Hacker News Reader

Comment by dpcan | Hacker News Reader

This is an article about why we can't drink salt water :)

On hn I usually expect these titles to be tongue in cheek and the article to be about an invention that would allow us to inexpensively purify sea water for drinking.

Speaking of which, IS there such a device? If not, why not?

View on HN

http://www.thewatercone.com/Index.html

That is so cool. We built solar stills in scouts but this one seems really practical.

And you can build such a thing on the sea beach with a plastic bag (which are a plenty on the beaches everywhere in the world, imho).

Based on a solar still, http://en.wikipedia.org/wiki/Solar_still, there is the Water Pyramid for villages, http://en.wikipedia.org/wiki/Water_Pyramid and the Water Cone for personal use: http://www.thewatercone.com/Index.html

There's a Canadian startup making a device that gets (part of) its energy from the difference of ion concentrations in salt/desalinated water. http://saltworkstech.com/

Desalination plants? Sure, they're widely used in many dry parts of the world, particularly the Middle East, but also increasingly in Australia.

http://en.wikipedia.org/wiki/Desalination

According to International Desalination Association 2009, there are 14,451 desalination plants in operation worldwide, producing 59.9 million cubic meters per day (15.8 billion gallons a day), a year on year increase of 12.3%

Define inexpensive.

A lady has just put up a group trip to row across the Caribbean Sea. 14 people will row a double-hull boat over more than a month. They'll definitely need to desalinate sea water.

http://globetrooper.com/caribbean-sea-row-2012-barbados-jama...

Katadyn does desalinators for civilians.

http://www.katadyn.com/usen/katadyn-products/products/katady...

For those interested in watermakers, it's possible (and perhaps affordable) to build your own!

http://www.albin25.eu/our-a25ak-dido/34-dido-stories/60-dido...

In the film Waterworld, they have a device to purify urine - you crank the handle - but funnily enough they aren't using the device to clean seawater. Just another plot hole...

They have desalination plants in the middle east. The problem with those is that they are very energy intensive.

The pacific is worth mentioning too...Singapore in particular, and Australia increasingly so. A handful of southern US states are getting things ramped up too.

I think solar heat desalination plants in very hot climates like that could be more practical. +40C is fairly common in Singapore and the Middle East

Another problem is the output flow is more saline, which affects sea life.

Can't the salt be safely dumped on land?

It's not salt but brine - water with a high concentration of salt. If put on land it would kill all plant life excepting a few highly salt tolerant species.

There's a large desal plant in Florida too, it supplies part of the water that I drink. You're right in that it's energy intensive, but at least in our part of the world the largest problem was water quality. There's a lot of biomass floating around in sea water and it means having to constantly repair the filters. I believe there was a big issue with an invasive species of mussels as well that do quite a bit of damage.

http://www.tampabaywater.org/facilities/desalination_plant/i...

The suits in the novel "Dune" do that as well. But there is no ocean or other open bodies of water on the planet in the story.

Evaporation would leave the salt (and most other minerals) behind.

I suppose there exist devices for re-capturing the condensed (=drinking) water out of sea water. I don't know why they're not common; my guess is they're just not economical/too hard on maintenance.

The point is that you condense the evaporated water. You can do this more than once to get purer water. One thing though, you'll end up with a significantly smaller amount of water than you started with, so you have to compensate for that.

> Evaporation would leave the salt (and most other minerals)

That's a good point. I can't say I know the answer, but I've read/heard that drinking this mineral-free water can have long-term adverse health effects (leaches minerals from your body into the mineral free water?). I see articles for/against this theory. Interested to hear comments from anybody who actually knows details.

Of course dying from thirst or salt poisoning in a few days versus the long-term prospect of slow mineral loss make the choice a no-brainer in the case of an emergency.

"I've read/heard that drinking this mineral-free water can have long-term adverse health effects (leaches minerals from your body into the mineral free water?). I see articles for/against this theory. Interested to hear comments from anybody who actually knows details."

Take a look at:

http://www.finishing.com/156/65.shtml

My favorite quote from that thread:

"If it is a concern & all you have to drink is ultrapure water, you can stir the water with a metal stainless spoon or your finger first & it will magically transform itself from ultrapure water to just water."

Thanks for the link, but not very convincing. The site itself is a forum for the metal finishing industry; like chrome and silver plating, not something I'd hold up as expert in human health and diet.

Most of the discussion oscillates between "Yes it's harmful. If you want to consume DI water that does x, do so at your peril." and "No it's not harmful. Why are you afraid of something we already use for x?"

Not really, and for the same reasons the combustion engine is still king: so far, there's almost always more economical alternatives. The biggest issue is the cost of energy.

Such things do exist, but they are so energy-intensive (water has to evaporate) that they're only used in extreme emergencies. Plus, doing it on a large scale would have effects on things we don't fully understand yet (sea levels etc).

> (sea levels etc).

Well, no, because the water that comes out of the sea, one way or the other, will probably go back there.

The main problem with desalination is what to do with all the salt it produces. I mean, you can dump it at sea, but then you're poisoning some patch of sea and hoping the salt will disperse.

You could purify and sell the salt as table salt, etc.

Given that there is a commercial market for sea salt, dumping it back in the sea would seem counter productive...

Desal plants produce prodigious amounts of salt. Some of it can be sold, but not all of it. You still wind up with piles of the stuff that need to go somewhere.

Unless you are doing this on a scale that (almost) literally boils the oceans, I doubt that really is a problem. The oceans are _big_, and not that salty.

Also, as another comment already said, you might be able to sell the salt instead.

> (water has to evaporate)

The most common method of desalination is reverse osmosis. Still energy intensive, but presumably less so than evaporation.

http://en.wikipedia.org/wiki/Reverse_osmosis#Desalination

Evaporation also becomes a lot cheaper when you get most of the energy from the waste heat of a power plant.

I've got an engineering question posted on my site regarding a portable desalination device (potentially using reverse osmosis), if anyone has ideas: http://zombal.com/zomb/scientific-design/emergency-desalinat...

Like one of these? http://www.campingsurvival.com/kahaemdewama.html

Reply on news.ycombinator.com