8 ms·

6 litres / metre-squared per hour. We require 130 litres / person per day in Europe. A town of 10,000 people would require 1,300,000 litres / day = ~54,000 lit

6 litres / metre-squared per hour. We require 130 litres / person per day in Europe. A town of 10,000 people would require 1,300,000 litres / day = ~54,000 litres / hour = 9000 metres-squared. A facility of 100 x 100 x 1 m seems feasible. Based on those calculations, this all seems quite practical. I do wonder how frequently the filters need to be changed, though.

Kayou 9y ago
I thought 130 litres/person was quiet high and probably included things like water to grow vegetables, but no, one shower is between 30 et 50 litres and each time you go to the bathroom, it's 10 litres of drinkable water. Of course, I you have saltwater and no freshwater, you would probably use saltwater in your toilets, so that could reduce the daily usage of at least 20 litres. But then, if you consider agriculture and manufacturing, I guess that the number of 130litres/person would blow up completely.
- positivecomment 9y ago
  Maybe people can also shower with saltwater followed by a quick rinse in drinkable water. That would reduce the usage drastically. I couldn't find anything against showering with saltwater by skimming the results of a naive google search.
  - maxerickson 9y ago
    You can get about the same effect by running the water to get wet, turning it off while washing and then back on for rinsing (the infamous "navy shower"). I imagine the biggest strike against showering with salt water is that you'd need treatment, supply and heating dedicated to the salt tap. And then the salt water is busy corroding all the infrastructure devoted to it.
    - dhimes 9y ago
      Turning off the shower while I am soaping is now second-nature to me, like turning off the water while brushing teeth. I highly recommend it.
      - glenneroo 9y ago
        Going even further, I switched early last year to not using soap at all (except for extreme dirt which warm water couldn't remove) and my showers are done in 1-3 minutes (depending if I wash my hair or not). My girlfriend also says I smell better (and not like various soaps). Also related, a chemical engineer from MIT started a company[0] back in 2013 purporting that showering kills our healthy bacteria. Supposedly he hasn't showered in 13 years, although their latest product recommends "rinsing in the shower for 3 minutes" followed by spraying their product on your body. [0]http://aobiome.com http://aobiome.com
        goda90 9y ago
        How much do you exercise? I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria.
        com2kid 9y ago
        > I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria. As someone who spends ~3 hours a day doing vigorous exercise, there is no way this is true. I smell awful afterwards.
        goda90 9y ago
        But how do you smell after you shower it off? It could also be that people who exercise a lot might be less likely to sweat outside of exercise time.
        com2kid 9y ago
  - tdb7893 9y ago
    Can you use fresh and saltwater in the same pipes? I feel like they would need to stay separate and having all the infrastructure duplicated and appliances able to switch between the two sounds expensive.
    - oftenwrong 9y ago
      In HK there is a separate water system for sea water, and homes that use it for flushing toilets do have a second set of pipes. The additional cost of this complexity must be weighed against the value of having enough clean water for daily life.
  - unethical_ban 9y ago
    The trick is disposing of the saltwater. Consider that depending on the locale, wastewater might be put back into the water table or else treated for bacteria then let back into the environment. Saltwater saturating our soils, water table or even being too concentrated in a bay would affect the ecosystem negatively. Source: Someone who isn't an expert in waste management or ecology.
- stult 9y ago
  Wouldn't salt water in toilets require two sets of pipes leading into each home? Seems like an expensive proposition unless you're building a new community from scratch.
  - Jedd 9y ago
    It does, but it isn't. Similarly multiple out-going pipes to split off various levels of grey waste (some direct to garden, others, to soakways, or to septic processing systems). Capex for these kinds of systems is ultimately dwarfed by savings on opex - just like we find with mandatory double-glazing & other insulation regulations.
    - nerdponx 9y ago
      Makes sense. But out of curiosity, where are you getting that info? Personal experience? Research in some field?
      - Jedd 9y ago
        Mostly personal experience including some stories from permaculture types who've been approaching these problems for a while. I'm designing a habitat that will have an additional complication of both low-pressure gravity fed and electric-pump (city pressure) circuits. Regulations lag behind optimum configuration, though parts of EU, especially in the north, legislated triple-glazing (f.e.) quite a few years ago (can't find a cost analysis of break-even points, unfortunately). I'm sure there's plenty of assumptions wrapped up in these regulations around estimated abode longevity, energy pricing over that period, etc. But as to multiple water sources into abodes, I haven't seen much formal work on it. I think the idea gets touted in London periodically - it'd be a nice solution to the dual problems of high water table and (surprisingly) occasional potable water shortages. But retrofitting this to an existing, massive, badly planned metropolis would be a nightmare.
  - Shivetya 9y ago
    Well at the commercial level we certainly could and it has been done though most of the uses I have seen are to golf courses and certain parks. certainly large commercial buildings could have a separate set of pipes to provide toilets with water. now what should be more easily done is require building codes to insure large complexes have separate gray and black water pipes so that easier to treat water is routed better.
- thatwebdude 9y ago
  We (as a society) really need to be pushing more efficient water appliances. I looked up liters to gallons since I'm backwards and - in case anyone else is too - 10 liters is ~2.5 gallons. I replaced three toilest in my home that were flushing ~4 gallons with each flush with ones that flush with 1.28 gallons now. They are much more powerful than the previous ones I had, and use (liter-wise) less than half of the 10-liter mark. Do your efficient toilets overseas not get down to the 4-6 liter range per flush? The switch to more efficient toilets really made a big impact on my water bill for barely a dent to the wallet.
