Where are indirect connections prohibited in a building's plumbing system?

Indirect connections in a building's plumbing system are prohibited in a crawl space primarily due to the potential for contamination of the potable water supply. Crawl spaces can be damp and are often prone to flooding or moisture accumulation, which increases the risk of backflow or cross-connection with wastewater. If an indirect connection is established in such an environment, it can lead to drainage odors, pests, and, most critically, it can compromise the safety of drinking water by allowing contaminants to enter the water supply through the indirect connection.

Other areas, while they may have their own risks, such as a basement, garage, or attic, do not present the same level of direct concern for backflow contamination as crawl spaces do. Therefore, regulations are stricter in crawl spaces to safeguard public health and ensure the integrity of the plumbing system.