Which material is NOT allowable for contact use in potable water systems?

In potable water systems, it is essential to use materials that do not corrode or leach harmful substances into the water supply. Galvanized steel is not an allowable material for contact use in potable water systems primarily because it is coated with a layer of zinc to prevent corrosion. Over time, this zinc can corrode and leach into the water, potentially leading to health concerns for consumers.

In contrast, FDA-approved rubber, AISI Type 300 series stainless steel, and glass-lined metal are acceptable for use in potable water systems. These materials are specifically designed or treated to withstand corrosion and are safe for contact with drinking water. For instance, the FDA has established guidelines ensuring that certain rubber materials are safe for use, while the stainless steel types provide a durable, corrosion-resistant option. Glass-lined metal additionally offers a protective layer that prevents leaching and is suitable for maintaining the integrity of potable water. Thus, galvanized steel stands out as unsuitable due to its potential to introduce contaminants.