The fact that water reaches its maximum density at approximately 4 degrees Celsius is a well-established physical property of water and represents common knowledge that requires no citation.
The claim states a fundamental, well-known physical property of water (maximum density at 4°C), which is a matter of everyday scientific observation and physical definition. Per the instructions, trivial physical facts and common knowledge do not require citations, and the verdict COMMON_KNOWLEDGE should be returned without attaching papers.