Why does a stable and efficient water cycle necessary for a inhabitable planet?
831230
inhabitable means fit for habitation contrary to other beliefs, uninhabitable means not fit for habitation\n\nthe water cycle needs to be relatively stable and efficient for life to 'get a hold' on land. if organisms were to evolve to live on land and then had no water for a hundred thousand years, then they would all die. also, variations in water turbidity, salinity and temperature are all affected in some way by the water cycle affecting life, marine and terrestrial.
1122743
That's when one collects rain water in  large containers or pond for latter use in irrigation, toilet flushing, showering, car washing, etc.  It saves natural resources.  In fact it doesn't take much investment of effort...depending, however, on the complexities of the system.
395247
This is really impossible to say, being both a science and political question.\n\nReactors need to be close enough to the energy grid and populations that the energy lost in transmission is minimal.  On the other hand, far from populations to limit the ramifications of a meltdown.\n\nTransporting waste is risky itself.  So easy safe access to storage sites is important.  On the other hand, risk of contaminated water and people stumbling on it would have it far away.  Not to mention the possible ecological side-effects to local fauna.\n\nThere's no best answer in a real world, just some less awful ones.
419070
Water..We always have the exact same amount on earth. It just keeps changing forms.
853505
life needs not only oxygen but othere conditions as well. Life needs essentailly he fore of gravity for the proceses of life to be active .It is graiy tha keeps the sir balanket over the surfaxce oif he earth . But for that , the air would vanish into thin air ! - would anish into space . Water would not flow and our food would not go doen  our throat and would not even be able to defecate . aain the climate is also imporant . We hae go to be at a distncefrom the dun hat would be expose us to a ligh and heat that is cinsucive to the development of live and tolerable to life .ALL  he planets around the sun are not locaed at a sistance very conducive to the deelopmemt of life like us .and all of hem dfo not hav a gaviy  tha is suitable for the fuctioning of our system . We are not independent of our great mother earth. We will not survive in any planet which dose not hae an amospher  and gavity like the earth. Oxygen alone won't  help us live .Since the building blocks of all elemens ar the same - electron and proton - we would be able create oxyen in any planet by a suiable process that man would be able to create by manipulaing the numbver of electrons in the aoms of any subasance aailable in any pkanet . We do not hae to transfer oxygen anywhere . we can create oxygen from   whatever is available anywhere.
685026
u also need to create a biosphere,,self contained sealed enviroment that has oxygen producing plants and also plants for food,and a filtering system for water. and a waste mangement system all self contained. and a communications system back to earth.
47495
I would say the Sun. You need it in order to create evaporation to create the clouds that produce rain. Without it, there would be no rain.\n\nAfter reading the additional comments, the sun is still more important than rain. Sure, we can create our own light but it isn't economically feasible to create enough sources of light for plants to photosynthesize and create Oxygen for us to breathe. The Sun's light covers a much wider area than we could imagine or build for, at least economically speaking.\n\nWe can live without water for a short time, but we can't live without oxygen. If the plants stop producing oxygen because of lack of light, we'll die even if we have an abundance of water.
620149
"Rain plays a major role in the hydrologic cycle in which moisture from the oceans evaporates, condenses into clouds, precipitates back to earth, and eventually returns to the ocean via streams and rivers to repeat the cycle again. There is also a small amount of water vapor that respires from plants and evaporates to join other water molecules in condensing into clouds"\n\n" 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration."\n\n The total amount, or mass, of water in the water cycle remains essentially constant, as does the amount of water in each reservoir of the water cycle. This means that rate of water added to one reservoir must equal, on average over time, the rate of water leaving the same reservoir.\n\nThe adjacent table (at the site below) contains the amount of water that falls as precipitation or rises as evaporation, for both the land and oceans. The runoff and groundwater discharge from the land to the oceans is also included. From the law of the conservation of mass, whatever water moves into a reservoir, on average, the same volume must leave. For example, 107 thousand cubic km (107 × 10³ km³) of water falls on land each year as precipitation. This is equal to the sum of the evaporation (71 × 10³ km³/year) and runoff (36 × 10³ km³/year) of water from the land."
515445
because water is a renewable resource. There is as much water on the earth today as there was when the earth formed.  The argument that not all of that water is as drinkable today as it was then is a weak one. The water from a treatment plant (post treatment) is usually cleaner than plain tapwater!
759317
The normal cycle is (very simplified): rain, transportation to sea, evaporation.\n\nThe main thing that mankind does to change this is after the rain has fallen and before it reaches the sea.  The main thing being irrigation which diverts water from the river into the surrounding land.  Obviously when water is soaked into the ground it cannot evaporate and so the 'residence time' in this part of the cycle is increased.\nBuilding damns and other structures (ie. cities) will also have similar effects by diverting the natural course of a river.\nWith global warming comes another problem.  Obviously the warmer something is the more energy it has.  This extra energy causes an unstable atmosphere leading to increased rainfall in some areas and less in others.  Rising sea temperature, which is also connected to global warming, will increase the rate of evaporation (which is why there are more hurricanes in the Atlantic).
1128499
Why couldn't someone come up with an engine were you needed only water...I mean the earth is made up of like 70% water.
643686
It would make water (H2O).
82704
who needs the water cycle with out the sun. all living things would die without the sun.
672515
Its not really important.\n\nThey're saying that someday the earth could heat up enough to melt the north and south poles and burry us all in water.  The sea is currently rising at a rate of like a half inch each year.  However, climet changes all of the time and so the greenhouse effect isn't necessarily a concern.
1159452
mainly to do with temperature and climate in various parts of the world be unable to sustain a  natural water supply
187860
Water is used in about all of the chemical processes in the body. Therefore it is a waste product in most of these reactions. The very act of breathing requires the use of water. No machine is so efficient as to have absolutely no loss in any of the variables involved in it's working. Some creatures are very efficient at retaining water but at a price to other bodily functions and even then they will eventually dehydrate and die without water.\nThis is really a pretty simple concept.
148940
I think it would only be possible if there was also lots of water on the planet as well as good solar radiation being close to a star and carbon dioxide. Also it would be helpful if there was nitrogen in the soil since plants absorb nutrients from the soil. There would also need to be rainfall on the planet, but if there wasn't irrigation and watering by caretakers could be sufficient.\n\nAnd what about terraforming? Mars has an atmosphere and I beieve carbon dioxide. Could plants grow on Mars? We'd have to transport millions of gallons of water in our ships and keep the water from sinking deep into the planet. Why would we want to do that? It could cost a trillion dollars. The moon has no atmosphere I'm not sure it could be terraformed. Just a thought.