What does "drainage" refer to in the UPC?

In the context of the Uniform Plumbing Code (UPC), "drainage" specifically refers to the process of removing wastewater and sewage from plumbing fixtures, such as sinks, toilets, and showers, and transporting that waste to a sewer system or treatment facility. This definition aligns with the necessity for effective plumbing systems to manage and eliminate waste to prevent health hazards and environmental contamination.

Proper drainage is essential for maintaining sanitary conditions in buildings and ensuring that wastewater is handled safely and effectively. This involves a network of pipes, fittings, and fixtures designed to convey waste away from where it is generated to a point where it can be treated and safely disposed of.

The other choices do not align with this definition of drainage. The collection of clean water from rain and snowmelt is related to stormwater management rather than waste disposal, recycling greywater for non-potable use falls under water re-use practices rather than drainage, and the treatment of water before entering the plumbing system pertains to water quality management rather than the removal of waste. Therefore, the most accurate understanding of "drainage" is the process described in the chosen answer.