The report discusses how water flows under pavements and the importance of drainage systems in their design, construction, and maintenance. It explains the sources of water in pavements and how it moves within them. The report also covers factors like highway design, surface drainage, climate, and soil properties that affect pavement drainage. It describes the design of subsurface drainage systems, how to remove excess water, and the use of filters. Additionally, it talks about rehabilitating existing pavements with subdrains and installing new drainage systems like edge drains.