A process for treating a water stream containing dissolved organic carbon and dissolved salts comprises subjecting the water stream to reverse osmosis after a pre-treatment step to reduce the amount of dissolved organic carbon directed in water to the reverse osmosis treatment step. The preferred pre-treatment step is a membrane treatment step such as nanofiltration. The process enables treatment of complex effluents including mixtures of domestic and industrial effluents. Treated water may be recycled and a treatment plant (100) employing the process forms another aspect of the invention.