About Surface water sources:

• There are four major sources of surface water. These are rivers, lakes, ponds, and tanks.
• The mean annual flow in all the river basins in India is estimated to be 1,869 cubic km.
• However, due to topographical, hydrological and other constraints, only about 690 cubic km (32 per cent) of the available surface water can be utilised.
• Water flow in a river depends on size of its catchment area or river basin and rainfall within its catchment area.
• There are three types of surface water: perennial, ephemeral, and man-made.
• Perennial, or permanent, surface water persists throughout the year and is replenished with groundwater when there is little precipitation.
• Ephemeral, or semi-permanent, surface water exists for only part of the year. Ephemeral surface water includes small creeks, lagoons, and water holes.
• Man-made surface water is found in artificial structures, such as dams and constructed wetlands.

Source: NCERT