[katieHaylor (OP)]

Caroline asks:

Is there a finite amount of fresh water on earth?

What do you think?

[alancalverd]

There is a finite amount of water on the planet. There is a continuous cycle of evaporation from the ocean surfaces  and precipitation of fresh water as rain or snow so the balance between salt and fresh water varies on a geological timescale. During cold periods and ice ages, there is more water in the soil and ice caps and less in the seas and clouds.

[jeffreyH]

The alternative to finite is infinite. So it has to be finite by definition.

[chiralSPO]

The mass of all the water on Earth must be less than the mass of the Earth. Therefore, because the Earth has a finite mass, there must be a finite mass of water on Earth.

Another interpretation of the question, will there be water available on Earth for infinite amount of time, also gets a firm "no" answer, but might be a little closer to "yes." The water on Earth is almost entirely recycled from one form and place to another. This has gone on for billions of years, and will likely continue for billions more, but probably not trillions, and certainly not infinitely long.

[alancalverd]

As the cycle involves gaseous water in the atmosphere, and water has the lowest  molecular weight of the active constituents of the atmosphere, it will all eventually float off into space.

[evan_au]

Another aspect of the question is whether we have enough unpolluted water in the right places to meet the needs of humanity and the ecosystem.
- A number of countries have border arguments about who has the right to the water in rivers that cross their borders. Sooner or later, this will escalate into wars.
- We dam rivers to provide a source of fresh water. But the dams start to silt up in 20 years or so, and reinforced concrete starts to fall apart after 100 years. So these have a limited lifetime.
- Most countries spray water onto open fields, and most of it evaporates without helping anyone.
- Agricultural runoff is polluting waterways
- Some countries like Israel have made great progress in drip irrigation - delivering the right amount of water to the right plant at the right time.

We don't like to think about it, but humans tend to defecate in our drinking water.

We have made the connection less direct in some parts of the world, with sewage processing plants.

But a move to supplement the drinking water of an inland Australian town with water purified from the sewage treatment plant (by reverse osmosis) was met with mass protests.

Meanwhile, a number of coastal cities in Australia have built large-scale reverse-osmosis plants drawing on seawater, which has a far higher osmotic pressure than the outflow of a sewage treatment plant (ie it is far more energy-intensive to extract fresh water from seawater). Ironically, the intake for the Sydney desalination plant was not so far from the ocean release point for the sewage treatment plant.

[alancalverd]

But a move to supplement the drinking water of an inland Australian town with water purified from the sewage treatment plant (by reverse osmosis) was met with mass protests.

Interesting. Thames water is estimated to have been drunk 13 times between falling from the sky around Oxford and reaching your tap in east London. Us Cockneys and Essex Boys was brung up on it.

[yor_on]

Yes, but we might get a refill now and then.

" No, H2O cannot exist in stars, but H and O separately can. Hydrogen is the basic building material of the universe, created in the Big Bang. Oxygen is created by nuclear reactions in stars. If you put H and O together in the cold of space, you get H2O. There are enormous amounts of water in space. In fact, nearly all of the oxygen in space is in the form of water or carbon monoxide. Similarly, most the carbon and nitrogen in space are also in their most hydrogenated forms: methane and ammonia. "

And ...  .livescience.com/33391-where-did-water-come-from.html