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Comment by brrt | Hacker News Reader

The current state of the art (reverse osmosis) is already fairly good. The first link I found [1] demonstrates the increase in efficiency - we're talking about roughly 3 kWh/m3. I don't recall exactly, but I think that is in an order of 5 of the theoretic maximum.

At an average, rather immodest level of water consumption per capita (~1580 m3/annum), then this is about ~4740kWh per year, or 13 kWh per day. I'd say this is significant, but then:

For comparison, current energy use per capita in the USA is 7000kg-oil-equivalent [2] (or 81000 kWh [3]), so an additional 4740 kWh is about 5%.

The real problem is that people use absolutely indecent amounts of energy and water and other resources, usually for no good reason at all...

[1] https://s3.amazonaws.com/academia.edu.documents/45145253/The... [2] https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locat... [3] https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent

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Thanks for the stats -- I actually just installed a solar array on my house which should produce around 8000kWh/yr which is in the ballpark of how much energy our 2-person household would need to desalinate our own water, so it's nice to have a tangible metric (and to know it could be done on our own roof space)... ~$24k installed, does not include cost of desalination plant :D

Wonder what level of energy is needed for water transportation and pumping inside cities. Btw for reference the water consumption per capita is much lower and very skewed in developing countries. It is all about access and fights over that. I hope for many coastal regions desalination might become the economically viable option

Are those numbers right? 1580 m3/year is 4.3 m3 or 1100 gallons per day. http://www.theworldcounts.com/stories/average-daily-water-us... says 100 to 175 gallons per day per person.

I got that number from here - tried to find a more 'official' source, but water isn't as well documented as energy.

Note that those numbers when I last looked into it typically include industrial and agricultural water use - residential water consumption is usually approximately 15% of total water use, so that fits reasonably.

One problem is that in many countries, water consumers (e.g. farmers) are able to withdraw water from their own soil, and so nobody really knows how much water that is, although it's possible to make educated guesses.

[1] https://www.statista.com/statistics/263156/water-consumption...

Are they taking into consideration the water it takes to produce the food that you eat in that 1100 gpd figure? Also, the amount of water that you use to shower/wash dishes/flush/water your lawn?

Seems plausible within an order of magnitude. 1 pound of beef takes ~1,800 gallons of water.

Please do not spread this twisted truth.

1. Those numbers are from all the rain hitting the pasture divided by by the cows mass (that is eatable)

1.a including whatever it eats

2. The way it's told makes it seem that none of the water is reused which is not true Though beef is a water intensive 'crop' it is not as bad as certain people makes it out to be.

Edit: formatting

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