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Old 28-09-2011, 08:34   #1
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Refilling Water Tanks

My tanks are empty. I was planning on adding a cup of bleach to the tanks while refilling my 157 gal tanks. Is this recommended? Is there something else/better that I should do before refilling? Of course the goal is to have as good and safe potable water as possible. Thank You.

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Old 28-09-2011, 08:40   #2
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Re: Refilling Water Tanks

Here is a link I saved quite a while ago on sanitizing the water tanks in an RV. You might find it useful.

How to Sanitize Your RV Fresh Water System

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Old 28-09-2011, 08:52   #3
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Re: Refilling Water Tanks

Thank you very much Rich. The RV industry is great at stuff like this. I plan to follow their suggestion.
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Old 28-09-2011, 10:14   #4
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Re: Refilling Water Tanks

Boats and RVs are built different. Many boats have aluminum tanks which do not mix well with bleach, chlorine, or pool cleaning chemicals. Not to mention watermakers. If you have plastic tanks, an on demand pressure pump and no metal accumulator tank and of course no watermaker then bleach should be safe to use. But there are better ways to clean tanks. A good filter system should be on any boat, especially if the owner will consume water directly from the tanks, no matter how clean you think your tanks are.
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Old 28-09-2011, 11:30   #5
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Re: Refilling Water Tanks

Hi Tellie,

There are two tanks on my boat, one fiberglass and another plastic, no watermaker, and a plastic accumulator so I have no compunctions about using bleach. However, I do make sure that the hot water heater is not turned on until a thorough flush with fresh water. I do so to protect the heating elements.

I also agree with you about having a filter system. Mine is a simple activated charcoal filter that I got from Home Despot. I plumbed it in to the output end of the water pump. During the summer I change the filter every two or three months depending upon use. For drinking purposes I also use a Britta pitcher with filter that I keep in the fridge.

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Old 28-09-2011, 11:55   #6
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Re: Refilling Water Tanks

The US Red Cross recommends 1/4 teaspoon of unscented household bleach per gallon of water for purification purposes, which tanslates to about 2 Oz to a 50 gallon tank. We've used that as a rule of thumb but one's water may still "go bad" over an extended holding period. Some authorities suggest retreating water at monthly intervals although I've been somewhat reluctant to do that. A good activated charcoal filter will pull any chlorine "taste" out of the water.

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Old 28-09-2011, 12:15   #7

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Re: Refilling Water Tanks

Originally Posted by cabo_sailor View Post
Here is a link I saved quite a while ago on sanitizing the water tanks in an RV. You might find it useful.

How to Sanitize Your RV Fresh Water System


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.
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Old 28-09-2011, 16:54   #8
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Re: Refilling Water Tanks

We only add chemistry for washing the tanks, then fill with regular dock water. In most places the dock water is treated and we never got any health/smell/etc. issues.

If leaving the boat for any prolonged period, empty the tanks.

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Old 28-09-2011, 17:15   #9
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Re: Refilling Water Tanks

I worry more about the lead in most garden variety water hoses (on every dock), than I do about the water itself... Found a lead free, made for drinking, water hose for $10 at walmart in the RV supply section.
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Old 28-09-2011, 17:28   #10
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Re: Refilling Water Tanks

Here is the process we use for cleaning our tanks, it comes from the RV industry. We have been doing this for years and our tanks are in great shape and no odor or taste problems. You don't need to add bleach on a regular basis but you should clean the tanks annually. Chuck

Recommission the system at least annually

"This is all it takes to keep onboard water safe, and tasting/smelling as good as any that comes out of faucets on land: Fresh water system problems--foul odor or taste--are typically caused by allowing water to stagnate in the system. Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.” There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing.

The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles. The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated. Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete. Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded.

1. Prepare a chlorine solution using one gallon of water and 1/2 cup (4 oz) Clorox or Purex household bleach (5% sodium Hypochlorite solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity.
2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled. Do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines
3. Allow to stand for at least three hours, but no longer than 24 hours. 4. Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat.
5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vehicle motion.
6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable water.

