# Water Resources Q

**URL:** <https://boards.straightdope.com/t/water-resources-q/664352>\
**Category:** Factual Questions\
**Created:** [July 24, 2013, 2:41am UTC](https://boards.straightdope.com/t/water-resources-q/664352 "2013-07-24T02:41:20Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Horatio\_Hellpop](https://avatars.discourse-cdn.com/v4/letter/h/e5b9ba/32.png) [@Horatio\_Hellpop](https://boards.straightdope.com/u/Horatio_Hellpop)\
**Post date:** [July 24, 2013, 2:41am UTC](https://boards.straightdope.com/t/water-resources-q/664352/1 "2013-07-24T02:41:20Z")

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I keep hearing about processes for turning raw sewage into drinkable tap water, most recently in [Santa Clara, CA](http://sanfrancisco.cbslocal.com/2013/07/22/toilet-to-tap-water-purification-coming-to-south-bay/). I could see why this would be a boon to, say, the International Space Station or someplace in the middle of a desert, but why can’t Santa Clara–on San Francisco Bay–use a similar process to get drinking water from the sea? Is salt trickier to get rid of than raw sewage? Why would the process work on one and not the other?

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**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\
**Post date:** [July 24, 2013, 2:50am UTC](https://boards.straightdope.com/t/water-resources-q/664352/2 "2013-07-24T02:50:31Z")

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It’s my understanding that desalinization is very expensive and requires _a lot_ of energy, which is what you need to do if you wanted to drink ocean water.

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**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\
**Post date:** [July 24, 2013, 2:52am UTC](https://boards.straightdope.com/t/water-resources-q/664352/3 "2013-07-24T02:52:20Z")

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sea water is very concentrated with the worst possible type of contaminant, ionic atoms. It should be more expensive to clean that up than anything else.  
The process is reverse-osmosis, which uses electrical power to drive the ions out.

Sewerage is only slightly contaminated with life forms and at worst molecules to start with … these can be settled out and micro-filtered , which doesn’t consume power to operate (as long as the water flows through the filter… )

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**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\
**Post date:** [July 24, 2013, 2:53am UTC](https://boards.straightdope.com/t/water-resources-q/664352/4 "2013-07-24T02:53:27Z")

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From [here](http://en.wikipedia.org/wiki/Desalination) it looks like it costs about fifty cents to dollar per 265 gallons on top of cleaning it. So if you can _just_ clean it, that’s going to save quite a bit of money.