What type of piping should not be used for a beverage system according to plumbing guidelines?

The correct choice identifies an important safety and health consideration regarding beverage systems. Plastic piping is often not recommended for beverage systems due to concerns about leaching chemicals into the beverages. Many plastics can release harmful substances when in contact with liquids, particularly those that are hot or acidic, which is common in beverage applications. This can compromise the quality of the beverage and potentially affect user health.

On the other hand, metal piping is typically approved and widely used in beverage systems due to its durability and resistance to leaching. Wood piping is largely obsolete in modern plumbing but has historical significance, while composite piping can be designed specifically for certain applications and may be acceptable depending on the materials used. Therefore, the restriction on plastic piping stems primarily from safety concerns associated with material integrity and chemical interaction with the fluids being transported.