Effect of drinking ultra-pure water

Question

What would be the effect if someone were to drink ultra-pure water with an electrical resistivity of $18 \, \mathrm{M} \Omega \! \cdot \! \text{cm}$?

Would they immediately die? Would they just need to pee more? Would $\ce{CO2}$ from the air (after the bottle is opened) and whatever's in saliva dissolve into the water making it much less pure before it gets into the important parts of their digestive tract?

What would be the threshold for bad things to happen — a teaspoon, a liter, 12 gallons in 10 minutes (at which point I assume regular water would kill you)?

I'm not sure what the science here would be.

Answer 1

What would be the effect if someone were to drink ultra-pure, 18 M-ohm water?

Not much, although if they drank many gallons of the water it could be a problem.

Would they immediately die?

No.

Would they just need to pee more?

Probably.

Would $\ce{CO2}$ from the air (after the bottle is opened) and whatever's in saliva dissolve into the water making it much less pure before it gets into the important parts of their digestive tract?

It would become orders of magnitude less pure as soon as it mixed with their saliva and then their gastric juices. Same as regular water.

What would be the threshold for bad things to happen -- a teaspoon, a liter, 12 gallons in 10 minutes (at which point I assume regular water would kill you)?

I don't think the effect would be that different from drinking regular water. All over the internet there is this idea that super pure water is somehow too pure or dangerous, no good evidence or mechanism is ever presented.

Water is toxic primarily because it dilutes the sodium and potassium ions in your body, leading to Hyponatremia or possibly the far more dangerous Hypokalemia. The normal level of $\ce{Na+}$ in blood plasma is about 135 millimolar (mM), and the normal level of $\ce{K+}$ is about 5 mM.

A very rough approximation to understanding how toxic water can be would then be to compare the concentration difference of sodium (or potassium) between the ingested water and the blood. A 25 micromolar -- i.e. 25 μM or 0.000025 molar solution of sodium hydroxide has a conductivity of about 6.7 microsiemens per cm, more than 100-fold higher than "pure" 18.2 megohm water (0.055 microsiemens per cm). According to this rough difference-based model, the ability of the very dilute sodium ion solution to cause problems is proportional to (135 - 0.025) mM, and the ability of the "pure" water to cause problems is (135 - 0) mM. For nearly biological or medical conditions of interest, 135 mM is not really different from 134.975 mM, and so ultra-pure water is not really more dangerous than everyday drinking water.

Answer 2

Pure water (i.e. 18 Megohm conductivity) is still just water. If you don't drink so much as to cause water intoxication, it would be no different physiologically from drinking tap water or bottled water.

Answer 3

1. At elementary level, we do learn that salts are important for our body, actually very much for normal day-to-day functioning of human body (as asserted by Curt F.)
2. So from point of view of elementary level, pure water does causes harm.
3. But as new research and innovative science suggests, which we do understand from the answer of Curt F.; there might be actually, or in fact (because my textbook also says that Osmotic pressure-Colligative property is one the most important and has fundamental role in earth's biological system.) it is partially wrong to say that salts are important for our body, so we should drink only that water which either contains little or enough salt content in it.
4. Finally I would be quoting from Curt F. to further extend my point of view:

"I don't think the effect would be that different from drinking regular water. All over the internet there is this idea that super pure water is somehow too pure or dangerous, no good evidence or mechanism is ever presented. Water is toxic primarily because it dilutes the sodium and potassium ions in your body, leading to Hyponatremia or possibly the far more dangerous Hypokalemia. The normal level of Na+ in blood plasma is about 135 millimolar (mM), and the normal level of K+ is about 5 mM"...

... "According to this rough difference-based model, the ability of the very dilute sodium ion solution to cause problems is proportional to (135 - 0.025) mM, and the ability of the "pure" water to cause problems is (135 - 0) mM. For nearly biological or medical conditions of interest, 135 mM is not really different from 134.975 mM, and so ultra-pure water is not really more dangerous than everyday drinking water."

5. This means at more advance level, especially research-one; it is easy to conclude that a slight difference wouldn't mind your body. You have saliva in your mouth-the liquid lining on your oesophagus-and digestive juices in your stomach and intestines, which (in my view) has the capacity to reform the content of (practically) any kind of pure water.

6. Intially I was thinking to write it as a comment in response to Curt F.'s answer but i don't have 50 reputation points. Mind me, for any mistake and therefore correct my even the slightest of slightest mistakes.

Answer 4

Would they immediately die?

No.

I agree, no. But if long time drink pure water, such as 18 M-ohm water, it could cause shortage of u-elements, such as Zn, Se, Fe,..., even all those very,very small quantity, but important for the life, the health... Normally speaking, drink normal water is the best.

the question is how to get the pure water, 18 M-ohm? Could be expensive. It can be said using two methods: Physical or Chemical. Steam method is physical. Ion change is chemical method. Both methods changed property of natural/original water. not good. especially, chemical method. More or less, chemical reaction take place, the products changed. pH changed. some thing changed,... natural/original is the best, need the water, parents, grand parents, grand and grand parents' drinking.