Jeju has annual average 3.952 billion m³/year rainfall.
Approximately 24.5% of the rain fall(970 million m³/year) goes out to sea through rivers and 34.9% (1,379 million m³/year) is lost in air through evaporation
and the remaining 40.6%, i.e.1.604 billion m³/year is penetrated into the aquifer.
Excessive pumping of groundwater can cause the groundwater level decrease resulting in seawater intrusion.
Therefore, the Jeju province has actively implemented the groundwater protection and management policy
that regulates the use and development of groundwater,
including the groundwater sustainable yield of 652 million m³/year that is 40.6% of groundwater recharge volume.