What is an approved adaptor to connect copper to PVC piping?

A mechanical joint is the correct choice for connecting copper to PVC piping. This type of connection is specifically designed to accommodate different materials, like copper and PVC, without the need for direct bonding or welding, which can result in issues due to different thermal expansions and contractions of the materials.

Mechanical joints typically use a flange or a coupling that allows for a secure and leak-proof connection while maintaining the integrity of both materials. This method is advantageous because it permits easy disassembly if necessary and does not compromise either pipe's properties.

In contrast, solder joints require the use of heat to join two metal pieces together, which is not applicable for connecting a plastic material like PVC directly to copper. Threaded joints are primarily used between fittings rather than directly connecting dissimilar materials. Compression joints also have limitations when it comes to ensuring a robust connection between differing materials like copper and PVC. Therefore, the mechanical joint stands out as the most approved and effective method for this particular application.