# Conservation of water molecules. Where and when do water molecules break down? **URL:** \ **Category:** Factual Questions\ **Created:** [September 20, 2003, 6:11am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774 "2003-09-20T06:11:07Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [September 20, 2003, 6:11am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/1 "2003-09-20T06:11:07Z")
I was just thinking. Does water get created anymore? Or is the amount of water on the planet pretty much going to stay the same for the time being? I mean on a molecular basis that is-- wether it be ice, water or in vapor form. How hard is it to create water? ---
**Author:** ![Run4YourLife](https://avatars.discourse-cdn.com/v4/letter/r/a9a28c/32.png) [@Run4YourLife](https://boards.straightdope.com/u/Run4YourLife)\ **Post date:** [September 20, 2003, 6:23am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/2 "2003-09-20T06:23:05Z")
Oh man, any chemistry student has made water before. Basically all you need to do is get Oxygen and Hydrogen and get them to react with heat and you have water. The problem is that this is impossible to do on a large scale. ---
**Author:** ![Run4YourLife](https://avatars.discourse-cdn.com/v4/letter/r/a9a28c/32.png) [@Run4YourLife](https://boards.straightdope.com/u/Run4YourLife)\ **Post date:** [September 20, 2003, 6:25am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/3 "2003-09-20T06:25:34Z")
Much more complex exlpanation: ``` KE0103 Mikko Pennanen 02C Water ``` - the liquid of life Water is one of the most basic necessities of life. It covers 80% of the earth¡¦s surface, makes up 75% of a person¡¦s mass and up to 90% of the mass of plants. Plants need it for photosynthesis. People need it obviously to drink and also to bathe. The whole industrialized world is dependant on water. But what makes water special and vital? Hold on, you¡¦re about to find out. A water molecule (H2O) consists of one oxygen (O) and two hydrogen (H) atoms. A water molecule is formed when hydrogen gets in contact with oxygen. Since oxygen atoms have six and hydrogen atoms have one electron on their outermost shell the easiest way for both to get an octet is to form a molecule with one oxygen and two hydrogen atoms. This happens the following way: oxygen, which has two single electrons on its outermost shell of electrons, and two hydrogen atoms, which both have one electron, join one another by giving one electron to a shared pair of electrons forming two covalent bonds. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [September 20, 2003, 6:31am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/4 "2003-09-20T06:31:54Z")
That is an awsome post. However, I meant to narrow my Question to nature. What happens in nature that changes the amount of water on the planet? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 20, 2003, 6:38am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/5 "2003-09-20T06:38:27Z")
Well, the water on Venus was mostly lost by Photodissociation; from [here-](http://gould.as.arizona.edu/~mmeyer/ast202/lect16.html) Loss of Water in Venus’s Atmosphere: \*\*1. An H2O molecule (present in atmosphere as water vapor) is broken down by UV sunlight. 2. The hydrogen atoms (light) are moving fast (because they are hot). If the velocity is high enough they escape to space. 3. The oxygen atom oxidizes surface minerals. \*\* The oxygen remains on Venus mostly in the form of CO2; the hyrogen is mostly gone for ever. This is hardly happening at all on Earth, so we are not losing our water very quickly; we have a cool, thin upper atmosphere whereas Venus’s is thick and bathed in much stronger sunlight. But in a billion or two years or so the Earth would lose all its water, as the Sun Heats up; eventually the Sun will become a red giant, but I expect the Earth will have been uninhabitable for a long time by then. * * * SF worldbuilding at [http://www.orionsarm.com/main.html](http://www.orionsarm.com/main.html) ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [September 20, 2003, 6:45am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/6 "2003-09-20T06:45:08Z")
[The hydrologic cycle](http://www.ec.gc.ca/water/en/nature/prop/e_cycle.htm) > [@](#): > > The sun-powered cycle > The endless circulation of water from the atmosphere to the earth and its return to the atmosphere through condensation, precipitation, evaporation and transpiration is called the hydrologic cycle. > > Heating of the ocean water by the sun is the key process that keeps the hydrologic cycle in motion. Water evaporates, then falls as precipitation in the form of rain, hail, snow, sleet, drizzle or fog. On its way to earth some precipitation may evaporate or, when it falls over land, be intercepted by vegetation before reaching the ground. The cycle continues in three different ways: [Is water created or destroyed during the Hydrologic Cycle?](http://www.water-distillers.biz/faq/is-water-created-or-destroyed-during-the-hydrologic-cycle.htm) > [@](#): > > During the Hydrologic Cycle, the earth’s water is cleansed – it is not created or destroyed. Simply put, the water is continually changing location and form. The water you drink today may have been lapped up by dinosaurs millions of years ago, or used to fill Julius Caesar’s bathing pool. The water we use now is the same supply the human race started with. Its quality is renewed again and again by the natural Hydrologic Cycle ---
**Author:** ![Roches](https://avatars.discourse-cdn.com/v4/letter/r/bc8723/32.png) [@Roches](https://boards.straightdope.com/u/Roches)\ **Post date:** [September 20, 2003, 7:47am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/7 "2003-09-20T07:47:55Z")
Run4YourLife: I guess you mean H2 + 1/2 O2 --\> H2O; the experiment would be useful for verifying the calculated enthalpy of formation of water, but I don’t think it’s practical. I can only remember making water the boring way, NaOH + HCl --\> H2O + NaCl… =) The reaction you described is probably much better to conduct electrochemically. These are the half-reactions in a fuel cell: Anode: 2 H2 --\> 4 H+ + 4 e- Cathode: O2 + 4 H+ --\> 2 H2O Overall: 2 H2 + O2 --\> 2 H2O Most of the water on Earth probably formed by this reaction, driven most likely by electrical activity rather than just heat. Some paleogeologists believe that the comets bombarding the Earth early in its existence may have provided much of the water also. I can think of a few other ways that water can be added to or removed from the hydrologic cycle: - By organisms. Organisms