Seawater into freshwater tank via thru-hull overflow tube

C

Cschwankl

New member
My first post as an official C-Brat!

My wife and I recently purchased a 23' Venture. When we winterized her we noticed that the fresh water tank had what appears to be mold or algal contamination. I believe it's due to outside seawater and/or rain streaming into the freshwater tank from the thru-hull overfill/air tube.

My questionn is, how do I prevent this problem?

Ideally I'd like to install some sort of device that will allow water out of the line but completely prevent water from coming in. Even if such a thing existed, it might cause vacuum suction problems when I turn on the water pump because it would then be a sealed system not allowing air in.

I'm considering just plugging the hole through the hull and not having any sort of overfill tube, leaving the top opening open to still allow air in. It's a 20 gal tank and I'd like to get in the habit of only filling it with 10 gal so that at the end of a weekend I can empty the rest and always fill with fresh water before starting a trip. If I happen to really screw up and overfill there is a bilge pump right near the base of the water tank.

For now I've removed the tank and I'm going to clean it by filling it with 10% bleach solution.

Any information or suggestions on how to prevent this problem would be greatly appreciated!

Chris
Fish Hawk
 
Cschwankl":39hz0tes said:
My first post as an official C-Brat!

My wife and I recently purchased a 23' Venture. When we winterized her we noticed that the fresh water tank had what appears to be mold or algal contamination. I believe it's due to outside seawater and/or rain streaming into the freshwater tank from the thru-hull overfill/air tube.

My questionn is, how do I prevent this problem?

Ideally I'd like to install some sort of device that will allow water out of the line but completely prevent water from coming in. Even if such a thing existed, it might cause vacuum suction problems when I turn on the water pump because it would then be a sealed system not allowing air in.

I'm considering just plugging the hole through the hull and not having any sort of overfill tube, leaving the top opening open to still allow air in. It's a 20 gal tank and I'd like to get in the habit of only filling it with 10 gal so that at the end of a weekend I can empty the rest and always fill with fresh water before starting a trip. If I happen to really screw up and overfill there is a bilge pump right near the base of the water tank.

For now I've removed the tank and I'm going to clean it by filling it with 10% bleach solution.

Any information or suggestions on how to prevent this problem would be greatly appreciated!

Chris
Fish Hawk
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I rather doubt it is due to contamination from the outside sources. Every fresh water tank will eventually get some mold or algae. You pretty much have to empty it every now and then and add some bleach water. 10% is a bit high. 1% is plenty if left in contact with the tank for 20-30 mins.
 
Bleach works, but you might look into hydrogen peroxide. Bleach actually has kind of a short shelf life for use as a disinfectant. Just because it stinks doesn't mean that it's still potent. Check out this comparison site.

http://www.education.nh.gov/instruction ... ctants.pdf

Hydrogen peroxide doesn't have the potential for liver and kidney damage, etc. Buy a quart and use the whole thing, as it also has a shelf life. No odor and if left long enough in the tank, you don't even have to rinse (but I sure would because it is likely to "fizz" off the scum that you can see through the tank).

Mark
 
Mark,

Are you saying you could just put in a quart of Hydrogen Peroxide into the tank, (I'm thinking the House System water to the sink tank) and leave it in there, fill the tank with the 15 gallons and then use that water as you go? (If you are not drinking it or cooking with it.)

Because I don't use much of that water, washing me and dishes mostly I have just left a small amount of bleach in the tank to keep it from getting "green things":shock: in it. Helps to keep my hair blonde 8) too :lol:

Harvey
SleepyC :moon

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Harvey,

Hydrogen peroxide will also make you blonde (hence the term "peroxide blonde"), but unlike bleach it quickly dissipates in most conditions. A quart to 15 gallons would definitely sterilize the tank. At our cabin, I use one cup to approx 100 gallons in my wood fired hot tub (actually a cattle water trough). After one hour, the peroxide has flashed off and the water (which comes from a spring) is fine for use. That's in part because H2O2 decomposes after reacting with any contaminants and by the rising temperature in the tub. No bleaching effect, no smell, no irritation, but I'm not sure that I would drink the water. :beer

Mark
 
Thanks Mark,

(BTW Cool house stuff.)

The OP mentions water possible water intrusion via the overflow tube.
"I believe it's due to outside seawater and/or rain streaming into the freshwater tank from the thru-hull overfill/air tube." This had me thinking of a live well type tank, not the house system tank. I'm not sure how that system works on the 23, but on the 22, the vent tube is inside the cabin. Not likely to get Salt Water or rain into that one.

I don't think I would want SW access to my fresh water system tank.

