Originally, the area of supply covered only 44.8km² (17.3 sq.miles). The supply area was subsequently increased in stages over the years to cater for the water demand of developments outside it as they could not be conveniently or feasibly supplied by Jabatan Kerja Raya. In 1963 and 1973, the supply area was increased to 90.7km² (35 sq. miles) and 225km² (87 sq. miles) respectively. The supply boundary was extended further in 1988 to cover the current area of 730km² (282 sq. miles).