environment

Desalinating seawater sounds easy, but there are more sustainable ways to meet people's water needs

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By Gregory Pierce

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Very good article and very true. I wish the authors could have put prices on water from the sources mentioned to show how much more expensive it is to desalinate water. Not mentioned is the cost to pump water uphill from the coast to regions further inland. The city limits of Los Angeles extend from sea level to over 1200 meters elevation. Most of LA is currently fed by gravity from reservoirs that more than sit 300 meters above sea level. Pumping desalinated water up hill to the city's many reservoirs located in the mountains around LA would be very costly.

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quote: The first and relatively cheapest way to address water shortages is by using less.

Although quick to implement, it is also the least reliable and most politically damaging. The use of water meters punishes the poor and those who are trying to grow their own food, whilst rich people are free to waste as much as they want.

Stopping leaks from pipes rapidly would save a great deal of water. More reservoirs, a national water grid and better trapping of storm water are good. Recycling waste water for drinking makes people uncomfortable as system failures (which are quite common) would be particularly unpleasant.

Reservoirs require the compulsory purchasing of land, which can take time and be unpopular. It also trashes archaeology and destroys both wild environments and productive farmland.

Re-use of grey water is hampered by the design of properties. Household plumbing was never designed to conserve washing-up water and bath water, and kitchen sinks are often a bit low to use gravity.

Any alterations to peoples' homes would get a limited roll out, as in countries like the UK, there is widespread aversion to employing (largely unregulated) tradesmen. It is easier to demand specific design features in the builder's regs for new homes.

We can also save a lot more water in agriculture using systems like drip feed irrigation. An interesting gardening option that might be scaled up appeared on TV here tonight, using unglazed pottery (which is permeable) as a way to distribute water with less evaporative waste. In gardens, plants do not need anything like as much water as you might think, once they are established. Spot-watering with a watering can and growing plants 'hard' is better than using a hosepipe, which is very wasteful at any time of the year.

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I agree with the author of this post. I lived in Saipan for 10 years and struggled with water all that time. Most homes have cisterns there that hold rainwater captured from the roof which helped a great deal. I would say that my community water usage was less than half after installing a cistern underground. In the future, we could cut water usage by 75% by requiring cisterns for private and commercial businesses as well as restricting water usage for landscaping and by utilizing local plants for this purpose.

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I disagree with this article. I refer those interested to an article in the July 29, 2016 issue of Scientific American magazine. The article basically states that Israeli innovations in the field of desalination are groundbreaking, and make it more affordable than many of the currently used systems for moving freshwater over many hundreds of miles, and more sustainable than using up scarce groundwater supplies.

Regarding the article:

"Killing aquatic life" That claim is so absurd it doesn't even need to be addressed.

"Unaffordable water from costly plants" If one bothers to look at the facts presented in the Scientific American article, one sees that the Israelis currently pay less for unit of water than do urban consumers in Los Angeles. Given that fully 20% of all the electricity used in California goes towards moving water from north to south, over mountains, I do not find that claim hard to understand. Switching to desalinated water would save money for the people of Southern California.

Desalinated water is not today practical for California's farmers, because they are used to getting their water at below cost, subsided by taxpayers. It isn't that California's farmers could not adapt to using desalinated water, but that as long as they get cheap water they are not incentivized to make any changes.

I would also point out that a typical family in San Diego, who recently switched to desalinated water, pay an average of $5 US more per month than they did before. That seems a reasonable tradeoff to be guaranteed a steady supply of fresh water.

As for Conservation and Reuse, one can only get so far by economizing. At some point one has to address the underlying issue of a shortage of fresh water.

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Desalination plants discharge brine and wastewater, which can also kill nearby aquatic life if the process is not done properly.

But if done properly there is no iisue of this nature.

And generating the large quantity of energy that the plants consume has its own environmental impacts until it can be done carbon-free, which is still years off in most cases.

It can be done carbon free now if all plants were constructed with their own solar/wind power generation, which can be diverted back to the main grid when the plants are not in operation.

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But if done properly there is no iisue of this nature.

Where is the edit button? But if done properly there is no issue of this nature.

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It can be done carbon free now if all plants were constructed with their own solar/wind power generation, which can be diverted back to the main grid when the plants are not in operation.

To use solar to power a desalinization plant sufficient to meet the needs of a county the size and population of Los Angeles County would require the wholesale removal of vast residential and business tracts to site the necessary solar panels. LA County is just under 10 million people with elevations ranging from sea level to over 3000 meters. Now if you want to desalinize water for a megalopolis the size of Tokyo you would need to build a vast island in Tokyo Bay for sufficient solar panels. This idea that one can desalinize water on the scale necessary for places like Tokyo, Shanghai or LA using solar power is simply risible. How much of your existing city are you willing to scrape off the ground to site solar panels? We have huge arguments now about the negative effects of using the desert for solar arrays. The desert is a surprisingly fragile ecosystem. Covering empty lands far from cities with solar arrays is not going to go far either. Israel is a tiny country with a tiny population. You could loose Israel in LA County. Israel doesn't scale up to the vastness and huge population of a place like California, or China.

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A 5MW solar farm requires 500,000 square feet of land, or 11.5 acres. The desalinization plant in Carlsbad California requires 38 MW of power to produce 50 million gallons, or 153 acre feet, of fresh water per day or 56,000 acre feet per year if the plant works at full capacity every day. The solar farm to power this thing would have to be 88 acres. Now consider that LA MWD ships about 1.5 million acre feet per year of water to their customers. You would need 30,000 desal plants the size of the one in Carlsbad and they would consume 1.14 million MW of power. To produce that much power you would need 7.8 million acres of land covered in PV arrays. And that is just to power desalinization. The Central Valley of California is about 7 million acres and to power this notional desal scheme one would have to cover 1.5 million acres of land with PV. Just for desal and nothing else. The whole idea is simply ridiculous.

As it stands LA is going to cut its use of imported water by half through use of waste water purified to a potable standard at half the price per acre foot of desalinated water, and purifying water from a highly contaminated aquifer. Being able to use the aquifer will allow the city to fully use a decades old system of spreading basins where storm water is captured and diverted into shallow basins and allowed to percolate back into the aquifer. To maximize the use of the spreading basins some old dams have been rebuilt to modern seismic standards so they can safely retain a full pool after major storms and gradually meter the stored water out into the spreading basins to percolate back into the aquifer. The city is also building methods to capture storm water run off in the city and divert it to spreading basins. Desal is truly a costly last resort that most regions of the world do not need.

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