Which statement best describes infiltration?

Which statement best describes infiltration?

• A. Water entering through roof drains
• B. Water that seeps into joints and cracks from surrounding soil
• C. Water from leaks inside the building plumbing
• D. Water that leaves the sewer system

Answer: (B)

Infiltration is water from the surrounding soil that enters the sewer system through defects in the pipes and joints, such as cracks or loose connections, allowing groundwater to seep in. The statement describing water seeping into joints and cracks from the surrounding soil matches this idea exactly, which is why it’s the best description. This is different from surface water that can enter the sewer during rain through roof drains or yard drains (inflow), water that comes from leaks inside building plumbing (internal sources), or water that leaves the sewer system instead of entering it (exfiltration). Infiltration focuses on groundwater entering through the infrastructure itself, not water from surface sources or interior leaks.