Harvey
SleepyC:moon

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I'm talking about the house water tank that supplies water to the sink. On my 23 Venture the tank has an overflow tube from the top of the tank through the hull to the exterior. Presumably designed that way so that you could never spill water into the boat by overfilling the tank and to prevent the electric sink pump from creating a vacuum inside the tank. It's a flawed design though because it definitely allows seawater and/or rainwater to stream into the tube and in the tank as water slides down/alongside the hull while under way - especially in heavy seas. I'm probably going to plug the hole through the hull, get rid of the overflow tube, and just be careful to not fill the tank more than 2/3 full. I gather hardly anyone uses the sink water for anything except washing dishes and hands, but I'll clean the tank with H2O2 or a low concentration of bleach and scrub the inside of the tank with a flexible long handled brush so it's nice and clean anyway. Or at least that's the plan for now. Thanks for the info.
 
I have been a Washington State Department of Health Certified Water Distribution manager for many years. I have no knowledge of using hydrogen peroxide for decontamination or purification of a water system. This is how the water main that serves your home is treated when new pipes are installed during construction and also in the case of a distribution system being contaminated. The pipe and/or reservoir is super chlorinated at approximately 50 parts per million of 10% sodium hypochlorite (Clorox is 6%). It is then required to soak for 48 hours. It is then flushed thoroughly before bacteria samples are taken. once these samples pass the test the system is put in to use. If the samples fail the process is repeated. It is very seldom that if the process is done right it does not pass on the first attempt. This is how the water distribution system that serves your home is treated and I have full confidence it will work on your c-dory. I super chlorinate and then thoroughly flush ours at the start of the season and I have no problem drinking water out of the tank after that. If water is left stagnant in a tank for a long period of time without chlorination bacteria will start to grow. It is not always harmful even if it looks nasty, but best to kill it off all the same.

Doug
 
My wife beat me to the punch and cleaned the tank without me knowing it. She used 10% bleach for two days. I then dumped the bleach solution and flushed thoroughly with fresh water. The tank is now sparkling clean and ready to be reinstalled.
 
Cschwankl, The "vent tube" in the 22's is a clear vinyl tube with the top well above the level of the fill port on the gunnel. It is inside and I put a bit of gauze over the end to discourage 6 or 8 legged visitors. Also allows for visual inspection of tank fill level and clear water.

Doug, Thanks for that explanation. It sounds like my bleach treatment of the system is OK then, and I may continue as planned. It has worked before. I do leave a bit of bleach in the system to discourage the green stuff because I don't empty the tank each trip.

Harvey
SleepyC :moon

JC_Lately_SleepyC_Flat_Blue_070.thumb.jpg
 
I am also thinking of installing a plug or sea cock in my thru-hull when not in use or if I'm moored overnight. My thru-hull location is only about 4 inches above the top of the "bottom paint" line. I really wish I had went a few inches higher but that's not worth complaining about now. I don't think it's possible for water to "intrude" because the drain hose is almost vertical that goes to my sink....but better safe than sorry.

Any ideas? A plug would be great but not while in the water.....A seacock seems like the way to go but they only come pre-assembled with the thru hull, right?

Or should I just forget about it and enjoy the boat!? HAHA
 
Chloramine is used in some water systems .
see
http://www.cdc.gov/healthywater/drinkin ... ction.html


Back to the Q
Excellent advice from everyone.

Sometimes multiple treatments to thoroughly clean your water tank may be needed. Most likely there is a biofilm present and difficult to remove and additional treatments may be required and cant give the tank inside a good scrubbing. Personally I like hot water with a little bleach, lots of agitation and soak time,

BTW we used vaporized hydrogen peroxide in our labs in case of major accident or agent release
see
https://www.steris.com/products/vaporiz ... sterilizer

HVP was used mail facilities and federal government buildings
one article
http://2001-2009.state.gov/r/pa/prs/ps/2003/18992.htm
 
It is usually the same style of vent as the fuel tank vent. Like that vent, the line to it needs to have a nice big loop that goes up as high as you can get it above the tank fill line, preferably right at the point of attachment to the vent. That way, a big wave pounding into the vent will not be able to squirt water up and into the tank. You also don't want a low spot in the line. That creates a "P trap" situation that will suck water out of the trap area and into the tank as the water is used.

I'm surprised that the C Dory freshwater tanks vent through the hull. Worst case scenario, the tank is overfilled and a little squirt of freshwater gets on the fiberglass. That doesn't justify a hole in the hull for me. I don't think I've ever had a boat with an overboard freshwater vent.

Mark
 
I always fill my water tank to the limit when going on a longer trip. Never had a problem that I am aware of. Like someone else mentioned, I don't know anyone who drinks direct from the tank. I use it for washing the dishes, washing my hands, or a strip bath. For drinking, I carry a 5 gal portable or a case of bottled water.
I did get a contaminated tank once from using an old hose that had been laying around. A cup of bleach to a tank fill up, let sit overnight then flush, sorted it out. I did do this flush twice.

Martin.
 
Harvey, If I understand correctly you say that the "vent tube" for the C Dory 22 water tank is inside of the cabin. All of the C dory's I have owned, including two 22's have the water overflow on the outside of the hull. There is a "Water level" tube on the inside of the cabin,. but that is not a vent tube.

