After many long years this results in plentiful groundwater that slowly moves downriver through the aquifer. Southern Taiwan has a six-month dry season, and people in the Pingtung Plain, where no artificial reservoirs have been built, must depend upon groundwater from summer rains infiltrating the soil for domestic, agricultural and aquaculture purposes. Prior to the 1980s an average yearly groundwater recharge of 1 billion tons was more than enough.
（圖一）台灣南部降雨分布極不平均，冬季 11 月到隔年 5 月，只降下全年雨量的 1 成；在長達半年的旱季中，沒有水庫的屏東平原，就是靠夏天降雨下滲的地下水提供民生、農業、養殖等各類用水。