  - jacquesm 9y ago
    How much do you pay for water? Did you calculate the pay-back time of those new toilets?
    - refurb 9y ago
      Just as a reference point, in SF, the first three "units" of water (748 gallons), costs $6.42/unit. Or $0.009 per gallon. After that, $0.011 per gallon. That doesn't include things like delivery fees, sewer charges, etc.
    - thatwebdude 9y ago
      No idea. I'm more about less waste though, so that and the home renovation was what sold me. Self-install so the cost was relatively low. http://www.hcsa.us/files/What-does-my-toilet-really-cost-me.pdf http://www.hcsa.us/files/What-does-my-toilet-really-cost-me....
  - nsxwolf 9y ago
    Newer toilets in the US are only allowed 6 liters max.
    - logfromblammo 9y ago
      And those toilets can never seem to handle my #2s. You're not saving anything if you have to flush 2-3 times and use a plunger every time. Regulating the volume of the tank is useless unless you also define a test standard for functionality. It's like saying that cars have to meet a minimum mileage standard without also specifying that they have to be able to maintain 60 mph while going up a 10% grade. Except in that situation, cars that do not meet the implicit minimum consumer standard don't get purchased off the lot. In houses, the person who buys the toilet is more likely planning to repackage it into an entire house and resell it to someone else than use it personally. So your toilet might look like a full-sized sedan, but have a go-kart engine under the hood. They just bolted a smaller tank onto a base that was designed for a larger flush volume. So what those toilets are allowed de jure is not necessarily lowering de facto water use. Yes, there are toilets out there that were redesigned for low flush volumes, and they do save water, but they have not displaced the letter-of-the-law, flush-it-twice toilets in the construction of cut-every-possible-corner suburban subdivisions.
- e12e 9y ago
  If you have plentiful access to salt water, it might be worth it to use that for "black water" (sewage).
tolien 9y ago
Most of that 1.3M litres is presumably going to be within a 12 hour period, surely? Whether it’s for human use (drinking, washing, flushing) or agriculture. I guess you can produce constantly and store - a quick search suggests that 1.3M litres would barely be known to a reservoir but you wouldn’t have to worry about the seasonality of rainfall. Yeah, seems feasible. Almost too good to be true…
smoyer 9y ago
We were each producing drinking water ... "We require" is probably a bit strong - LiveStrong says the average male needs 13 cups of water each day. If you add in the amount of water we use based on our life-style, then I can believe 130l.
peteretep 9y ago
> We require 130 litres / person > per day in Europe We don't require 130 litres of potable water though, which is what this produces. Salt water's fine for washing, brushing teeth, flushing toilets, washing hands, and so on.
torrent-of-ions 9y ago
What does this 130 litres include? Food? Meat? Clothes?
LeifCarrotson 9y ago
It's 6 liters per square meter of solar membrane. They increased it 25x with a Fresnel lens. From the paper: > For NEMD experiments with solar concentration, a 25.4 × 25.4 cm Fresnel lens was used to concentrate sunlight on the membrane surface by a factor of 25. The unconcentrated and concentrated solar intensities at the NESMD module surface were 0.7 and 17.5 kW·m−2, respectively. A facility of 500x500 m^2 would probably still be feasible. The link is to the university news department, the actual paper is here: http://www.pnas.org/content/early/2017/06/14/1701835114.full http://www.pnas.org/content/early/2017/06/14/1701835114.full or here in PDF format: http://www.pnas.org/content/early/2017/06/14/1701835114.full.pdf http://www.pnas.org/content/early/2017/06/14/1701835114.full...
- Retric 9y ago
  You can only concentrate sunlight for a fraction of the time. The good news is water is easy to store for long periods, the bad news is utilization is very low. Sierra Suntower https://en.wikipedia.org/wiki/Sierra_SunTower https://en.wikipedia.org/wiki/Sierra_SunTower is kind of a worst case senario but they got about 100 hours per year of operation.
  - jacquesm 9y ago
    1620 MWh of output over several years? They'd be better off using the fuel used to construct it directly. Amazing that that particular project got so much praise before the numbers were in. I've played around with solar concentrators in the early 00's and realized very quickly that it wasn't worth my time due to all kinds of practical constraints, I always wondered why the companies and organizations that build these things don't do a scale model first. That way at least you get some real world data to plug into your spreadsheet before spending big $.
ccalvert 9y ago
If this desalination system allowed a city to generate even 50% of their water needs, that would be a significant step forward. I keep seeing this metric put forward: Does X generate 100% of the needed water/electricity/heat. Why does it have to 100%? Can't three systems each contributing 33.3% be enough to reach 100%? Our household solar power installation here in the very rainy Seattle area generates 98.15% of our electric power needs, including that for our electric car. I wish it were 100%, and if the sun shines for a few days in a row, sometimes it does generate 100% of our electric power needs for the last 365 days. It is, however, much better to meet 98% of our needs that to meet none of our needs.
- ivankirigin 9y ago
  To hit that rate you need energy storage at your house, right? In the context of grid power, that's an even bigger issue given cost and pollution from base load generators.
- kayfox 9y ago
  Or three systems capable of producing more than 50%. Because infrastructure should have redundancy.
  - clock_tower 9y ago
    Five systems generating 33.3%, then. He's got a very valid point.
ivankirigin 9y ago
Presumably you'd need to generate 1.3M liters off of only daylight hours, making it more like 130m*130m per 10K people. Cairo has a population density of 18K people per km2, so this would mean covering 2% of the area. For contrast, streets and parking take up ~40% of most US cities.

