Calgon is a brand registered trademark of water softener, and bath and beauty products. The original product consisted of powdered sodium hexametaphosphate (amorphous sodium polyphosphate), which in water would complex with ambient calcium ion and certain other cations, preventing formation of unwanted salts and interference by those cations with the actions of soap or other detergents. Its name was a portmanteau derived from the phrase "calcium gone".[1] Originally promoted for general use in bathing and cleaning, it gave rise to derivative products which have diverged from the original composition. Today, Calgon water softener contains the active ingredients zeolite and polycarboxylate, which are less problematic in wastewater treatment than phosphates.

The Calgon water softener was first introduced to the market in 1933 by Calgon, Inc. of Pittsburgh, Pennsylvania. Calgon, Inc. was acquired by Merck in 1968 and later broken up and sold off. Today, the brand is owned by Reckitt Benckiser for use in Europe as a water softener, and in the United States by Ilex Consumer Products Group as a bath and beauty product.