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Old 18-10-2014, 18:02   #1
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Question Filtering Salt Water?

No, not for drinking.

For use in washing dishes, laundry, shower, etc.

Oil, sewage, ocean critters - it would be nice to be able to filter these out (or at least the bulk of them). Could a strainer + basic charcoal filter do a decent job? Is there anything fundamentally different in filtering salt versus filtering fresh?

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Old 18-10-2014, 18:20   #2
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Re: Filtering Salt Water?

I use a simple fine SS mesh strainer.

Watermakers use serious pre-filters, and might be something to adapt if you want a higher level of filtration.
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Old 18-10-2014, 18:34   #3
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Re: Filtering Salt Water?

There would be no need for a charcoal filter because that is used to remove organics and some halides from drinking water - no use in sea water.

Likewise for oil and sewage - not a lot a filter will do for you there.

If you want more filtering than is present in a typical fine mesh strainer, a 5-20uM wound string or pleated filter, like used for watermakers, would work. However, like in watermaker usage, these will grow stinky critters very quickly and wouldn't have the luxury of fresh water flushing to kill/remove them.

Do you really want to do laundry in salt water at all regardless of how much it is filtered? Personally, if the water isn't clean enough to do the things you want using a simple mesh filter for seaweed, I wouldn't want to use it for anything other than flushing the head.

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Old 18-10-2014, 20:48   #4
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Re: Filtering Salt Water?

On the hook, the water is generally clean enough for dish washing. I never even worry about it. Just rinse in fresh and life is good. Laundry is the same, the water will be cleaner then the cloths going in it anyway.

Mind you I'll NOT use sea water in a marina. But on the hook, it's not a problem at all.
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Old 18-10-2014, 21:15   #5
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Re: Filtering Salt Water?

Thanks lady and gents for the response so far,

To clarify something, I don't plan to have a regular raw water intake in the hull. I'm just going to use a couple day tanks which I'll fill from on deck: was thinking I'd use some cheap manual pump with a hose overboard - so I have no use for a filter that requires an electric pump (as I assume a watermaker type filter requires?). It's got to be something I could jury rig to a manual pump.

Anyway, a simple way to solve the biologic aspect of the problem just came to mind. I could just dump some bleach in the tanks. Done.

So the only issue then is chemical pollution. A carbon filter can handle some chemicals (just checked) but not oil/diesel/gasoline, which are probably the biggest offenders near shore.
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Old 18-10-2014, 21:21   #6
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Re: Filtering Salt Water?

like Colemj states, the problem with filtering salt water is you'd need to thoroughly rinse the filter with fresh water so anaerobic growth doesn't take over. You might as well use the fresh water yourself instead.
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Old 18-10-2014, 21:26   #7
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Re: Filtering Salt Water?

Quote:
Originally Posted by Tellie View Post
like Colemj states, the problem with filtering salt water is you'd need to thoroughly rinse the filter with fresh water so anaerobic growth doesn't take over. You might as well use the fresh water yourself instead.
Understood, but how long do you think that would take to happen with a simple carbon filter? They're only $5-$10 a pop, so frequent replacement (within reason) might be acceptable.
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Old 18-10-2014, 21:47   #8
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Re: Filtering Salt Water?

Every 6 or 7 days i am guessing

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Old 18-10-2014, 21:59   #9
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Re: Filtering Salt Water?

Quote:
Originally Posted by Dulcesuenos View Post
Every 6 or 7 days i am guessing

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Ah, that's not so good...

Though, on the other hand, I suppose I could have such a gizmo rigged up, and just use it from time to time when I think the water looks/smells especially funky.
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Old 18-10-2014, 22:01   #10
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Re: Filtering Salt Water?

Quote:
Originally Posted by KISS View Post
Understood, but how long do you think that would take to happen with a simple carbon filter? They're only $5-$10 a pop, so frequent replacement (within reason) might be acceptable.

