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Old 28-09-2011, 22:45   #16
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Re: Refilling Water Tanks

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Not only does it damage the system, but unless you add enough to make your water taste and smell like a laundry, it’s not enough to do any good. Even if it were, any “purifying” properties in chlorine evaporate within 24 hours, leaving behind only the corrosive properties.
This is so wrong. Not even sure where to start The reason chlorine is used almost universally in the water purification business is because it is the one disinfectant that has a long term effect. The hypochlorite ions that are present in chlorine bleach have a long lasting residual disinfection effect at concentrations as low as 0.1 to 0.2 parts per million. There are lots of reasons to not like chlorine, including the fact that overdosing your water with it can result in carcinogenic byproducts, but the health risks from dysentery far outweigh the risks from cancer. Metal tanks and other equipment are another question as well, and absolutely must be considered, but chlorine is a very valid method for water disinfection on our boats.

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Over the last 100 years in the United States, we've all but managed to forget that waterborne diseases have historically been a significant killer of humankind. For much of the rest of the world - including many areas that might be visited by cruising sailors - waterborne diseases are still a fact of life, and are estimated to be the cause of 4% of deaths worldwide. (For some fascinating reading on the subject, see www.who.int/peh/burden/ArticleEHP052002.pdf.)

The number one preventative measure is disinfection of the drinking water supply. There are three relatively common methods that are reasonably available to the cruising sailor: ultraviolet light, ozone treatment and chlorine treatment. All are capable of providing four nines - 99.99% - or better destruction of harmful pathogens.

I don't include the reverse osmosis watermaker process among the disinfection measures, for while it does provide physical removal of contaminants, it doesn't meet the traditional requirements of disinfection.

Of the three disinfection methods, only chlorine provides a lasting disinfection residual. UV light disinfection occurs in a chamber with a lamp that emits UV rays. This results in the death or destruction of most common pathogens. But there is no residual effect, meaning that as soon as the water comes out of the chamber, it is susceptible to recontamination. The same is essentially true of ozone, as any residual effect is short-lived. Both UV and ozone can be and are used to provide safe drinking water. The use of either UV or ozone requires that all piping, tankage, and appurtenances downstream of the water treatment system be maintained in a sterile condition. This is possible on a boat, but difficult.

All of the above also apply to reverse osmosis seawater from our watermakers. But with physical removal, we also have to worry about minute amounts of water bypassing the treatment process - say slightly leaky seals - and contaminating our storage tanks. How clean is the water you are putting into the watermaker? Middle ocean, probably no worries. In the anchorage, with some of your fellow cruisers who don't believe in holding tanks?

This is why various chlorine disinfection techniques are popular in the United States. There can be lots of discussion about cancer caused by chlorine disinfection and its breakdown products, and all of those points are valid. However, on a risk-adjusted basis, chlorine is the most forgiving disinfection option for the small water system because it can provide a residual effect that can last days or weeks. This means that downstream storage and distribution facilities need to be kept clean, but are kept sterile by the residual chlorine.

Assuming that most sailors use household sodium hypochlorite (NaOCl) bleach as their source of chlorine for disinfection, here are some numbers. Most bleach is about 5% NaOCl, or 50,000 parts per million. In liquid form, this disassociates to sodium ions (Na+) and hypochlorous (OCl-) ions. It is the latter that provide the disinfection power, and in standard bleach it is present at a concentration of about 34,500 ppm. The amount required for disinfection varies depending on the contamination burden in the water to be treated. Most guides generally recommend a dosage of about 10 ppm of OCl- to start with. This is equal to about one-third cup of household bleach per hundred gallons of water (20 milliliters per 100 liters).

After a brief contact time (half an hour+/-), if there is any remaining residual chlorine present, the disinfection is complete, and the water is safe to drink. If there is no residual chlorine, more must be added until a residual is detectable. In the water treatment business, we used to use 0.5 ppm residual as proof of disinfection. In reality, this value was based on that being the lowest level that could be reliably detected by testing. Current technology allows reliable detection down to about 0.1 ppm, and somewhere between these two values is now used to indicate complete disinfection. Where water is to be stored for an extended period, a higher value is used. When water is to be used immediately, a lower value is used. After all, the less chlorine used, the fewer the by-products - read carcinogens - that are generated.

For the cruising sailor, a cheap swimming pool test kit can allow you to test down to about 0.5 ppm - and provide confirmation of disinfection while minimizing chlorine use. For those who think they can keep everything clean, small treatment units using either UV or ozone treatment are available from a number of marine manufacturers. For those of us who use watermakers, UV, or ozone treatment, it is a good idea to disinfect the entire storage and distribution system at least once a year with a chlorine-based treatment. You want to make sure, of course, that none of the chlorine gets into the watermaker itself, as this can destroy the very expensive reverse osmosis membrane in short order. The water used for the disinfection can be discarded - preferably to a pump station, as residual chlorine can kill marine life if discharged to the ocean - and the user can return to drinking water disinfected by other methods.
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Old 29-09-2011, 05:00   #17
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Re: Refilling Water Tanks

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Originally Posted by Rakuflames View Post
I'm just going to point out that I typeset a textbook for dental hygienists some years ago. It very clearly made the point that nothing can be 100% sterilized. Microbes will get into tiny cracks and crevices and all the bleach in the world won't get into some of those tiny cracks and crevices. If you're going to drink this water, you might put a couple of drops of bleach in it and leave it out overnight.
Yes but you aren't drinking water out of the cracks. If the bleach makes it out of the facet into your glass it is safe to drink. This doesn't mean you don't have a biofilm growing somewhere.
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Old 29-09-2011, 05:09   #18
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Re: Refilling Water Tanks

As a professional water treater:

I added some bleach to my tank a few weeks ago and last week tested the water for free chlorine. And it was still in a good range for bilogical control. So the bleach doesn't just dissapear in a dark water tank in the couple of weeks.

If you are going to use bleach get yourself some measuring sticks from the local home store to test for it.

Water Filters = the largest biological breeding spot on our boat after the holding tank. If you are counting on just a filter to keep your water good you are just filtering your water though a biofilm. (I have a filter for drinking outlet that removes the chlorine).If your filter removes biological where do think think the bugs now are?
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Old 29-09-2011, 05:50   #19
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Re: Refilling Water Tanks

I have a stainless steel tank 75 gallons and all the plumbing is copper pipe.
I have no issues with growth that I can tell but have seen boats with plastic pipes when the water sits turns foul.

So is there anything the bugs can eat in my tank? I read that copper pipes are antimicrobial.

CDA Hails EPA Decision on Antimicrobial Copper Alloys

I wonder what s supporting growth of bacteria in a water tank at all. There must be dissolved organic contaminates which you drink and dont realize your drinking them right from the water source.
Perhaps filtering the water before going into the tank would help.
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Old 29-09-2011, 07:01   #20
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Re: Refilling Water Tanks

I wanted to add to my earlier post. I was reminded that I neglected to say where the information I posted came from. I had copied and pasted it a long time ago and had forgotten where I originally got it. This is from our own expert, Peggy Hall, and I have found her advise to be spot on over the years. Sorry Peggy for omitting that originally but won't forget in the future. Chuck
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