Watermakers vs Aluminum water tanks

[MV Wanderlust]

Good Afternoon,

Wondering if you guys and gals might be able weigh in on something. We are considering adding a watermaker to our 42' Chris Craft aft cabin.
We have a 170 gallon aluminum water tank and were thinking of looking around for a used watermaker capable of 20-30 gallons per hour.

I mentioned this to a mechanic the other day and he told me something surprising. He said desalinators don't remove all the salt from seawater; they just remove enough that you don't taste it any longer. He went on to say that there is still enough residual salt in the output water that it should not be pumped into an aluminum water tank because the salt will react with the aluminum and cause a dangerous corrosion.

This is the first I've ever heard of such a thing but I know there are plenty of people on this board who have watermakers or are engineers or are more experienced with these things than I and even a couple of people who own or work for companies that make watermakers. Any truth to this? Any issues we should be aware of?

Thanks.

John

[Sailmonkey]

You get more tds from some well water then you get from a properly functioning water maker.

Our little toy watermaker was usually less than 200 ppm tds. Bigger water makers usually can achieve better.

[belizesailor]

Hopefully your mechanic is a better mechanic than watermaker tech...

A properly function water meter produces water with very low total dissolved solids (TDS)...no problem putting it in an alumn tank.

[SV THIRD DAY]

Hey John
The mechanic you spoke to may be good with engine and transmissions, but his knowledge of marine RO water makers is a bit off. The TDS of sea water is about 32,000ppm. The TDS of typical RO water made from sea water ranges from 120ppm-500ppm. Hose tap water from around the Country is in the same range. So there is absolutely Zero Risk in putting Desal water into your aluminum water tanks from a corrosion standpoint. Now what IS a RISK is chlorinating your tanks or adding some type of oxidant. That can cause corrosion.

If Desal only removed sale down to the "you can taste it point" that would be about 1300ppm to 1500ppm. People's taste buds are a bit different, but that's why you NEVER want to rely on just Taste to see if your RO Desal unit is working right. You Always want to use a TDS meter or you could be drinking water with a high TDS content and that could be hard on your Kidneys.

I was in Mexico and a couple told me that their cat wouldn't drink their water maker water and that their herb garden was shriveling. They didn't have a TDS meter and were going by Taste. Well I gave them my spare TDS meter when I found out they had been drinking 1475TDS water for YEARS....ahhhh.....

Cheers

[MV Wanderlust]

Originally Posted by SV THIRD DAY

Now what IS a RISK is chlorinating your tanks or adding some type of oxidant.

Interesting! Thanks, Rich.

Spin off question... Do most people just pump the desalinated water into their fresh water tank and then drink it or do most people put in some additive to chlorinate it? Never heard of anyone specifically mentioning that they added chlorine or anything.

[Sailmonkey]

Originally Posted by JohnEasley

Interesting! Thanks, Rich.



Spin off question... Do most people just pump the desalinated water into their fresh water tank and then drink it or do most people put in some additive to chlorinate it? Never heard of anyone specifically mentioning that they added chlorine or anything.

We don't do anything to ours. Straight to the tank and then the mouth. One of the primary reasons we bought a desalination unit was to have good drinking water.

[SV THIRD DAY]

Originally Posted by JohnEasley

Interesting! Thanks, Rich.

Spin off question... Do most people just pump the desalinated water into their fresh water tank and then drink it or do most people put in some additive to chlorinate it? Never heard of anyone specifically mentioning that they added chlorine or anything.

When it comes to cruisers it's hard sometimes to say what most people do because there are 4 opinions on if it's night or day...ha ha ha

But the problem is once you start cruising out of the USA where they do not chlorinate the water and you are only putting RO water maker water into your tank, no matter how perfectly clean your water maker water is, the water can taste "pondy" after 6 months to a year. (or at least it does on our boat with SS tanks) So "some" people usually add some bleach or other tank cleaner at some interval to keep their tanks clean.

((Folks with AL tanks can't use bleach))

We chlorinate our tanks about every 6-8 months or when my wife complains about it. We use 1/4 cup of bleach per 50 gallons of water and have SS tanks. We just then don't do a water maker fresh water flush for 2 weeks after adding any chlorine. (it off gasses and goes away)

We also use a standard AC filter following our ships pressure pump so that all the faucts on the boat have the AC filter. At first we only did the galley sink, but then my wife would complain about brushing her teeth in the head. Having 450gals of water tankage in 4 tanks also means that our water sits around longer than folks with 75 or 120 gallon tanks. But we also use water like....well like water and don't think much about water conservation....

The theme here is that if the Wife isn't happy....no one is happy.

[MV Wanderlust]

Originally Posted by SV THIRD DAY

no matter how perfectly clean your water maker water is, the water can taste "pondy" after 6 months to a year.

((Folks with AL tanks can't use bleach))

The theme here is that if the Wife isn't happy....no one is happy.

Yeah, I'll buy that last part.

We have an aluminum 170 gal tank. We're pretty good about conservation, for the most part, but can drain it down in a week. If we install a water maker, there might be less of a tendency to conserve. I'm thinking ours probably won't sit around long enough to get "pondy."

