One of a series of general interest publications on science topics, this booklet provides those interested in the composition of sea water with a non-technical introduction to the subject. Focusing on the saltiness of the sea, separate sections examine the origins of the sea, sources of the salts, why the sea is not fresh, the complexity of sea water, salinity and its variability, and how sea life affects sea water's composition. The text is accompanied by charts and diagrams illustrating the sources of salts in the sea, principal constituents of seawater, and the chemical differences between sea water and river water. (LH)