Caring for Dock Water Filter

[Muaddib1116]

In an effort to keep my water tanks as clean as possible, when I fill up from a dock supply, I've been using a 10 inch filter 5 micron charcoal filter to remove chlorine and particulates. I am considering going to a multi-stage setup, 2 or 3 filters. What I'm curious about is, since this is not a full time setup, I store it in the lazarette with my drinking water hose between fillups, should I try to drain and dry the filter(s) between uses? or leave the filter housings full of water? or not care and leave it as is, at whatever level of water there is?

[Lepke]

If you don't want marine growth, you should drain the filters. Probably dry them, too. Although if your marina water supply is city water, there's probably chlorine in the water, so just your carbon filter and anything after.

[Muaddib1116]

Great, thanks!

[sailorboy1]

I would stop using the carbon filter if the only reason is you what "clean" water. The chlorine is it it for a reason.

And I would store the filter full of water to keep the carbon from being coming a stuck together ball. The water was disinfected when it went it so it isn't likely to become "buggy", but if it does just flush it out. I have a DI resin filter I have from back when I needed to make pure water for the battery and it has been over a year and it hasn't growth anything in it.

[Muaddib1116]

My reason for removing the chlorine is so that when my watermaker backflush runs, there is less risk of damage to the membranes.

[thinwater]

Originally Posted by Muaddib1116

My reason for removing the chlorine is so that when my watermaker backflush runs, there is less risk of damage to the membranes.

Then put the carbon filter ONLY on that line.


At actual fill rates, you carbon filter is probably only removing less than 1/2 of the chlorine. A filter on the backflush line will be more effective.


IMO, the best fill-up filter is a 1 micron bag, which does not remove chlorine and can easily be dried between uses. Also works on rainwater and water from jerry cans. Washable, at least a few times.



https://www.practical-sailor.com/bel...y-water-filter

[Ded reckoner]

As you mentioned, chlorine is destructive of membranes. That's what chlorine does; it breaks chemical bonds. Chlorine is put into drinking water to kill things that are alive like bacteria, so the water is safe to drink. You are a large enough mammal, the chlorine isn't going to kill you, but I would recommend using an activated charcoal filter at the faucet or in a pitcher before drinking. In any case, removing chlorine from water the membrane contacts is important.

The information on some of the 10in activated charcoal filters indicates their lifetime is 2 months or 2000 gallons of water, whichever comes first. Other information indicates the filter is 95% effective removing chlorine. This would be at low flow. At higher flow rates, the efficiency will drop because the residence time of the water in the filter is shortened. At 95% efficiency, a single filter at the dock will leave 5% of the incoming chlorine. It you put two filters in series, it will leave 0.25% of the incoming chlorine. You will draw this water in your tank down by drinking and otherwise using it, and then use your watermaker to add more water to your tank. So, whatever residual water in your tank that had chlorine is now diluted by volume with the clean watermaker water. This dilution is helpful for lowering chlorine levels in the tank further.

My watermaker system has an activated charcoal filter for backflushing after watermaking. This will reduce chlorine levels again at 95% efficiency. No chlorine is good for a membrane, but this gets levels down a lot.

I use a single filter at the dock myself. I shake the filter dry and store it in a locker in a ziplock bag until the next use.

[Muaddib1116]

Originally Posted by thinwater

Then put the carbon filter ONLY on that line.


At actual fill rates, you carbon filter is probably only removing less than 1/2 of the chlorine. A filter on the backflush line will be more effective.




IMO, the best fill-up filter is a 1 micron bag, which does not remove chlorine and can easily be dried between uses. Also works on rainwater and water from jerry cans. Washable, at least a few times.



https://www.practical-sailor.com/bel...y-water-filter

So it seems like there are a few concerns. The chlorine is good for preventing growth in my tanks, but bad for my watermaker membranes. If I'm filling through a charcoal filter with dock water pressure, that will only remove half the chlorine? Isn't that good then? There's still some chlorine, but it's reduced, so that the inline backflush filter can remove most of the rest? rather than putting the chlorine removal all on the backflush filter?

Also, I have SS water tanks, isn't chlorine going to increase the chance of corrosion?

This isn't a huge deal while I'm in the US, but if I travel down into the Caribbean, isn't it possible I'll be glad to have more filtration from the dock supply?

[sailorboy1]

If you are using enough dock water to be concerned you probably don't need and are using your watermaker. Flush it out and pickle it!

