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Water filtration/purification for non-pressure systems

Mar 26, 2011
2,910
Corsair F-24 MK I Deale, MD
For those with pressurized systems, there are a wide variety of home and RV systems that can remove chlorine and cysts, and even bacteria. However, they generally used carbon block filters and require significant pressure drop to work.

What do people with hand or foot pumps do, other than a little pre-filtration, chlorinate, and possibly de-chlorinate with granular carbon? It strikes me that carbon block filters and Seagull filters won't work. I believe I read somewhere that a Seagull filter could work on the pressure side of a foot pump, though I'm sure it would not work on the suction side of a hand pump.

Experiences?
 
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Oct 19, 2017
6,861
O'Day 19 Littleton, NH
I am interested in putting a filtration system on Dragonfly. As a hiker, I have been using the Squeeze system by Sawyer

https://www.amazon.com/gp/aw/d/B005...M+hyL&ref=plSrch#immersive-view_1512216345019
It uses a micro-fiber filter. I don't think there is any carbon involved.

I am going to make my own pressurized water tank out of a couple of large pvc pipes connected together on either side of the CB trunk, adapt a bicycle pump or something, so I can have a shower in the cockpit.

I'm really interested in some sort of watermaker that either uses condensation or reverse osmosis. However, I can't afford a system that costs more than my boat. I think there may be some possibilities around the use of mangrove roots:
https://www.nature.com/articles/srep20426
- Will (Dragonfly)
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
There are some people with conditions which make it necessary. However, unless you have some special medical condition, if you have a little chlorine in the water, I think it is your friend, not your enemy. I think that the number one problem with water systems is usually the result of "goo of life" smell (i.e. usually sulfur dioxide like, rotten egg smell).

I don't think a carbon filter would really block or materially affect a Whale foot-pump. The first thing that you should have is a -- do you have one of those little, inexpensive "screen" filters for gross particulates. Then you can put a hardware store, household filter body in line. (That seems to me like overkill, but different folks, different strokes.) Then you can go with various degrees and types of filters that range up to carbon blocks.

We've sailed and been based in the Chesapeake for a lot of years on three boats. The only carbon filter is on the freshwater flush feature of our J/Boat's RO watermaker. That filter body is their simply to protect its membrane which would be damaged by chlorine. Our prior Pearson 35 and Sabre 42 boats had none of that. If you have a "clean" (reasonably purified) tank and lines, just using municipal water which is cycled through the system every two weeks or so seems to be fine. Peggy's book and posts on boat plumbing systems (as well as, a simple web search) will give you guidelines for purification of you on board system.

The filter will "mask" the underlying issues in the tank. You should occasionally purify your tank anyway, even if you have a carbon block filter. Let your nose and taste be the guide.

Also, if you have a carbon block filter -- you will be needing to deal with that as part of your winterizing process. You'll need to either take it off-line, drain and dry it over the winter; or, you'll have to change it every year (which it really won't need, with your actual water use); or, you'll have to deal with the result of it being soaked in potable antifreeze. The potable anti-freeze's flushing will take you a LOT of water and futzing around :^))). In that case, you'll probably want to make sure you pull the filter, dry it out, flush the system without the filter in the Spring, and then reinsert. I know this because of a friend who put one in on their pressurized boat, and then was griping about it. :^)))))
 
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Oct 19, 2017
6,861
O'Day 19 Littleton, NH
if you have a little chlorine in the water, I think it is your friend, not your enemy.
The formula is 2 drops per gallon of household chlorine bleach, over night (for campers/hikers ...). I use to throw a cap full of bleach into the 250 gallon stock tank every time I refilled it, for our horses. If I didn't, green algae grew. It looked pretty bad. Just a tiny amount of bleach cleared it right up. The horses never had any problems and no bleach smell by the next day. Chlorine is still the cheapest, most extensively used water purification process in the world.
I live on a well in a cabin in the mountains of New Hampshire so no chlorine, I smell it in the water at every hotel I visit, because of that.
By the way, my main water filter is not carbon based. I buy the filters from Lowes.