Kayou 9y ago

I thought 130 litres/person was quiet high and probably included things like water to grow vegetables, but no, one shower is between 30 et 50 litres and each time you go to the bathroom, it's 10 litres of drinkable water. Of course, I you have saltwater and no freshwater, you would probably use saltwater in your toilets, so that could reduce the daily usage of at least 20 litres. But then, if you consider agriculture and manufacturing, I guess that the number of 130litres/person would blow up completely.

positivecomment 9y ago
Maybe people can also shower with saltwater followed by a quick rinse in drinkable water. That would reduce the usage drastically. I couldn't find anything against showering with saltwater by skimming the results of a naive google search.
- maxerickson 9y ago
  You can get about the same effect by running the water to get wet, turning it off while washing and then back on for rinsing (the infamous "navy shower"). I imagine the biggest strike against showering with salt water is that you'd need treatment, supply and heating dedicated to the salt tap. And then the salt water is busy corroding all the infrastructure devoted to it.
  - dhimes 9y ago
    Turning off the shower while I am soaping is now second-nature to me, like turning off the water while brushing teeth. I highly recommend it.
    - glenneroo 9y ago
      Going even further, I switched early last year to not using soap at all (except for extreme dirt which warm water couldn't remove) and my showers are done in 1-3 minutes (depending if I wash my hair or not). My girlfriend also says I smell better (and not like various soaps). Also related, a chemical engineer from MIT started a company[0] back in 2013 purporting that showering kills our healthy bacteria. Supposedly he hasn't showered in 13 years, although their latest product recommends "rinsing in the shower for 3 minutes" followed by spraying their product on your body. [0]http://aobiome.com http://aobiome.com
      - goda90 9y ago
        How much do you exercise? I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria.
        com2kid 9y ago
        > I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria. As someone who spends ~3 hours a day doing vigorous exercise, there is no way this is true. I smell awful afterwards.
        goda90 9y ago
        But how do you smell after you shower it off? It could also be that people who exercise a lot might be less likely to sweat outside of exercise time.
        com2kid 9y ago
- tdb7893 9y ago
  Can you use fresh and saltwater in the same pipes? I feel like they would need to stay separate and having all the infrastructure duplicated and appliances able to switch between the two sounds expensive.
  - oftenwrong 9y ago
    In HK there is a separate water system for sea water, and homes that use it for flushing toilets do have a second set of pipes. The additional cost of this complexity must be weighed against the value of having enough clean water for daily life.
- unethical_ban 9y ago
  The trick is disposing of the saltwater. Consider that depending on the locale, wastewater might be put back into the water table or else treated for bacteria then let back into the environment. Saltwater saturating our soils, water table or even being too concentrated in a bay would affect the ecosystem negatively. Source: Someone who isn't an expert in waste management or ecology.
stult 9y ago
Wouldn't salt water in toilets require two sets of pipes leading into each home? Seems like an expensive proposition unless you're building a new community from scratch.
- Jedd 9y ago
  It does, but it isn't. Similarly multiple out-going pipes to split off various levels of grey waste (some direct to garden, others, to soakways, or to septic processing systems). Capex for these kinds of systems is ultimately dwarfed by savings on opex - just like we find with mandatory double-glazing & other insulation regulations.
  - nerdponx 9y ago
    Makes sense. But out of curiosity, where are you getting that info? Personal experience? Research in some field?
    - Jedd 9y ago
