a depth of 145 kilometers (90 mi). Put another way, it is about 171 million gallons of water per person on Earth. So there is a lot of water. The problem is that, as Figure 10-3a indicates, 97.2% is ocean water, which is too salty to drink or grow crops with. Just 2.8% is freshwater.