Osmotic pressure for seawater is around 27 atmospheres.

This would seem to imply that a column of seawater >272 metres high with an appropriate filter at the bottom should be able to produce fresh water under its own weight. Is there something wrong with my thinking on this?

dv said:

Osmotic pressure for seawater is around 27 atmospheres.

This would seem to imply that a column of seawater >272 metres high with an appropriate filter at the bottom should be able to produce fresh water under its own weight. Is there something wrong with my thinking on this?

Seems OK to me.

dv said:

Osmotic pressure for seawater is around 27 atmospheres.

This would seem to imply that a column of seawater >272 metres high with an appropriate filter at the bottom should be able to produce fresh water under its own weight. Is there something wrong with my thinking on this?

OK, I think I see where you are going with this. There does seem to be an OoM difference in the energy a pumping station uses and the energy required to lift water to that height.

This is where I loose (sic) it.

dv said:

Osmotic pressure for seawater is around 27 atmospheres.

This would seem to imply that a column of seawater >272 metres high with an appropriate filter at the bottom should be able to produce fresh water under its own weight. Is there something wrong with my thinking on this?

As Michael V says, that’s right. Several decades ago I did some calculations based on this idea. For example, put an empty pipe 270 metres long into seawater (such as the pylon for an oil platform), put an osmotic membrane at the bottom and you can pump fresh water straight out of the pipe (for the oil-rig workers). I ended up rejecting the idea as infeasible, it’s easier to pump the seawater onto the oil ring and then push it through a series of membranes onboard.

Because osmotic membranes are never perfect (have small holes or have too slow a flow-rate) the water quality you get out of your 272 m long column won’t be perfectly pure, so it’s better to run it though in a series of smaller stages.

you could pump the water into a tower at your leisure and allow water pressure to push clean water through a filter ?

if the pumps were powered by the sun or wind any temp shortfall of power would be catered for by the tank of accumulated water