What marking must be on pipes or tubes that are not capable of handling hot water?

The marking "For Cold Water Use Only" is essential for pipes or tubes that are not designed to handle hot water, as it provides clear and specific guidance to the users and installers regarding the intended application of the piping or tubing. These markings are crucial for ensuring safety and preventing accidents that could result from the misuse of materials not capable of withstanding high temperatures.

When users see this marking, it immediately informs them that the product must be limited to cold water applications, protecting both the integrity of the piping and the safety of the system in which it is installed. Additionally, using a pipe meant for cold water in a hot water application could lead to failure due to deformation, leaks, or even bursts, which can have serious safety implications.

Other options do not provide the clear and direct instruction that is necessary for ensuring proper use. For instance, "Caution: Hot Water Inside" could be misleading if the material is not meant to handle hot water, and “Use with Caution” is vague and does not specify the parameters of usage. "Temperature Sensitive Material" does indicate some special consideration for temperature but lacks the definitive guidance that "For Cold Water Use Only" provides.