$10.98
- Will (Dragonfly)
 
Mar 26, 2011
2,910
Corsair F-24 MK I Deale, MD
Let me clarify about carbon filters.

Most carbon filters are granular carbon, and do not appreciably affect flow. They remove chlorine by oxidation and some tastes by adsorption. The do not remove suspended solids or microbes, and may actually help the microbes grow by removing chlorine, providing surface area, and gathering the food in one place.

Carbon block filters do all of the above, plus, with a pore size <0.5 microns, remove gardia and cryptosporidium cysts, and significantly reduce bacteria and viruses. However, they require pressure to get flow. Seagull is in this catagory. so are most NSF 53 certified filters rated for cyst removal. The reason for the interest in cyst removal is that chlorine has trouble with these.
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The main Chesapeake area problem is skunky water. The water contains significant amounts of sulfate, and if any bacteria survive, they convert that into sulfides, which taste bad. So fresh smelling water pretty much requires chlorine, and removing chlorine pretty much requires carbon. As for cysts, the risk is probably conversational at most. But some folks travel far more widely, into the third world, where the needs will be greater. And I'm not to sure what I think of the water in some marinas. Some of the wells have obvious problems.
 
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Mar 1, 2012
2,178
1961 Rhodes Meridian 25 Texas coast
I have a filter installed after the foot pump, that came from a commercial airliner. Has drop in filters that are supposed to be good for 3000 gallons. I change every 6 months. I also clorinate the tanks once every year at minimum. More often if needed.
 
Oct 19, 2017
6,861
O'Day 19 Littleton, NH
pore size <0.5 microns, remove gardia and cryptosporidium cysts, and significantly reduce bacteria and viruses.
I understand viruses are much smaller and harder to filter out, however, less prevalent in water to begin with. Not that that means they can be ignored. Pool sanitation systems have mostly moved away from chlorine to bromine or salt based system, probably because of the smell. My pond filter used both an algae growth encouraging mesh that "eats" unwanted biota and a UV filter in line. Many filtration systems for large flow capacity use sand to filter out the things that make water murky. A multi stage system that steps through a macro filter, to a micro filter with a chemical or UV biotic killer in between would probably be the only way you can get good, reliable, potable water without pressure. Off course some pressure to move the water is required no matter what, I take it, thinwater, you want something that doesn't require more pressure than gravity feed over about a 2 meter drop. The answer could be in multiple, parallel, filters to reduce resistance. Like for an electrical circuit.
You talk about the Chesapeake bay water like it's what you are sourcing. But, desalination will get rid of everything. The only three ways I know for doing that is distillation, condensation, or reverse osmosis. Reverse osmosis needs a lot of pressure. That's why I am interested in mangrove roots.
- Will (Dragonfly)
 
Mar 26, 2011
2,910
Corsair F-24 MK I Deale, MD
I understand viruses are much smaller and harder to filter out, however, less prevalent in water to begin with. Not that that means they can be ignored. Pool sanitation systems have mostly moved away from chlorine to bromine or salt based system, probably because of the smell. My pond filter used both an algae growth encouraging mesh that "eats" unwanted biota and a UV filter in line. Many filtration systems for large flow capacity use sand to filter out the things that make water murky. A multi stage system that steps through a macro filter, to a micro filter with a chemical or UV biotic killer in between would probably be the only way you can get good, reliable, potable water without pressure. Off course some pressure to move the water is required no matter what, I take it, thinwater, you want something that doesn't require more pressure than gravity feed over about a 2 meter drop. The answer could be in multiple, parallel, filters to reduce resistance. Like for an electrical circuit.
You talk about the Chesapeake bay water like it's what you are sourcing. But, desalination will get rid of everything. The only three ways I know for doing that is distillation, condensation, or reverse osmosis. Reverse osmosis needs a lot of pressure. That's why I am interested in mangrove roots.
- Will (Dragonfly)
How prevalent viruses are depends on the water and where you are. Cholera, for example, is a still a problem in many areas. Viruses are greatly reduced by electrostatic adsorption mechanisms in carbon block filters, not by physical exclusion. This is the claim of Seagull, for example. However, viruses are easily deactivated by chlorine and area more easily treated in that way.

