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Comment by helge9210 | Hacker News Reader

> It is incredibly hard to create a fresh water from salty one.

Fresh water is created from the salty water by evaporation all the time.

Indeed, and it's interesting to note that this natural desalination process also incorporates long-term storage mechanisms. Historically, vast quantities of freshwater have been stored in the form of snow packs and glaciers. However, in our changing climate, this storage is not occurring at the same scale as it used to. This could potentially exacerbate future water scarcity issues, making man-made desalination techniques even more crucial. As challenging as creating freshwater from saltwater may be, it's a puzzle we need to solve with urgency.

on the other hand, global warming will pump much more water in the atmosphere, and we will have more precipitation. In fact, global warming would not be a problem at all if what I said above was not true. CO2 alone could only raise the temperature by 1C no matter how much we would put in the air (by year 2100). The water vapor creates a positive feedback loop that warms it far beyond what CO2 can do alone.

But that's not actually helpful. Occasional massive rains don't refill aquifers very well. There needs to be a buffer to allow water to slowly make it's way into the system in a manageable way. Currently that is mountain snow melting over the warm season.

I mean, sure, but never in enough volumes to be actually usable by us. It’s not like we can capture every single evaporated water droplet before it cools to form fresh water.

So while technically it happens all the time, practically it’s as if it isn’t happening at all when it comes to the concerns talked about here, specifically the quantity of available fresh water declining.

I think you are quite wrong about that. The evaporated ocean water becomes rain. Evaporated ocean water is the source of over 80% of all rain on earth.

And most of that rain is going to go into the ocean again. Or be distributed in a large area. Neither of which can really be captured in any sort of predictable and scalable manner.

You know, unless we build a massive “roof” of devices to capture all that rain. Literally covering the entire planet. At that point yeah it would dev a reasonable thing to bring up in the context of fresh water reserves falling.

So I very much stand by the point that while, sure, it happens all the time, that does nothing to actually help with the topic at hand.

The rain can be captured by farms.

> in any sort of predictable and scalable manner.

How?

Rain is not predictable at the scale of a crop season. Rain is not scalable, it’s extremely localized.

Rain happens, and when it does your crops get watered, but you can’t in any way shape or form rely on that.

About 80% of that rain happens back over the ocean, and then about 25% of the rain that happens over land actually gets captured as ground water. Even that isn’t the main point though, the issue is we’re currently using water faster than rain replenishes it in many places. At worst as I understand it, in some places they’ve collapsed their aquifers by over-pulling from them, and that means less of the rainfall in those areas will be recoverable in the future. At some point we have to enter a mode where we only pull water in a way that is sustainable or we’ll suddenly find that we do indeed need desalinization to keep up with our use.

This is where essentially all freshwater comes from.

That’s great and all but how does that help with the issue of that freshwater being depleted? Which is the topic at hand.

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