After reading @Lukian's post about econcretetech precast specially designed concrete blocks for sea walls [agnostic.com] , I started looking around and found this video on a project using seawater for an agricultural system. Perhaps the most interesting bit was in using halophyte plants [en.wikipedia.org] , which actually thrive with salty water. I could easily see this being done in the US. Unfortunately, I haven't been able to find any recent information on this project. Perhaps it was abandoned. However, there appears to be other similar ongoing projects using seawater.