Before delving into the strange science behind freezing water, it’s beneficial to address the common myth that cold water boils faster than hot water. The New York Times tells us that notion is untrue, and may have been constructed as a way to deter people from cooking with hot tap water, which contains more impurities. Additionally, Denver Water explains that hot water can dissolve the contaminants found in your water heater and pipes.
The science behind the reverse phenomenon of freezing water is much less cut and dry.
According to the University of Oregon, water freezes at 32 degrees Fahrenheit and 0 degrees Celsius, so it stands to reason that cold tap water would freeze faster. Cleveland Clinic Health Essentials says that cold tap water is usually around 60 degrees Fahrenheit, which is only a quick jump of around 30 degrees to water’s freezing point. But science is a complicated thing, and in certain circumstances, hot water can actually freeze faster than cold water (via Cosmos Magazine).