ABSTRACT
18 Groundwater Rainfall (precipitation) is the ultimate source of all fresh water, and when it lands on the ground surface it is dispersed in three ways: Evapotranspiration: combination of evaporation from open water and transpiration by plants, both returning water to the atmosphere; in temperate climates it may vary from 20% of the rainfall on open hills to 70% from wooded lowland. Runoff: surface water flow into streams and rivers; increases with low rock permeability, steep slopes, intense rainfall and urbanization. Infiltration: seepage into the ground to become groundwater; important on permeable rocks, and where runoff is slow. Groundwater is all water flowing through or stored within the ground, in both rocks and soils; it is derived from infiltration, and is lost by flow to surface springs and seepage out through the sea bed. Water budget is the balance of flows for any part or the whole of a combined groundwater and surface water system; a natural budget is easily disturbed by man's activities, notably where land drainage or urbanization reduce infiltration and groundwater recharge.