[thinwater]

Originally Posted by Muaddib1116

... Also, I have SS water tanks, isn't chlorine going to increase the chance of corrosion?...

No, not at the levels present in tap water (1-3 ppm residual, vs. 25,000 ppm chloride in seawater, and it is the chloride that causes the trouble). Internet myth. This has been exhaustively studies by both plumbing and chemical groups.



Also, normally the chlorine removal life is MUCH longer than the taste/odor life, because the mechanisms are completely different. Carbon adsorbs tastes etc. Carbon is sacrificially oxidized (burned up) to remove chlorine.

[Muaddib1116]

Originally Posted by thinwater

Also, normally the chlorine removal life is MUCH longer than the taste/odor life, because the mechanisms are completely different. Carbon adsorbs tastes etc. Carbon is sacrificially oxidized (burned up) to remove chlorine.

The life of the filter? Wouldn't carbon being sacrificially oxidized make the chlorine removal life shorter? What are the implications of this?

[svfinlandia]

Originally Posted by Muaddib1116

So it seems like there are a few concerns. The chlorine is good for preventing growth in my tanks, but bad for my watermaker membranes. If I'm filling through a charcoal filter with dock water pressure, that will only remove half the chlorine? Isn't that good then? There's still some chlorine, but it's reduced, so that the inline backflush filter can remove most of the rest? rather than putting the chlorine removal all on the backflush filter?

Also, I have SS water tanks, isn't chlorine going to increase the chance of corrosion?

This isn't a huge deal while I'm in the US, but if I travel down into the Caribbean, isn't it possible I'll be glad to have more filtration from the dock supply?

Someone with more knowledge can correct me if I’m wrong, but chlorine should not be a problem for stainless steel tanks. Aluminum tanks are the ones that do not like Chlorine.

Al, S/V Finlandia

[sailcrazy]

Muaddib1116-I'm with you. My water tanks are s/s, but the big concern is to lower the Chlorine level in my water tanks. My water maker supplies water to 3 of my 4 tanks. When I Fresh-Water-Wash after making water, I use water from those same 3 tanks. I do have a carbon filter on that water supply line, but the lower the Cl level in the tank the less that filter needs to catch enroute to the membrane. There is no Chlorine in those tanks after making-and using- water in those tanks, as we seldom go into a marina. But when we do, and elect to put on water from the marina, I want the water in those tanks to be as Chlorine-free as possible. The Cl contact time from the municipal water plant, thru all the city pipes, to the marina, and then to my slip should be enough to kill any relevant bugs.
Regarding the 5mic Carbon filter in my dockside water transfer cannister-I've often wondered what the best way to keep it viable may be. For a time, I left it in the drained canister, stored either in the Lazarette or our fwd head. But after reading here, I'm going to start taking it out, drying it, and then storing in a zip-lock bag until needed next time. Keeping the canister full might work, but that could be tough to do. And, if it's been 4-5 months since I last used it, I'll just break out a new one!

[Muaddib1116]

Thanks for all the replies guys. Since the primary issue seems to be chlorine or not chlorine, what do you guys recommend if you only fill your tanks from your watermaker? add chlorine to keep the tanks clean and then strip it back out with your backwash prefilter? I've never read or heard anyone recommend that. So why not try to get my water as close to watermaker purity as possible when filling from the dock?

[rslifkin]

Originally Posted by Muaddib1116

Thanks for all the replies guys. Since the primary issue seems to be chlorine or not chlorine, what do you guys recommend if you only fill your tanks from your watermaker? add chlorine to keep the tanks clean and then strip it back out with your backwash prefilter? I've never read or heard anyone recommend that. So why not try to get my water as close to watermaker purity as possible when filling from the dock?

Realistically, lightly chlorinating and then stripping it back out would be ideal, but almost nobody bothers to do it (and if you're turning the water over quickly it's less of a concern anyway). Water coming out of the watermaker should already be pretty pure, so if the tank, etc. are clean, it should take very little chlorine to produce a reasonable chlorine residual in the tank.



I wouldn't worry about stripping some out when filtering from shore water. If you're not using a huge filter and slowing the flow way down, you're likely not removing anywhere near 100% of the chlorine anyway. As long as you shock the system every once in a while and keep things clean, it won't take much of a chlorine residual (you can test for this) to keep things clean and happy.