Need fresh water by the sea. Seawater RO VS RO from dehumidifer ?

[Laietanium]

Hi All,

I basically need to survive by the beach in a caravan, on a dry island, near the beach, with no fresh water available so I need to make it myself.

I have thought of two possible options but please let me know if you think there are other better methods. Both of my options use RO membranes.

Method 1) is to use Seawater RO membrane . I know there are ready solutions for this but they are so expensive I can't afford. I see the cheapest one is 250$ from FilmTec, are there any cheaper ones ? How would someone use the Seawater RO membrane , similar to household system ? Like Sediment - > Carbon -> RO -> Post ? I understand these seawater RO membranes need high PSI pumps but I guess thats not a problem.

Method 2) Use a dehumidifer and just Sediment-<Carbon->RO(with UV for viruses/bacteria ? ) this water.

Also, why can't I use simple RO membranes for seawater ? Whats the real difference between simple RO and SWRO membranes that makes SWRO so much more expensive ? Is it the salt rejection rate ? Or something else ? If it's the salt rejection rate , surely I could use 2 membranes or loop the water again through the RO membrane , surely that would do the trick ?

I have 3.6KW of Solar panels on the roof of the caravan and the island is very sunny and warm so I could always also distill some water but wouldnt that be a waste of energy ? I need the kwhrs for other things.

Thank you so much!

 

[davidcalgary29]

A DIY solar still or evapotranspiration system using plants can work in a pinch, but this is pretty harsh and gross (as is drinking from a dehumidifier or freezing seawater and using the freshwater ice on top). This isn't permanent, is it? There are a ton of better options for obtaining freshwater if you're off the grid.

 

[Laietanium]

Permanent. Can you please tell me better options ? Why RO seawater or RO dehumidifier is not a good option ? I cannot use the plants , they are rare and protected species, not much grows there.

 

[davidcalgary29]

Permanent. Can you please tell me better options ? Why RO seawater or RO dehumidifier is not a good option ? I cannot use the plants , they are rare and protected species, not much grows there.

Are you planning to live in a park or protected area? This will probably reduce your options. I can't really envision a dehumidifier system in a caravan, and a seawater membrane as you describe isn't going to produce very much potable water per day.

Is there some reason why you cannot simply set up a rain barrel/cistern system and have fresh water trucked to you?

 

[Malcontent]

Sea water reverse osmosis runs at 1000 psi. It's not quite the same as household RO. Everything is more expensive.

You can get a Katadyn Survivor 35 for $300 on eBay. People have survived months adrift with those.

 

[Laietanium]

Are you planning to live in a park or protected area? This will probably reduce your options. I can't really envision a dehumidifier system in a caravan, and a seawater membrane as you describe isn't going to produce very much potable water per day.

Is there some reason why you cannot simply set up a rain barrel/cistern system and have fresh water trucked to you?

Yes I will live by the beach in a public space,it's like protected forest of cedars. It doesnt rain for months and when it does , not much. Yes I could setup a barrel for the 2-3 winter months , but still it might not rain for a month. What's the problem with the dehumidifier running in the caravan ? I already have one 10lt/day, works fine and its really small. It's pretty big caravan ( 8meter x 2.5meter ). It's warm pretty much all year around and I have 3.6kw solar panels and lifepo4 batteries to store power . Also, what is the problem of passing dehumidifier water through RO/UV ?

Sea water reverse osmosis runs at 1000 psi. It's not quite the same as household RO. Everything is more expensive.

You can get a Katadyn Survivor 35 for $300 on eBay. People have survived months adrift with those.

Wow this Katadyn Survivor 35 looks quite cheap . I've seen the SWRO membranes require more PSI than normal RO membranes . Is this basically just a FilmTec SWRO membrane ( it costs around 250usd ) with a hand pump ? . I know many SWRO don't require 1000psi, so maybe it's one of those ? Most FilmTec SWRO are rated for 600-800 psi with a maximum of 1000-1200psi. Surely they would run at lower psi just not as efficient, right ? This Katadyn Survivor it seems like its a RO membrane without any sediment, carbon filter, UV lamp, is that really ok for everyday use ?

I know everyone says you must use SWRO membranes for seawater and normal RO membranes don't work , but why ? Why can't I use residential RO membranes instead of SWRO ? Is it the salt rejection rate ? Do they go bad with seawater ? If it is the salt rejection rate I could certainly use two residential RO membranes in series or just loop it through the same RO membrane ? I don't care about waste water . What would be the minimum pump for those low pressure SWRO membranes ?

I wouldn't mind like getting a filmtec SWRO for $250 and a pump , instead of the hand pump.