Anti-scalant process for an osmotic unit

An osmotic process comprising for a first period, passing a draw stream and a feed stream through an osmotic unit having a semi-permeable membrane, permitting the passage of water but not salts. The feed stream is an aqueous stream with a lower salinity than the draw stream. The feed stream has a scalant with a concentration above saturation in a region on a feed side of the semi-permeable membrane. The draw stream passes over a draw side of the membrane and the feed stream passes over the feed side so water passes across the membrane from the feed stream to the draw stream. For a second time period, the flow rate of the draw stream is lower than the flow rate in the first time period, and the feed stream passes over the feed side such that the concentration of the scalant in said region is reduced.