Is anyone aware of any regulations pertaining to where you can make water with a RO unit offshore? For instance distance from land and or depth of water?
Not sure what flag state your vessel is but for British registered vessels there is a 20 mile limit for the production of FW from low pressure evaporators or RO plants. Can extend further where estuarial pollution is a concern.
By law you should have a full set of M notices on board the vessel, If British and above 12m in length.
You can make potable water with a reverse osmosis unit onshore. I suppose you are concerned with the environmental legeslation related to the discharge. I don't know the answer.
Find the US Coast Guard regulations it Title 33 of the Code of Federal Regulations.
If on a US platform, check the 30 CFR 250 for the Minerals Management Service, Department of the Interior -- Oil and Gas and Sulfur Operations in the Outer Continental Shelf.