Deionized Water
Deionized Water
(OP)
It is my understanding that DI water at 18 megaohm is pure H2O. Can someone explain to me why when DI travels through cast iron pipe that it will cause the cast iron to leach into the fluid stream? Is the statement above even true? Is this statement true for all metal piping? ie., copper, stainless, sch. 40 steel? Is DI water safe for human consumption? I'm trying to understand the chemistry behind DI water.





RE: Deionized Water
Because deionized water is so pure, there is a strong driving force for minerals to be dissolved into it. This is especially true when the deionized water is slightly acidic. Stainless steel can withstand the corrosive effect of most demineralized waters. I don't think that drinking DI is a very good idea...I'm not too sure why, but I think it reaks havoc on the uptake of minerals of your cells.
Hope this helped.
RE: Deionized Water
From my experience, when plumbing DI water use 316L SS, which has been chemically protected (passivated). The chemical treatment will extend the life of the plumbing but not necessarily prevent it from corroding.
Because the water is pure (lacking ions), the natural process would be to accumulate ions, and this would be why you are observing leaching of the cast iron into water supply.
A corrosion engineer may be able to provide you with more details as to what is happening.
Hope this helps.
RE: Deionized Water
Stainless steel pipes should be fine, but you may want deaerated (no dissolved oxygen) water for cast iron or even mild steel pipes ... mechanical or chemically deaerated, like in your typical boiler feed water system.
RE: Deionized Water
As far as human consuption, DI WATER IS NOT SAFE TO DRINK! It is often call "slow death" by people in the water treatment industry. Drinking DI water on a regular basis will slowly rob the body of vital minerals, and death can occur. Now, if you drink a glass of DI water, you will not notice any adverse affects. But, it will not taste very good at all, because the water we are used to drinking actually has a small amount of flavor from the minerals it contains. In fact, if you read the labels on bottled water, you will find statments like this: "treatment by reverse osmosis, and enhanced with minerals for a pure, fresh taste."
RE: Deionized Water
I'd guess that demin water would be bad for your health if you had a diet where your water intake accounted also for most all of your daily mineral intake.
If you drank only demin water, my guess is just eat well, even eat mud, to get them minerals, and you'd be fine.
I don't think it would harm you, if your overall dietary intake was healthy, unless you drowned in it (or like, drank a cubic meter in one sitting)
Just an opinion.
Cheers//
RE: Deionized Water
RE: Deionized Water
Many communities use RO sea water for drinking, including the military.
Just my opinion.
RE: Deionized Water
Cheers//
RE: Deionized Water
PVDF is used primarily because there is virtually no leaching of trace minerals as you might get with different steels. Another reason is the water is specifically treated to remove dissolved oxygen and one of the last steps is ozination to prevent biofilm. Ozone is very corrosive in most systems, but the PVDF holds up very well.
Hope this helps.
RE: Deionized Water
Drinking and cooking with exclusively 18 megaohm demineralized water is not a healthy idea (cooking with it leaches the minerals from the food as well). I did mention that death can occur, but that is obviously an extreme case where an individual may not be getting proper nutrition in the first place. Maybe I stressed the point too much, because, in scouring the net a bit, I find that the jury still seems to be out on the dangers of drinking water of higher purities as opposed to the impurities contained in some communities' water systems.
Your point about dissolved impurities from piping material is absolutely correct, 18 megaohm demin water will dissolve any such impurities. That is why 316SS piping is used in most cases to transport water of that purity, the water will "corrode" carbon steel pipe, as strange as that might sound.
RE: Deionized Water
Rainwater has negligible mineral content too, doesn't it? But then again, rain water isn't potable water, and demin water isnt potable water. And rectangle isnt (always) a square? So one must define their specifications which lead to these terms of potable, demin, 18-MOhm (that's fairly clear), etc.
For example, is demin water pathogen free or chlorinated? Not necessarily (it is common for slime deposits to actually grow in demin tanks .. amazing little bugs). Therefore, demin waer it is not striclty potable water.
