In plumbing, what does “drainage” refer to?

In plumbing, the term "drainage" specifically refers to the removal of wastewater from buildings. This includes the flow of used water from sinks, toilets, showers, and other plumbing fixtures into the sewer or septic system. Efficient drainage is crucial for maintaining sanitary conditions in a structure, as it prevents water accumulation and potential contamination. Properly designed drainage systems allow wastewater to be transported away from living environments, contributing significantly to public health and hygiene.

The other options focus on different aspects of water management: introducing fresh water pertains to supply systems, filtration refers to the process of purifying water, and the collection of rainwater is often related to water conservation or stormwater management systems. None of these options encompass the essence of what drainage specifically addresses.