Precipitation that falls on the land either evaporates, flows across the surface, or soaks into the ground. Water moving across the surface is called runoff. Water that moves across the land as a small body of running water is called a stream. A stream drains an area of land known as the stream drainage basin or watershed. The watershed of one stream is separated from the watershed of another by a line called a divide. Water that collects as a small body of standing water is called a pond, and a larger body is called a lake. A reservoir is a natural pond, a natural lake, or a lake or pond created by building a dam for water management or control. The water of streams, ponds, lakes, and reservoirs is collectively called surface water.

Precipitation that soaks into the ground percolates downward until it reaches a zone of saturation. Water from the saturated zone is called groundwater. The amount of water that a material will hold depends on its porosity, and how well the water can move through the material depends on its permeability. The surface of the zone of saturation is called the water table.

The ocean is the single, continuous body of salt water on the surface of the earth. A sea is a smaller part of the ocean with different characteristics. The dissolved materials in seawater are mostly the ions of six substances, but sodium ions and chlorine ions are the most abundant. Salinity is a measure of the mass of salts dissolved in 1,000 grams of seawater.

An ocean wave is a moving disturbance that travels across the surface of the ocean. In its simplest form a wave has a ridge called a crest and a depression called a trough. Waves have a characteristic wave height, wavelength, and wave period. The characteristics of waves made by the wind depend on the wind speed, the time the wind blows, and the fetch. Regular groups of low-profile, long-wavelength waves are called swell. When swell approaches a shore, the wave slows and increases in wave height. This slowing refracts, or bends, the waves so they approach the shore head-on. When the wave height becomes too steep, the top part breaks forward, forming breakers in the surf zone. Water accumulates at the shore from the breakers and returns to the sea as undertow, as longshore currents, or in rip currents.

Earthquakes or undersea landslides produce large, destructive waves called tsunamis. Tsunamis do not have a large wave height at open sea, but they can do tremendous damage when they reach a low coastal area. A tide moving in or out of a narrow bay can produce a wave called a tidal bore.

Ocean currents are streams of water that move through other seawater over large distances. Some ocean currents are density currents, which are caused by differences in water temperature, salinity, or suspended sediments. Each ocean has a great system of moving water called a gyre that is centered in mid-latitudes. Different parts of a gyre are given different names such as the Gulf Stream or the California Current. The ocean floor is made up of the continental shelf, the continental slope, and the ocean basin. The ocean basin has two main parts, the abyssal plain and mountain chains called ridges.