why isn’t ocean water filtered and used when somewhere is having a water crisis?
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Why is desalination so expensive?
Salt is a very tiny molecule. You might know its chemical name is NaCl. That means it’s just 1 atom of sodium (Na) and 1 atom of chlorine (Cl). A molecule of salt is only a little bit bigger than a water molecule.
In order to get the salt out of the water, you have two options, and both a very expensive. One option is to basically boil the water and collect the steam. Another option is to use a filter with very, very tiny holes. This also takes a lot of energy because you have to push the water through the filter. With most filters, water flows through pretty easily. But the special filters needed to separate out the teeny tiny salt molecules are super-fine, so you need a lot of pressure to push the water through.
It is. The Australian Defence Force has at least a couple of reverse osmosis units that it uses on humanitarian deployments.
>ELI5 why isn’t ocean water filtered and …
Being a bit pedantic, but it’s not filtration. Filters remove suspended solid particles, sediment, sand. The salt is dissolved, so you’re trying to remove a liquid (dissolved salt ) from another liquid (water).
The options are distillation or reverse osmosis. Distillation obviously uses a lot of energy to boil off and recondense the water. Reverse osmosis is cheaper, but still uses a lot of energy.
I once operated a small RO system, part of a plant to produce deionized (very pure) water from mains water. The RO pumps were multi-stage high pressure pumps, about 6′ tall. A lot of electricity was needed; much $$$.
Always had the dream that excess solar power could be used to desalinate, rather than the power grid owners whinge about rooftop solar destroying their business. Unfortunately the reality is it probably wont be consistent enough for a meaningful supply… but for places like western Australian and California it would be ideal!
Sydney, Australia has a desalination plant, and even when it’s not needed it is required to run to keep working.
Also the resulting brine is highly concentrated salt water and can destroy the surrounding ecosystem. We just dump that back into the ocean
California has and uses desalination plants. We just don’t have enough. As others have said it isn’t feasible to solve a water crisis with desalination due to energy requirements.
It is! Desalination is used extensively in truly water-scare places, like Israel, Saudi Arabia, Western Australia, etc. However, these systems do have some challenges, political, environmental, and practical.
First, the political. Desalination plants are large, expensive projects which take a long time to build, and a longer time to plan and approve. The conditions which are creating your water crisis may not be around by the time your project is built, eroding public support for them.
Second, the environmental. Desalination, even assuming you can get the energy from renewable sources, is not without environmental impact. You’re sucking up massive amounts of water, filtering some of it out as clean, drinkable water, and flushing the rest out back into the ocean at a higher salinity than you took in. At the inlet, you’re sucking up and crushing lots of different types of ocean live, and at the outlet, you’re dumping a flow of water which may be harmful to the species near to your shore.
Finally, the practical. Having a giant tank full of filtered water right at the shoreline may not actually suit the purposes of your water demand. For example, 75% of California’s water demand is driven by agriculture, which is (generally) far inland of any body of water which could conceivably be treated. How, exactly are you going to get it there? Operating pumps along huge pipelines adds yet another tremendous expense to your water project, concomitant with obtaining it.
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