Canadian potable water quality guidelines make reference to epidemiological evidence that hardness (Ca, Mg) in water may be inversely proportional to occurence of cardiovasular disease. We all appear to be in agreement on that. Maximum levels of about 200 ppm hardness are recommended to prevent pipe and equipment scaling. Actually, adjusting demin water for a neutral or slighlty negative LSI (Langelier Stability Index), by adding calcium and alkalinity, would minimize corrosion, negating need for stainless steel (how many potable water systems are made of $tainless $teel?). In short, why would one want to use demin water for potable water system?
If demin water was to be used as potable water, would it not be required to be chlorinated? If so, adding Cl2 gas or bleach would surely take demin water out of the potable water pH range of 6.5-8.5 pH units. Then you'd at least need to add lime and/or soda ash. There's the need for minerals, again. Also, as mentioned above, taste may very well improve, too.
Bottled water is another story ... not too sure about their sanitation requirements ... likely stricter than that discussed above.
All things come together?
Cheers.
RE: Deionized Water
Surprising to meet bottled water coming from reverse osmosis plants, since bottled water comes from high quality soil springs and undergoes some sterilization (e.g. by UV, etc) to keep acceptable quality for a year. Bottled RO water (with added salts) is thought to exist only where natural potable water is very scare.
RE: Deionized Water
RE: Deionized Water
RE: Deionized Water
Why not use plastic pipes if it is so corrosive?
It is dangerous to drink to much. As earlier said the water interfear with the K - Na synaphsis. All the salt in the cell wants to even out the "salt free" environment outside the cell, thus the cells "explodes"
Petroni
RE: Deionized Water
RE: Deionized Water
This is generally done in the western world.
Besides, at the risk of being too exacting, I'd add that pure water is not totally deionized because it autoionizes by splitting into [H3O+] and [HO-]. At 25C the molar concentrations of both ions are 10^-7 (pH=7). On heating the pH drops as a result of more ionization. So, at 60C the pH drops to 6.5 and the concentrations more than double. The concentration of these ions at 60C are more than 9 times that at 0C. But, behold! Drops in pH don't mean that water becomes more acidic. Both ions appear in the same concentration keeping the water neutral.
Because of the increase in ions activities (aka concentrations) water resistivity drops with rising temperatures: the 18 megaohm.cm figure, given above by Promero, is at 25C, it drops to 4 megaohm.cm at 60C, and to about 2 megaohm.cm at 80C.
RE: Deionized Water
Wanted to know the difference between demin water and deionised waters and searched the previous posts and found your fascinating discussion. Can some one on these threads advise me whether deionised and demin waters are the same? If not, what is the difference?
Regards,
Guru
http://www.americansanskrit.com/default.html
RE: Deionized Water
RE: Deionized Water
That's why we have "acid rain".
RE: Deionized Water
The dose clearly makes the poison! If half of the 90 kg men who are killed by drinking 15 kg of water, I guess that would give water an LD50 of ~166,000 mg/kg by ingestion. Mark that one up on the MSDS sheet!
As far as the corrosivity of pure water, the more I hear about it the more confused I become (see the thread "Aluminum together with copper" in the corrosion engineering forum and you'll see what I mean. I'm starting to feel that there have been some improperly analyzed anecdotal incidents of problems with copper (and according to one poster here, even stainless steels!) in pure water services, which have led to a general condemnation of copper in pure water service- even though thousands of miles of thin-wall copper steam tracing have given years of service in contact with condensate. And what is steam condensate but hot, deoxygenated distilled water?
Note that there is a BIG difference between saying that copper will relatively rapidly corrode to failure in deionized water, and saying that copper will render deionized water unfit for purpose by contaminating it with copper ions! The latter is definitely true from what I've gathered, and is sufficient reason not to use copper in some deionized water services. Contamination concerns, rather than corrosion concerns, leads one to select PVDF rather than any metal in semiconductor water services. However, contamination by copper ions is insufficient reason to reject copper for use in ALL deionized water services- it depends on WHY the water was deionized in the first place and what its intended use is.