Waipahu, Hawaii, United States [CDP]; population was 31,435 in 1990; housing units was 7,739 in 1990; location is 21°23'N 158°1'W; land area is 2.57 square miles (1,644 acres); water area is 0.06 square miles (39 acres); FIPS code is 79700 [SourceCBP]