If we install a water maker and it starts to taste funny, we'll look around for an additive that isn't harmful to aluminum.

Thanks for everyone's thoughts.

[belizesailor]

Originally Posted by SV THIRD DAY

Hey John
The mechanic you spoke to may be good with engine and transmissions, but his knowledge of marine RO water makers is a bit off. The TDS of sea water is about 32,000ppm. The TDS of typical RO water made from sea water ranges from 120ppm-500ppm. Hose tap water from around the Country is in the same range. So there is absolutely Zero Risk in putting Desal water into your aluminum water tanks from a corrosion standpoint. Now what IS a RISK is chlorinating your tanks or adding some type of oxidant. That can cause corrosion.

If Desal only removed sale down to the "you can taste it point" that would be about 1300ppm to 1500ppm. People's taste buds are a bit different, but that's why you NEVER want to rely on just Taste to see if your RO Desal unit is working right. You Always want to use a TDS meter or you could be drinking water with a high TDS content and that could be hard on your Kidneys.

I was in Mexico and a couple told me that their cat wouldn't drink their water maker water and that their herb garden was shriveling. They didn't have a TDS meter and were going by Taste. Well I gave them my spare TDS meter when I found out they had been drinking 1475TDS water for YEARS....ahhhh.....

Cheers

Wow, 1,475...those folks had no taste buds!

When working on the water maker I use a TDS meter for the final test...and in preparation for the ultimate test...the Admiral. Her palate is at least as sensitive as a good TDS meter. Now if I could just figure out how to calibrate her! 😆

[hellosailor]

John-
Don't even THINK about chlorine in an aluminum water tank. The tank will be ruined.

There are other chemicals you can use, when you must.

[a64pilot]

I have only seen one other chemical, and I'm suspicious of it as it's an Oxygenator.
In theory H2O2 ought to be able to be used, but I cannot find a concentration that is effective.
I filter every drop that goes into my tank through a carbon block filter at a low flow rate so far, and will soon have a watermaker. I find if I turn the tank weekly it has no issues (157 gl)

[HopCar]

If you are worried about damaging your aluminum water tank with bleach, try this:
Clean Tabs Ltd | Water Purification | Water Purification Tablets | Water Tank Cleaning | Water Treatment | Drinking Water Disinfection

It won't damage aluminum and is a very effective tank cleaner or water purifier.
I don't know if it's available in the USA anymore. I was the distributor but I understand the guys who bought my company haven't reordered it.

[topmast]

I'd be a tad more worried about the dissolved aluminium than a bit of salt. Probably more salt in a slice of bread. Aluminium is found in brain plaques in Allshimmers patients. Forget where I read this, but Epoxyied my tanks and never looked back

[thinwater]

There is a lot of semi-chemistry being tossed about on this thread.

• Chloride and TDS are very different from a corrosion standpoint. Typical boat RO water is 100-200 ppm chloride. For comparison, 25 ppm is the condemning limit for chloride in engine coolant, but that is hot and radiators are thin. On the other hand, disolved oxygen in an engine is virtually zero but will be nead saturation in a freshwater tank (6 ppm). There will be pitting, but the extent depends on the alloy.
• Chlorine is different than chloride. The RO will remove all of the city chloride, but unless you re-chlorinate, the water tank will get nasty. Yes, Clean Tabs are much better for aluminum (they've been tested for aluminum corrosion by Practical Sailor mag). With RO water you will be able to use very low, occasional chlorine doses.
• H2O2 has no accepted protocol as a water purification agent because WHO and EPA have determined it is not effective at any safe level. Using H2O2 in aluminum water tanks is legend.

Would I use the tank for RO water if it were my boat? Not if I was planning to keep the boat for a long time. Aluminum is a real sucker for pitting corrosion, and it can go fast once it starts. And why do I need to store that much RO water? Use a smaller tank and make it as you need it. It will be fresher that way. But the risk of corrosion is relatively low.... just not zero.

[hellosailor]

Hopcar-
Puriclean's MSDS seems to reveal very little aside from having an unspecified chlorine-based agent in it. It may just be an alternative to chlorine bleach, but still chlorine.

This won't be of use in filled tanks, but IIRC it is potassium sulfide (not sulfate) that is used in photography and as a sterilizing wash in brewing. Supposedly it will sterilize things and leave no contaminants, which is why hoe brewers use it to clean out containers. (The EPA got all bent out of shape over that, they classed it as a pesticide or something, but finally allowed the use.)

There are assorted iodine tablets and halazone (troclosine sodium) and other things out there, none close to the price of bleach, which is still the go-to chemical in most of the world. The aluminum tank is the problematic part if you need to "nuke" a water storage tank. But then again...I once left a (good brand) aluminum camping pot full of "spaghetti water" in the sink overnight and came back to find pinholes in it the next day. Kinda lost my love for aluminum since then. ("But it was the very best of butter!")

I can't help thinking that a good UV-C light in the tank would sterilize it, and that it would be able to do that adequately without needing to run all the time. Maybe we could get Practical Sailor to bankroll some testing.(G)