As a hypothetical, say it became easy to grab water from objects in space and then move it places that needed (Africa / the gulf). What would the end results be for the global climate over time? Would you just end up with a flooded earth? Would temperatures rise or fall as time goes on?
https://calculatedearth.com/ allows you to see what would be left above water at a given amount of sea level rise. It’s not a complete answer to your question but you can use it to run animations with different ranges of added water depending on how crazy you want to get with your sci-fi scenario.