We get the anerobic stink in the head flush water within hours in certain waters. The filters would be just as quick


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Old 18-10-2014, 22:10   #11
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Re: Filtering Salt Water?

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We get the anerobic stink in the head flush water within hours in certain waters. The filters would be just as quick


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....and that's even worse.

I wonder if this bacterial growth effects the filter's ability to remove chemicals? If not, then it would still be fine for my needs. It doesn't matter if the water is crawling with bacteria after filtration as long as I bleach its brains out before use.
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Old 19-10-2014, 06:33   #12
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Re: Filtering Salt Water?

I'm not sure what type of "chemicals" you think are in clean sea water. Since oil-type stuff is not filtered, just what are you hoping to avoid?

If you use an impregnated carbon filter (the cheap kind), it will probably be fully adsorbed with halides the first time you use it. If you use a carbon block filter (the best kind), it will probably plug solid from sea life the first time you use it, or become useless when a small amount of growth forms on it.

BTW, watermakers use common under-sink filter housings and filters. They are passive filters with no pump, etc associated with them. So people's experiences with using their watermaker filters in seawater are directly related to your questions.

Even with using bleach in seawater, I suspect your tanks will be a biological mess in a year. I am not catching on to the purpose of seawater day tanks - why not just a thruhull intake? If you are worried about the integrity and safety of a thruhull, that is an easily solvable problem.

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Old 19-10-2014, 06:41   #13
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Re: Filtering Salt Water?

i do not use red tide water for dish washing, otherwise i merely use a bucket to grab it out frim under boat and wash dishes.
aint dead yet.....
not even ill..
use some sea water for cooking taters also... aint ded yet....
also use it for washing my teak wood rails and house wood.....
you folks on low freeboard boats essentially drink the stuff when it comes over your half my height bows, what is the problem with washing and using it for cooking....
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Old 19-10-2014, 07:10   #14
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Re: Filtering Salt Water?

I can't stand it...

a. Carbon filters are used to absorb chlorinated organic chemicals, not "halides." Saltwater does not contain these in significant amounts. While chloride ions will cause some interference, it is not the sort you are thinking of.

b. Yes, a carbon block will foul very quickly without effective pre-filtration. A ceramic element (cleanable) would be a far better choice. However, without an electric pump it would flow well. Google "Survival" and you will find some bucket filter ideas. But I think avoiding the electric pump is just being thick; generally electric pumps are more dependable than manual pumps; fewer moving parts.

c. Granular carbon filters loose most of their chemical absorption capacity quickly due to bio-fouling; they become a place for the sealife to live. This does not cause very rapid fouling if there is some prefiltration, but they do stop absorbing organic chemicals efficiently. Google "activated carbon biofiltration."

d. If there were oil/gasoline, they float. Draw water 5 feet down. But honestly, if there is ANY petrol you can notice, draw water. Yes, carbon is and effective and common way to remove petroleum, but it smarter to move.

e. The stink is mostly hydrogen sulfide from the bacteria converting sulfate in the seawater to sulfide in the absence if air (bugs dying has little to do with it). Bleach will oxidize the sulfide back to sulfate and the smell will vanish in seconds.

And the whole thread is dumb, since there is little purpose in filtering water for these uses. Either get tap water form shore and filter/chlorinate, or draw clean off-shore water. There is also rain.

But this is what you are looking for. Will work in freshwater too.

http://www.pssurvival.com/PS/Water_Purification/Filtering/Gravity_Feed_5_Gal_Bucket_Ceramic_Water_Purifier_2 011.pdf

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Old 19-10-2014, 07:11   #15
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Re: Filtering Salt Water?

By the way, put your salt water intake a couple feet down and you do reduce the potential problem . . . . . Oil floats as do many of the other nasties . . . But there are just simply some ocasional filthy harbors where you are not going to want to touch the water no matter. Even folks with full water maker filter systems will not run their water makers in these harbors.
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