Final answer:
Backwater valves are plumbing fixtures designed to prevent reverse water flow due to sewer backups and are a part of the plumbing system, much like air-filled tubes that prevent contamination by acting as air gaps near water faucets.
Step-by-step explanation:
Backwater valves are critical components in plumbing systems. They are designed to prevent the reverse flow of water, specifically in the case of a sewer backup. When asking about the listing of backwater valves, the most accurate category for them is Plumbing fixtures. Plumbing fixtures include a variety of components that are connected to the plumbing system, such as sinks, toilets, and yes, valves. The main function of these valves is to allow water flow in one direction and automatically prevent it from flowing backward, which can be particularly important during heavy rainfalls or sewer system malfunctions that could cause sewage to back up into a home or building.
Air-filled tubes, also known as air gaps, are often included near water faucets in plumbing systems to prevent contaminated water from siphoning back into the clean water supply. These air-filled tubes act as physical barriers to maintain the quality of drinking water. Water engineers and other engineering specializations play a significant role in the design and management of water treatment plants, ensuring the use of proper fixtures, like valves, to maintain the integrity of water systems.