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Old 30-07-2004, 13:36   #1
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Fresh water tank treatment

I understand that we should be adding bleach to our freash water tanks. How much bleach is recomended for 100 gals? How long will it be effective?
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Old 31-07-2004, 03:32   #2
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1 tsp of bleach for every 15 gallons of water .... then leave the fill cap removed for 30 minutes before replacing it. This is one of those situations where more is not better.

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Old 31-07-2004, 03:42   #3
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It's not that simple ...

Irwinsailor:
Your (apparently simple) query doesn’t really have a simple answer. There are a number of factors that can effect the proper chlorine dosage.

Read some excellent on-line advice on water treatment (disinfection):

USCG - POTABLE WATER TANK DISINFECTION PROCEDURES
http://www.uscg.mil/mlclant/KDiv/kseMSGPotH20.htm

US-EPA - Emergency Disinfection of Drinking Water
http://www.epa.gov/safewater/faq/emerg.html

Food & Water Precautions, Water Treatment by Janette Loomis, RN, BS, Meridian Passage and James H. Bryan, MD, PhD
from: The Healthy Cruisers Handbook, Prevention and Treatment Medical Resource Guide.
http://www.clubcruceros.org/FoodWaterPrecautions.html

Chlorination of Drinking Water by Linda Wagenet and Ann Lemley
from: Cornell Cooperative Extension, New York State College of Human Ecology
http://www.cce.cornell.edu/factsheet...eets/fact5.htm

From Peggy Hall (“The Head Mistress”), author of “Get Rid of Boat Odors”
A guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor.
http://shop.sailboatowners.com/detai...=400&group=327

Turn water heater off at the breaker before beginning. Do not turn it on again until entire recommissioning is complete.
1. Prepare a chlorine solution using one gallon of water and 1/2 cup Clorox or Purex household bleach (5% sodium Hypochlorine solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity, which results in 4 Ounces of bleach for 10 gallons of water.
2. Complete filling of tank with fresh water. Turn on every faucet and allow water to run until what's coming out smells strongly of bleach.
3. Turn off faucets--but do NOT turn off the pump...it must remain on to keep the system pressurized so that the solution remains in the lines. Allow to stand for at least 3 hours, but no longer than 24 hours.
4. Drain the tank through every faucet.
5. Refill tank with clean fresh water and drain again through every faucet.
6. 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 (iow, go sailing and tack a lot).
7. Drain tank again through every faucet, and refill with potable water.

The above 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.
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Old 31-07-2004, 04:56   #4
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From the US Navy

From Department of the Navy - Manual of Naval Preventive Medicine:
Chapter 6: Water Supply Afloat:

Chlorine Dosage Calculator
http://www.vnh.org/PreventiveMedicin...ter6/6.25.html

Disinfection of Potable Water Hoses and Appurtenances
http://www.vnh.org/PreventiveMedicin...ter6/6.23.html

Emergency Disinfection of Water for Drinking and Cooling Purposes
http://www.vnh.org/PreventiveMedicin...ter6/6.24.html

Required Halogen Residuals
http://www.vnh.org/PreventiveMedicin...ter6/6.26.html


Chlorine readily combines with chemicals dissolved in water, microorganisms, small animals, plant material, tastes, odors, and colors. These components "use up" chlorine and comprise the chlorine demand of the treatment system. It is important to add sufficient chlorine to the water to meet the chlorine demand and provide residual disinfection. The chlorinated water should retain a slight chlorine taste and odour.

The chlorine that does not combine with other components in the water is free (residual) chlorine, and the breakpoint is the point at which free chlorine is available for continuous disinfection. An ideal system supplies free chlorine at a concentration of 0.3-0.5 mg/l. Simple test kits, most commonly the DPD calorimetric test kit (so called because diethyl phenylene diamine produces the color reaction), are available for testing breakpoint and chlorine residual in private systems. The kit must test free chlorine, not total chlorine.

The contact (retention) time in chlorination is that period between introduction of the disinfectant and when the water is used. A long interaction between chlorine and the microorganisms results in an effective disinfection process. Contact time varies with chlorine concentration, the type of pathogens present, pH, and temperature of the water. Contact time must increase under conditions of low water temperature or high pH (alkalinity). Complete mixing of chlorine and water is necessary.

If a system does not allow adequate contact time with normal dosages of chlorine, superchlorination followed by dechlorination (chlorine removal) may be necessary.

To treat 100 Gallons of water (standard chlorination):

5.25% Sodium Hypochlorite - Household Bleach
Contact Time -vs- 5.25% Chlorine Concentration:
2 Hours - 100 ppm (about 3 Cups or 26 ounces Bleach for 100 Gallons Water)
8 Hours - 50 ppm (about 1.5 cup or 13 oz. per 100 gal.)
24 Hours 25 ppm (about 3/4 cup or 7 oz. for 100 gal.)

65% Granular Calcium Hypochlorite Powder - HTH, Perchloron, or Pittchlor
Contact Time -vs- 65% Chlorine Concentration:
2 Hrs - 100 ppm (2 ounces per 100 gal.)
8 Hrs - 50 ppm (1 oz per 100 gal.)
24 Hrs - 25 ppm (˝ oz. per 100 gal.)

Minimum Halogen Residuals:
Standard: 0.2 ppm chlorine after 30 minutes in tanks
Disinfection: 100 ppm chlorine initially, then 50 ppm after 4 hours in tanks

Superchlorination provides a chlorine residual of 10 times the recommended minimum breakpoint chlorine concentration. Retention time for superchlorination is approximately 5 minutes. Activated carbon filtration removes the high chlorine residual.

