A mathematical model was used to simulate the long-term movements of the high water slack longitudinal salinity profile in the estuary of the Sg Kuantan, Malaysia. The proven model was then used to predict the effects on salinity of increased abstractions from the estuary under various drought conditions. The predicted longitudinal profiles were used to estimate the restrictions on abstraction at four sites assuming different limits on the salinity of the abstracted water. The main conclusion of the study is that, in the design drought conditions given, increased abstraction of water with tolerable salinity would not be possible for much of the year at the present intake, JKR Kobat (10.9 miles from the sea). Salinity levels would be considerably lower if the intake were moved to a point 16 miles from the sea, but for the abstracted water to be free of salinity above 0.2 ppt chlorides the intake would have to be moved at least 18.5 miles from the sea. An intake 20 miles from the sea would be affected by salinity of 0.1 ppt chlorides only for 30% of each tide on the worst 19 days of a 1 in 50 year drought.