Here’s a concept that purports to be a viable way of growing crops in a device that floats in salt water. As shown in this video, water naturally passes through a filter that traps the salt.
Sorry, that’s not going to happen. The desalination of water requires a lot of energy. Salt dissolves very easily in water, forming strong chemical bonds, and those bonds are difficult to break. Energy and the technology to desalinate water are both expensive, and this means that desalinating water can be pretty costly.
It also means that this concept is ahhhhhh..no.