Nalco Water, an Ecolab Company, is an American Naperville, Illinois-based supplier of water, energy and air improvement solutions and services for industrial and institutional markets, owned by Ecolab. The company sells various products and services designed to reduce energy, water and other natural resource consumption, enhance air quality, minimize environmental releases and improve productivity and end products.

The company was founded in 1928 as the National Aluminate Corporation, formed from the merger of Chicago Chemical Company and the Aluminum Sales Corporation. By a series of mergers and acquisition, its name was changed to Nalco Chemical Company (1959 – 1999); then Ondeo Nalco Company (1999 – 2004); and in 2004 to Nalco Holding Company. It became a subsidiary of Ecolab Inc. in December 2011 after the completion of the US$5.4 billion acquisition by Ecolab.

Ondeo Nalco has partnered with 2ML Consulting to improve utility operational efficiencies and provide sustainable services to their customers.