The classic material for water boxes has always been:

The classic material for water boxes has indeed been cast iron. This material is favored due to its excellent resistance to corrosion, durability, and strength, which are essential qualities for components that regularly come into contact with water, especially in boiler systems and heat exchangers where water can be corrosive. Cast iron can withstand high temperatures and pressures, making it suitable for handling various operational conditions in power engineering.

Additionally, cast iron is known for its ability to absorb vibrations, which is beneficial in mechanical applications to reduce wear and tear on other components. This combination of characteristics has made cast iron a longstanding choice in the engineering of water boxes, where reliability and longevity are critical factors in performance and maintenance.