On which size water line should fire hydrants never be placed?

Fire hydrants should never be placed on a 6-inch water line because this size pipe typically does not have sufficient capacity to support the volume of water required for firefighting. A 6-inch line may limit the flow rate, which is critical during an emergency response when large volumes of water are needed rapidly. Fire hydrants are generally installed on larger mains, such as 8-inch or 10-inch lines, which can better accommodate the demand for water flow during a fire. This ensures that firefighters have consistent and adequate water supplies when combating flames, thus improving emergency response effectiveness. Additionally, 4-inch lines are also generally deemed inadequate for fire hydrants due to similar flow capacity issues, but the most common standard dictates avoiding 6-inch lines specifically.