Shock chlorination, at about 4 times the recommended minimum breakpoint chlorine concentration, is recommended whenever a tank is new, repaired, or found to be contaminated. This treatment introduces high levels of chlorine to the water. Unlike superchlorination, shock chlorination is a "one time only" occurrence, and chlorine is depleted as water flows through the system; activated carbon treatment is not required. If bacteriological problems persist following shock chlorination, a continuous chlorination system should be used.

Potable water tanks, pumps, hoses, & fittings are disinfected by filling with a solution containing not less than 100 ppm FAC. The solution must be in contact with the entire internal surface of the system for not less than two minutes. Flush the system 30 to 60 seconds with potable water prior to use.














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Old 31-07-2004, 11:30   #5
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Thanks for all the info Mr. Gord.

The above inspired me to go and "do" my tank this morning:

Surfed all the tables and came up with a "good slug" as the measured amount of 10% chlorine to super-shock my 157 gallon fresh water tank.

During the long cruise we did this summer, I probably did not add enough chlorine to the tank, as the rotten egg smell started appearing after about 18 days or so.
It was still potable as the ships drinking water is being filtered through a farily big cartridge..On this trip is was brand new.
Normally I change it once a year or so.

At any rate, now letting the super chlorinated water sit in the tanks and in the hoses / filters for a few hours, then going to drain it in the bilge, then pump it out using all of the 4 bilge pumps...So all the pumps and hoses and valves, etc get a good cleaning as well.

Probably should run some fresh water through all the systems as chlorine is quite corrosive and could cause long term damage in pumps, accumulators, valves and such......?

Thanks again for posting all that stuff.

D
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Old 31-07-2004, 17:34   #6
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Some excellent reading here. I think it important to add though, just for safety sake, that the general usage of "common household bleach" should be read with caution. Some general household bleachs hold other things such as Surfactants. You may not be adding "pure" chlorine to your water. Although the surfactants may or may not be harmfaul, you just never know and I don't really want to drink to many ummmm, "impurities".
Another chemical and one that I use personnaly is Hydrogen Peroxide. It is tastless and once it has reacted to any impurity in the tank, it turns back to water.
Both Chlorine and Peroxide are dangerouse in their concentrated form. So great caution is required in handling either. Chlorine can react violently with other chemicals and create highly toxic fumes in large quanitites and peroxide is a very potent oxidizer and will react violently with other chemicals and some metals.
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Old 31-07-2004, 19:34   #7
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Wow .... guess I'm not into such scientific research on what is basically a simple problem. While you're reading all of the technical information ... you might want to look into the technically legal aspects as well. Chlorine bleach is lethal to virtually all marine life, and it's discharge into the surrounding water is illegal .. in certain concentrations. This is to say nothing about the ethical ramifications. Call me a poor 'ole boy who dosen't read a lot of scientific literature ... but I know first hand that 1 tsp per every 15 gallons will kill every living thing in the water .. still be potable ..... legal & ethical.

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Old 04-08-2004, 05:19   #8
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More Basic

I gave a more basic overview of chlorine use under:

Cruisers Forum > Blue Water Cruising > The Galley > How Often & How Do You Do It

I do recommend you visit that thread as well.

As for the harm, you may be a little alarmist, but do raise a point worthy of consideration.

Chlorinated water does us little harm at concentrations below 1 ppm, but it can harm fish rather easily. The difference is that we simply ingest it into our gut, where it mixes and gets used up quickly with all the organics in there. Fish, however, have it contacting their gills, where it not only replaces the oxygen in the blood uptake, but actually damages the gills.

Can chlorine levels below 1 ppm hurt fish? Frankly, I believe that the small concentrations that leave a boat become diluted rather quickly, and get used up in the organics of surface water rather quickly. However, I certainly keep the risk in mind. Releasing large volumes of chlorinated water is wrong. We should do any shocking of tanks and pipes before we launch, and release strong solutions on the ground. If we have to do it afloat, capturing the water and allowing it to stand in sunlight will slowly dissipate the chlorine over time.

I also recommend using testers, and limiting the strength of solutions to what is necessary. People don't realize that household bleach can often have up to 50 000 parts per million of active chlorine (5%), where even a shocking solution shouldn't be stronger than 50 parts per million, and 0.5 parts per million is fine for regular maintenance of our tanks. I would bet it is our overzealousness with this strong product that causes the damage, not proper use of the product.
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Old 04-08-2004, 18:27   #9
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I agree in principal with everything you have said ... but would bring up a couple of points. Who among us really thinks to test for chlorine levels in what we release? Here in SW FL, where we get lots of mold & mildew due to high temps & humidity .. we splash the stuff around like it's nothing. Had a chap ask me to find o-rings compatible with chlorine ( he carried it in a tanker truck) .... that's when I found out just how nasty the stuff really is.There is ancedotal evidence that the sudden appearance of chlorine bleach in household products, is directly linked to the sudden increase in breast cancer in this country ... I'm no scientist, but it wouldn't surprise me. From my standpoint, when cleaning mold from the exterior of the boat, I use oxalic acid, 100% organic ... very effective & water nuetralized. I do use bleach in my water tanks ... uh ... one tsp per 15 gallons (no idea what that works out to in PPM) .... and I use a large charcoal filter for the water before it comes out the tap! I truly don't know what the PPM allowance is for discharge ... but that's not really my point ... the point is, high concentrations are not a good idea, specially if a low concentration will do the job.

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Old 04-08-2004, 18:32   #10
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the point is, high concentrations are not a good idea, specially if a low concentration will do the job.
No arguement here.
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Old 23-03-2011, 11:19   #11
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Re: Fresh water tank treatment

When do you know you need to treat your tanks and water? Is there a test, time frame or rule of thumb? I don't want to fix anything that's not broken.
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