Complex sentence: In the United States, an average of 1 ppm of fluoride is intentionally added to water supplies for water fluoridation, while the Maximum Contaminant Level (as established by the US Environmental Protection Agency) is 4 ppm.
Split into simpler sentences: In the United States, an average of 1 ppm of fluoride is intentionally added to water supplies for water fluoridation. The Maximum Contaminant Level (as established by the US Environmental Protection Agency) is 4 ppm.