Cschwankl how are you going to vent the tank, if you don't have the outside overflow? We have never detected any salt water contamination of our water tanks, in any of the small boats we have owned except when we were sailing across the Atlantic and the water tank vent was under water as we were heeled over for prolonged time at over 45 degrees and we used water out of that tank, creating a vacuum to pull in salt water!) I later re-routed the vent to the side of the pilot house, from the side of the hull)

Marco, The links is for "EPA registered (food contact) Hard surface" wipe down.
http://www.education.nh.gov/instruction ... ctants.pdf

Not for water tanks. EPA continues to recommend 50 PPM using 8.25% or 5.25% sodium hypochlorite bleach for decontamination. Let sit--We usually use 6 hours, but up to 48 hours, and then rinse several times, until there is no further Cl smell.
Table for using 5.25% bleach (non scented):
For treating unknown clear water: Double for cloudy water.
Approximate measurements:
8 drops per gallon: i drop = 0.017 oz (about 5 ppm)
For 10 gallons a Teaspoon (0.16 oz)~5 ppm, 3 teaspoons=50 ppm
for 25 gallons, 1/2 Tablespoon (0..25 oz) = 5 ppm, 4oz = 50 ppm (Tablespoon = 0.25 oz


We drink water out of our water tanks. (This is why we can go 10 days at Powell with the 20 gallon tank, and a back up of 5 gallon in a plastic container.) Marie dose use the Brita filter. I don't care if it is filtered or not.

We do use 8.25% of sodium hypochlorite at the end of season, and pump the line dry. Before a trip, we usually flush the tank with a 50 PPM solution. (put in about half water, then add the bleach, then the rest of the water.

EPA:
The EPA requires treated tap water to have a detectable level of chlorine to help prevent contamination. The allowable chlorine levels in drinking water (up to 4 parts per million) pose “no known or expected health risk [including] an adequate margin of safety.” Only chlorine based disinfectants can provide lasting protection from waterborne diseases throughout the distribution system from treatment plant to the consumer’s tap.
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Most home water contains about 1 ppm of chlorine.

H2O2 comes in many concentrations. Usually drug store starts out at 3% or 6%. When H2O2 is used in waste water decontamination it is higher concentration or 50% or so (not stable, and requires specialized handling). Although you might use H2O2 to clean surfaces, I would not recommend it for regular use as treatment. The contact time and concentration will not be adequate.

Here is EPA's take:
Hydrogen peroxide (H2O2) is rarely used in drinking water treatment as a stand-alone treatment process. H2O2 is a weak mirobiocide compared to chlorine, ozone, and other commonly used disinfectants. Consequently, it is not approved by regulatory agencies as a stand-alone disinfection treatment process. However, there are a number of technologies where H2O2 is used as part of the treatment program. The advanced oxidation process (AOP) uses H2O2 in conjunction of O3 and/or UV light to produce hydroxyl radicals (·OH), which are very effective in removing taste and odor (T&O) compounds, and inorganic and organic micropollutants. H2O2 can also be catalyzed with iron, to produce hydroxyl radicals by Fenton's reaction. Addition of H2O2 in conjunction of UV light and/or ozone produces powerful hydroxyl radicals, which are more effective than ozone or UV alone. AOP involving hydroxyl radicals in drinking water treatment is used to remove various persistent organic and inorganic micro-pollutants. O3/ H2O2 and UV/ H2O2 have been successfully used to oxidize many persistent pesticides, T&O compounds, pharmaceutical and hazardous chemicals that may be present in surface and groundwater.
In the Fenton process, H2O2 and iron generate hydroxyl radicals through a catalytic process. The process is based on electron transfer between H2O2 and iron ions. The hydroxyl radical produced during this activation process is a strong oxidizing agent able to oxidize organic compounds. The advantage of this process is that no energy input is necessary to activate the hydrogen peroxide. However, the main disadvantage of this process is the additional water pollution caused by adding the iron salt. Solid iron blocks have been used to avoid water pollution with iron salt; however, leaching of metal ions makes this process problematic. Fenton's Reagent has proven to be very effective in the treatment of organic molecules. However, the process is expensive because additional residuals, which require disposal, are generated and a continuous supply of feed chemicals is required."
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I've also always drunk out of the onboard water tanks (on various boats). There wouldn't really be any other practical way to do it when cruising (previous boats). If I had a tank that I didn't feel I could clean and sanitize, I would modify it or even get a different one (add cleanout port, etc.)

Also helps to cut down on plastic trash (small disposable water bottles), which is not always easy to store or get rid of when underway (and I prefer to minimize it in any case).

Obviously if you can't take on potable water, then drinking out of the tank is a no-no. But I still like to have the convenience of being able to drink out of the tank, if desired.

On the other hand, I helped a friend to put a "day tank" into his RV. Reason was, water you can get to fill a large RV water tank in the southwest (for example at state parks and other campgrounds) is often VERY hard, but you can easily buy water by the gallon. So now he can fill the three gallon day tank (with separate hand pump at sink) with drinking water and then the ~50 gallon main tank with the harder water. Not that it's not potable, but just not very desirable. The day tank ended up being easier than finding places to store and set (on the counter) individual gallons.
 
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