Complex sentence: At present, the total capacity of the three factories is about 20 million gallons per day (Mgd), of which 3 Mgd is used for indirect potable use, contributing 1 percent of Singapore's potable drinking water requirements of 300 Mgd.
Split into simpler sentences: At present, the total capacity of the three factories is about 20 million gallons per day (Mgd). About 3 Mgd of this is used for indirect potable use, which contributes 1 percent of Singapore's potable water requirements of 300 Mgd.