Abstract: Apparatus for discharging effluent from a sea-based vessel (10) comprises a branched pipeline (22) which is disposed on the seabed (18). The vessel (10) carries a large-scale desalination plant (12), and the effluent, which is in the form of concentrated brine, is pumped through the branched pipeline (22) to a plurality of discharge locations on the seabed. The branched pipeline (22) includes a number of flexible discharge pipes (26a d) which fan out from a common location (30) towards open ends (28a-d). The open ends (28a d) are remote from each other, and the effluent is discharged simultaneously through the open ends (28a d) causing it to be dispersed effectively without harming surrounding eco-systems. In an alternative arrangement, a vessel-based water purification plant (10) is connected to a freshwater pipeline (16) and to a discharge pipeline (22), each of which is disposed on the seabed (18).