I said "Chesapeake area" but I was referring to freshwater. Many of the wells are in high sulfate soils, and through the water is fresh, it does not react well to storage. I understand desalinization; I have engineered and installed large scale RO and distillation plants.

No, parallel flow is not going to work for any physical exclusion or carbon block filter that I know of. They are designed for 60-100 psi and 1-2 psi isn't going to do much. There are a few slow-drip media that work, sometimes packaged in pitchers or bowls. That is one possibility.

UV, with cleaning requirements and the need to power the bulbs through the warm-up period, is a non-starter for most smaller boats.
 
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SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Aren't there different criteria for the carbon block filters? 5 micron rating vs. finer, etc. At your flow rate, I don't think the pressure drop is going that big a deal with a proper foot pump (Say a Whale pump)?

While the carbon block filter is great for chlorine -- it's not so great for pesticides and other chemicals?

Thinwater,
Is it the relatively shallow Chesapeake that is the basis of your nom de web? Or is it your work on large water purification systems :^))))?
 
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Oct 19, 2017
6,861
O'Day 19 Littleton, NH
They are designed for 60-100 psi and 1-2 psi isn't going to do much.
This is such an interesting thread to me. I'm very much interested in pouring something in Dragonfly and have only just begun to look into it.
My house system is charged at 40psi which seems like plenty for any demand I put on it. 1-2psi hardly seems like enough to get water plumped out of a bilge. What pressures are you really looking at for your criteria? I would love to be part of the team that finds the answer to your question.
How about condensers for extracting water from the air? No contaminants at all.
- Will (Dragonfly)
 
Jun 6, 2006
6,991
currently boatless wishing Harrington Harbor North, MD
I guess I'm dense. If you clean your tank with a chlorine shock treatment and then don't dump dirty water into it you should not have to worry about virus or other tiny bugs.
what source are you using to fill the thank? Potable water has a pretty good record of not causing health problems so if your tank and system are clean you should only need filtration to protect the pump.
 
Mar 26, 2011
2,910
Corsair F-24 MK I Deale, MD
Aren't there different criteria for the carbon block filters? 5 micron rating vs. finer, etc. At your flow rate, I don't think the pressure drop is going that big a deal with a proper foot pump (Say a Whale pump)?

While the carbon block filter is great for chlorine -- it's not so great for pesticides and other chemicals?

Thinwater,
Is it the relatively shallow Chesapeake that is the basis of your nom de web? Or is it your work on large water purification systems :^))))?
While you can get 5 micron rated carbon block filters, whats the point if they arn't removing cysts? Might as well use granular carbon.

Granular carbon is less expensive, and thus is the first choice for organics removal. That said, I'm not concerned about pesticides in tap water and carbon blocks are about equally effective.

I have not tried one with a foot pump. I would like to hear the feedback. I know when my tank was full I would still get a trickle (the tank is several feet above the faucet), but I'm guessing the flow would be less. I know that a CBC-5 reduced the flow at 65 psi to the point where I up-graded to a CBC-10 and then a FloPlus 10 before I got good flow. I have heard mixed reviews of the practicality of using a Seagull filter with a foot pump. It is well known that the backpacker fine filter systems (First Need etc.) take some serious pumping to fill a canteen. For sailors with rocker pumps on the faucet, they would not tolerate the suction.

PUR pitchers would work, but they don't seem to practical on a small sailboat.

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I've always had shoal draft multihulls. I think 5 feet is really deep, board up. I've never had a slip deeper than 3 feet at extreme low tide.
 
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