Floating Lake

Many consider water as a critical resource for humanity and its associated environment. To protect this resource, I am surrounded by water saving technologies: Low-flow showers, flow-restrictors on taps that aerate the water so it looks like there's more than there is & toilets that only flush 3.6 litres*.

This is understandable in Arizona, but Philadelphia nestles between two large rivers, there's plenty of water. Globally also, there is plenty of water, there's no water problem, it's a salt problem**. Now, this doesn't start as a problem, rain is freshwater, extremely fresh in most cases. The problem is that it often falls directly into salt water before we can get to it.

So, how about we pick a nice calm bit of sea with a reasonable rainfall. The equator is a good place to start looking, as rainfall and calm are features of equatorial ocean. The location should be near shore in relatively shallow waters so that some anchoring is feasible. Nearby land, especially mountains can encourage local rainfall also. Here we construct our nice freshwater lake.

Now, freshwater is less dense than seawater so, if you can separate it from the ocean, it floats. Let's start with a large steel floating ring. From the bottom of this we build a large plastic bag. Initially this could be filled with seawater and subsequently desalinated or filled by pipe from a land source. With a little bit of structural reinforcement from a very flexible wire/plastic mesh we should be able to harness the ~2% buoyancy and making a 2.5km deep lake will provide enough lift to raise the rim 50m from the sea surface.

Now you can stock it with freshwater fish, some floating plants to keep evaporation down and you have a nice freshwater lake that will even be able to supply water under pressure to places right on the shoreline.

* You do have to flush them twice, the orange man is right.

** Although I'll admit there are some local variations.