using O2 as the final electron acceptor in cellular respiration (everything except some bacteria) end up producing some water in that reaction. Many organisms use water as a source of hydrogen and oxygen in synthesizing organic molecules; plants require especially large amounts of water for making glucose from CO2 in photosynthesis. - Volcanic activity, which forms sulfuric acid by a process that consumes water. - By ultraviolet light. Ozone can be broken apart by ultraviolet light to form a species that reacts with water to give a molecule called the “hydroxyl radical”, which acts as a detergent in the atmosphere. Most hydroxyl radicals end up in reactions that yield water, so this doesn’t change much. - By precipitation. The major reason why Earth doesn’t have much CO2 in its atmosphere is that, when it’s dissolved in water, it reacts easily with calcium to form calcium carbonate – limestone. At certain pH, water can react with different ions to give insoluble precipitates (e.g Al(OH3), but I’m not sure how significant this is. - Combustion. When organic compounds burn, they release water vapor. (generally: x CaHbOc --\> m CO2 + n H2O) Since humans like to burn things, we end up releasing a lot of water vapor into the atmosphere – far more than would have been released by fires before humans evolved. Water vapor is a greenhouse gas, and greenhouse gases lead to global warming, and global warming leads to more water vapor in the atmosphere, and so on… I’m not sure how significant each of these are. I would think that the most important source of water outside the hydrologic cycle is combustion of organic matter. The most important sink (the opposite of a source) would likely be the incorporation of water into organic molecules, mostly by plants and other photosynthetic organisms. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 20, 2003, 10:07am UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/8 "2003-09-20T10:07:34Z")
Since we are not being bombarded by comets at this moment in our history, and we are not losing much water to space by photodissociation, the amount of water on Earth remains more or less the same over time. The Hydrological cycle only removes water temporarily- even the waterthat is lost by subduction into the Eart’hs crust will resurface via volcanoes- actually, there is no guarantee that geological cycles are always evenly balanced- for more than a billion years, more carbon has entered the crust than left it, so we are gradually running out of CO2. More important for the survival of the Human species is the balance of salt waterto fresh- much of the world is deficient in fresh water, and places were it is abundant, like Antarctica and Canada, are cold and the water is often present as ice. To obtain fresh water for agriculture in many parts of the world expensive energy is required. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [September 20, 2003, 2:17pm UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/9 "2003-09-20T14:17:49Z")
Thankyou, those are the types of answers I was looking for, especially this one; "_During the Hydrologic Cycle, the earth’s water is cleansed – it is not created or destroyed. Simply put, the water is continually changing location and form. The water you drink today may have been lapped up by dinosaurs millions of years ago, or used to fill Julius Caesar’s bathing pool. The water we use now is the same supply the human race started with. Its quality is renewed again and again by the natural Hydrologic Cycle "_ And **Roches** post too. **eburacum** brings up a good point too, are the prosesses evenly producing and removing water molecules from the Earth or not. And how much is broken down or produced by organisms, and natural chemical reaction. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [September 20, 2003, 2:19pm UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/10 "2003-09-20T14:19:11Z")
Forgot to add; Are there any natural prosesses that consistently remove or add water to the supply? ---
**Author:** ![viking](https://avatars.discourse-cdn.com/v4/letter/v/bc79bd/32.png) [@viking](https://boards.straightdope.com/u/viking)\ **Post date:** [September 20, 2003, 5:20pm UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/11 "2003-09-20T17:20:04Z")
Wow. That cite on the hydrologic cycle is just plain wrong. The respiration-photosynthesis is 6CO2 + 12H2O \<—\> C6H12O6 + 6O2 + 6H2O So basically, with every breath you take, you destroy and create new water molecules. They are not simply passed through as the same molecule, as if they were they wouldn’t show up. I honestly can’t remember the full Creb’s cycle anymore (heck, I can’t even remember if it’s spelled with a C or a K 🙂 ), but yes, individual water molecules are constantly being made and broken in plants and animals. Not in evaporation and rain, though, those will be the same molecules being moved around. As for natural processes that consistently change the supply, probably not today, so much. Basically, when plants first evolved, there was no oxygen around, so the early plants (or aerobic microbes to be picky) used up a net of 2 water molecules for each oxygen in the atmosphere today. That process kinda stabilised, though, when the biomass (carbon) and atmospheric oxygen pools did. Then there was a period of a few million years where a bunch of biomass got sequestered into the ground as fossil fuels. That would also have used up water, on average. Now, we’re taking some of that biomass out of the ground, and putting it back into the atmosphere and biosphere. This will also release some of the water stored those millions of years ago. But you may not consider this a natural process. Of course, it’s possible that biomass is still being accumulated and sequestered in peat bogs somewhere; this would also remove water from circulation. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [September 20, 2003, 10:54pm UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/12 "2003-09-20T22:54:52Z")
Concerning hydrogen burning with oxygen: OF COURSE ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [September 20, 2003, 10:56pm UTC](https://boards.straightdope.com/t/conservation-of-water-molecules-where-and-when-do-water-molecules-break-down/202774/13 "2003-09-20T22:56:06Z")
Concerning hydrogen burning with oxygen: OF COURSE it forms water. Water is incredibly stable. Hardly anything reacts with it. This is why pure water doesn’t go bad (mostly). If it’s not going to form water, what do you propose that it does form?