      Mostly personal experience including some stories from permaculture types who've been approaching these problems for a while. I'm designing a habitat that will have an additional complication of both low-pressure gravity fed and electric-pump (city pressure) circuits. Regulations lag behind optimum configuration, though parts of EU, especially in the north, legislated triple-glazing (f.e.) quite a few years ago (can't find a cost analysis of break-even points, unfortunately). I'm sure there's plenty of assumptions wrapped up in these regulations around estimated abode longevity, energy pricing over that period, etc. But as to multiple water sources into abodes, I haven't seen much formal work on it. I think the idea gets touted in London periodically - it'd be a nice solution to the dual problems of high water table and (surprisingly) occasional potable water shortages. But retrofitting this to an existing, massive, badly planned metropolis would be a nightmare.
- Shivetya 9y ago
  Well at the commercial level we certainly could and it has been done though most of the uses I have seen are to golf courses and certain parks. certainly large commercial buildings could have a separate set of pipes to provide toilets with water. now what should be more easily done is require building codes to insure large complexes have separate gray and black water pipes so that easier to treat water is routed better.
thatwebdude 9y ago
We (as a society) really need to be pushing more efficient water appliances. I looked up liters to gallons since I'm backwards and - in case anyone else is too - 10 liters is ~2.5 gallons. I replaced three toilest in my home that were flushing ~4 gallons with each flush with ones that flush with 1.28 gallons now. They are much more powerful than the previous ones I had, and use (liter-wise) less than half of the 10-liter mark. Do your efficient toilets overseas not get down to the 4-6 liter range per flush? The switch to more efficient toilets really made a big impact on my water bill for barely a dent to the wallet.
- jacquesm 9y ago
  How much do you pay for water? Did you calculate the pay-back time of those new toilets?
  - refurb 9y ago
    Just as a reference point, in SF, the first three "units" of water (748 gallons), costs $6.42/unit. Or $0.009 per gallon. After that, $0.011 per gallon. That doesn't include things like delivery fees, sewer charges, etc.
  - thatwebdude 9y ago
    No idea. I'm more about less waste though, so that and the home renovation was what sold me. Self-install so the cost was relatively low. http://www.hcsa.us/files/What-does-my-toilet-really-cost-me.pdf http://www.hcsa.us/files/What-does-my-toilet-really-cost-me....
- nsxwolf 9y ago
  Newer toilets in the US are only allowed 6 liters max.
  - logfromblammo 9y ago
    And those toilets can never seem to handle my #2s. You're not saving anything if you have to flush 2-3 times and use a plunger every time. Regulating the volume of the tank is useless unless you also define a test standard for functionality. It's like saying that cars have to meet a minimum mileage standard without also specifying that they have to be able to maintain 60 mph while going up a 10% grade. Except in that situation, cars that do not meet the implicit minimum consumer standard don't get purchased off the lot. In houses, the person who buys the toilet is more likely planning to repackage it into an entire house and resell it to someone else than use it personally. So your toilet might look like a full-sized sedan, but have a go-kart engine under the hood. They just bolted a smaller tank onto a base that was designed for a larger flush volume. So what those toilets are allowed de jure is not necessarily lowering de facto water use. Yes, there are toilets out there that were redesigned for low flush volumes, and they do save water, but they have not displaced the letter-of-the-law, flush-it-twice toilets in the construction of cut-every-possible-corner suburban subdivisions.
e12e 9y ago
If you have plentiful access to salt water, it might be worth it to use that for "black water" (sewage).

