Deionized Water 2

[promero]

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.

 

[WasteMinEngineer]

Quality of rain water you receive depends greatly on where you live. If you live in an area that has very active municipal solid waste incinerators that burns thermometers and plastics and a few power plants burning coal, I don't think the quality of the rain water in that area would be as good as say rain water collected in a middle of a large desert.

That's why we have "acid rain".

 

[moltenmetal]

Water, demin or otherwise, can and DOES kill people. It kills by upsetting the body's electrolyte balance, which is not really the same as saying that it "leaches minerals from the body". Numerous deaths have been reported amongst youths who have taken the illicit drug "ecstacy", which can cause an enhanced thirst as a side effect when taken to excess. In one case, a 21 yr old man in England perished from brain swelling which occured after he totally upset his body's electrolyte/osmotic balance by drinking 15 litres of water in less than an hour. Athletes can also experience serious problems due to drinking water with insufficient electrolyte content to replenish water and electrolytes lost through perspiration. So, clearly it is not a good idea to drink water which has been totally demineralized- whether that is by means of RO, distillation or IX.

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.