People have expressed concern about using this method to recommission aluminum tanks. While bleach (chlorine) IS corrosive, it’s effects are cumulative. So the effect of an annual or semi-annual "shock treatment" is negligible compared to the cumulative effect of holding chlorinated city water in the tank for years. Nevertheless, it's a good idea to mix the total amount of bleach in a few gallons of water before putting it into either a stainless or aluminum tank. People have also expressed concern about the potential damage to rubber and neoprene water pump parts. Again—the cumulative effect of carrying chlorinated water is far more damaging over time than the occasional “shock treatment.” And it’s that cumulative effect that makes it a VERY bad idea to add a little bleach to each fill. 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.

An annual or semi-annual recommissioning according to the above directions is all that should be necessary to keep your water tasting and smelling as good as anything that comes out of any faucet on land. If you need to improve on that, install a water filter. Just remember that a filter is not a substitute for cleaning out the system, and that filters require regular inspection and cleaning or replacement. To keep the water system cleaner longer, use your fresh water...keep water flowing through system. The molds, fungi, and bacteria only start to grow in hoses that aren't being used.

Before filling the tank each time, always let the dock water run for at least 15 minutes first...the same critters that like the lines on your boat LOVE the dock supply line and your hose that sit in the warm sun, and you certainly don't want to transfer water that's been sitting in the dock supply line to your boat's system. So let the water run long enough to flush out all the water that's been standing in them so that what goes into your boat is coming straight from the water main.
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Old 28-09-2011, 18:44   #11
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Re: Refilling Water Tanks

I don't know how many boaters I have seen top off their water tanks with the hose at the holding tank pumpout.

Blech!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!
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Old 28-09-2011, 19:49   #12
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Re: Refilling Water Tanks

One little word on filters be they carbon or media. After an extended period of non-use (measured in 4-5 days not weeks BTW) its best to flush the filters by running the taps for a minute or two, before drinking. Turns out that the filters offer a great growth media for bacteria. Carbon especially.

That goes for household filters too BTW, including those used on ice makers. Go on vacation, Better to flush the filters for a few minutes.

I don't use drinking water filters on my boat, but just keep the tank turned over every few weeks with fresh. But then again I only have 35 gallons (So far), and liveaboard /cruise full time.

On a boat or RV that is not used that often, the filter at the tap can offer a high Bacteria colony count if it is not flushed out for a few minutes before use.

Don't even get me started on shower heads, You'll not like that answer either.

As someone said, even when clean and sanitized the water system has bacteria in all the little microscopic crevices etc.
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Old 28-09-2011, 20:10   #13
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Re: Refilling Water Tanks

Its not just the microscopic crevices that sequester the bacteria. As soon as you are finished flushing and commissioning the system, a "biofilm" starts to form on all internal surfaces. Once started it is extremely difficult to clean ...think like brushing the plaque off your kids teeth. The stuff is tenacious and bacteria laden. Rinsing frequently with anti bacterial cleansers is the only way to keep the "critters" at bay and hope to have a healthy system. Filtering at the end is a must.
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Old 28-09-2011, 20:53   #14
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Re: Refilling Water Tanks

We sell at lot of this stuff here in South Florida: Clean Tabs USA
The Puriclean is a system and tank cleaner, the Clean Tabs help keep drinking water fresh and clean.
Here's the British website for those on the wrong side of the Atlantic:
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Old 28-09-2011, 21:39   #15
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Re: Refilling Water Tanks

A problem with using a lot of bleach is that it will take many flushes of the tank to get rid of all of the bleach smell. Even filters have trouble getting strong chlorine concentrations out. Municipal water typically has between .5 and 1 parts per million chlorine. This is about 1.5 teaspoons of household beach per 100 gallons. Much above this level you can smell the chlorine.

The other problem with chlorine is that it loses it's disinfecting power after about 24 hours of exposure to air (as in a water tank with a vent). Even sealed in a jug, bleach loses strength quickly. Don't use bleach that's over 6 months old.

The best thing to do is use the water. I try very hard to not let water sit more than two weeks in a tank. If it has, I'll add bleach at the rate of a cap per 100 gallons. I also empty a tank all the way before filling. Once a year I do the disinfecting thing as discussed above and spend a couple of days flushing.

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