tolien 9y ago

Most of that 1.3M litres is presumably going to be within a 12 hour period, surely? Whether it’s for human use (drinking, washing, flushing) or agriculture. I guess you can produce constantly and store - a quick search suggests that 1.3M litres would barely be known to a reservoir but you wouldn’t have to worry about the seasonality of rainfall. Yeah, seems feasible. Almost too good to be true…

smoyer 9y ago

We were each producing drinking water ... "We require" is probably a bit strong - LiveStrong says the average male needs 13 cups of water each day. If you add in the amount of water we use based on our life-style, then I can believe 130l.

peteretep 9y ago

> We require 130 litres / person > per day in Europe We don't require 130 litres of potable water though, which is what this produces. Salt water's fine for washing, brushing teeth, flushing toilets, washing hands, and so on.

torrent-of-ions 9y ago

What does this 130 litres include? Food? Meat? Clothes?

LeifCarrotson 9y ago

It's 6 liters per square meter of solar membrane. They increased it 25x with a Fresnel lens. From the paper: > For NEMD experiments with solar concentration, a 25.4 × 25.4 cm Fresnel lens was used to concentrate sunlight on the membrane surface by a factor of 25. The unconcentrated and concentrated solar intensities at the NESMD module surface were 0.7 and 17.5 kW·m−2, respectively. A facility of 500x500 m^2 would probably still be feasible. The link is to the university news department, the actual paper is here: http://www.pnas.org/content/early/2017/06/14/1701835114.full http://www.pnas.org/content/early/2017/06/14/1701835114.full or here in PDF format: http://www.pnas.org/content/early/2017/06/14/1701835114.full.pdf http://www.pnas.org/content/early/2017/06/14/1701835114.full...

Retric 9y ago
You can only concentrate sunlight for a fraction of the time. The good news is water is easy to store for long periods, the bad news is utilization is very low. Sierra Suntower https://en.wikipedia.org/wiki/Sierra_SunTower https://en.wikipedia.org/wiki/Sierra_SunTower is kind of a worst case senario but they got about 100 hours per year of operation.
- jacquesm 9y ago
  1620 MWh of output over several years? They'd be better off using the fuel used to construct it directly. Amazing that that particular project got so much praise before the numbers were in. I've played around with solar concentrators in the early 00's and realized very quickly that it wasn't worth my time due to all kinds of practical constraints, I always wondered why the companies and organizations that build these things don't do a scale model first. That way at least you get some real world data to plug into your spreadsheet before spending big $.

ccalvert 9y ago

If this desalination system allowed a city to generate even 50% of their water needs, that would be a significant step forward. I keep seeing this metric put forward: Does X generate 100% of the needed water/electricity/heat. Why does it have to 100%? Can't three systems each contributing 33.3% be enough to reach 100%? Our household solar power installation here in the very rainy Seattle area generates 98.15% of our electric power needs, including that for our electric car. I wish it were 100%, and if the sun shines for a few days in a row, sometimes it does generate 100% of our electric power needs for the last 365 days. It is, however, much better to meet 98% of our needs that to meet none of our needs.

ivankirigin 9y ago
To hit that rate you need energy storage at your house, right? In the context of grid power, that's an even bigger issue given cost and pollution from base load generators.
kayfox 9y ago
Or three systems capable of producing more than 50%. Because infrastructure should have redundancy.
- clock_tower 9y ago
  Five systems generating 33.3%, then. He's got a very valid point.

ivankirigin 9y ago

Presumably you'd need to generate 1.3M liters off of only daylight hours, making it more like 130m*130m per 10K people. Cairo has a population density of 18K people per km2, so this would mean covering 2% of the area. For contrast, streets and parking take up ~40% of most US cities.