As of 1985, Calgon Carbon was operating as a subsidiary of Merck and Co. However, that year Calgon Carbon's management purchased their own company from Merck and Co in a leveraged buyout. Calgon Carbon made an initial public offering of common stock in 1987. Around 1990 the company came out with an "advanced UV oxidation process to remediate contaminated groundwater," and three years later Thames Water, a large utilities company in the United Kingdom, granted Calgon Carbon exclusive rights to market technology that cleaned organic compounds such as pesticides out of drinking water.