# Where do islands get their water? **URL:** \ **Category:** Factual Questions\ **Created:** [August 1, 2005, 2:58pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142 "2005-08-01T14:58:28Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![tdn](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@tdn](https://boards.straightdope.com/u/tdn)\ **Post date:** [August 1, 2005, 2:58pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/1 "2005-08-01T14:58:28Z")
I just got back from my vacation to Martha’s Vineyard, and I have to wonder–where do islands like that get fresh water? That particular island is a good 5 miles from the mainland, and both it and that part of the mainland are primarily made of sand. I imagine that it would be hard to dig wells into sucha sandy location. And there are no mountains to speak of, so spring water wouldn’t be used. It can’t be shipped in, as the sheer volume would be prohibitive. Here’s a clue: Some roads have signs saying “Freshwater collection area”, which is a cryptic way of saying to not salt icy roads. But where would they collect it from? It’s all salt marsh. ---
**Author:** ![Patty\_O\_Furniture](https://avatars.discourse-cdn.com/v4/letter/p/96bed5/32.png) [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)\ **Post date:** [August 1, 2005, 3:07pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/2 "2005-08-01T15:07:46Z")
Rain? ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [August 1, 2005, 3:15pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/3 "2005-08-01T15:15:04Z")
My WAG: If you dig down deep enough, you’ll get freshwater. And with today’s drilling technologies, it doen’t realyl matter what the soil is made of. ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [August 1, 2005, 3:16pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/4 "2005-08-01T15:16:00Z")
From [here](http://64.233.161.104/search?q=cache:l39jUSBBuI4J:www.vineyardconservationsociety.org/newsletters/spring04.qxd-tp.pdf+marthas+vineyard+aquifer&hl=en) At a depth about 70 feet below sea level is an aquifer consisting of bands of water bearing sand and gravel. About 145 billion gallons of it, with 12% being recharged annually (I assume by rain and snow melt). ---
**Author:** ![tdn](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@tdn](https://boards.straightdope.com/u/tdn)\ **Post date:** [August 1, 2005, 3:20pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/5 "2005-08-01T15:20:19Z")
> [@Finagle](#): > > From [here](http://64.233.161.104/search?q=cache:l39jUSBBuI4J:www.vineyardconservationsociety.org/newsletters/spring04.qxd-tp.pdf+marthas+vineyard+aquifer&hl=en) > > At a depth about 70 feet below sea level is an aquifer consisting of bands of water bearing sand and gravel. About 145 billion gallons of it, with 12% being recharged annually (I assume by rain and snow melt). Thanks for that. Good answer. It seems that there is some effort to conserve water. I saw a lot of signs that said “Voluntary water ban in effect.” Voluntary, Gracie? ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [August 1, 2005, 10:20pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/6 "2005-08-01T22:20:21Z")
> [@tdn](#): > > Thanks for that. Good answer. > > It seems that there is some effort to conserve water. I saw a lot of signs that said “Voluntary water ban in effect.” Voluntary, Gracie? Probably “voluntary” in the way paying the IRS is “voluntary.” It only means they count on you to do your part without having to send out the tax collector. As soon as you fail to volunteer, well, then it’s no longer voluntary. 😉 ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [August 1, 2005, 10:25pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/7 "2005-08-01T22:25:33Z")
Why is the water not salty there? I was just in St Augustine Florida visiting the old fort which is righ on the bay but there were freshwater wells within the walls. ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [August 1, 2005, 11:38pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/8 "2005-08-01T23:38:41Z")
> [@Patty O'Furniture](#): > > Rain? Very small rocks? ---
**Author:** ![fighting\_ignorant](https://avatars.discourse-cdn.com/v4/letter/f/ac8455/32.png) [@fighting\_ignorant](https://boards.straightdope.com/u/fighting_ignorant)\ **Post date:** [August 1, 2005, 11:44pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/9 "2005-08-01T23:44:04Z")
> [@Cervaise](#): > > Very small rocks? Witches? ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [August 2, 2005, 2:42am UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/10 "2005-08-02T02:42:01Z")
- - - On an island you can dig down into the ground stopping before you reach the actual sea level, and there is fresh water “floating” on top of the supply of salty water. Normally you dig places with lots of plants, because most plants aren’t real tolerant of salty water, so that’s a clue. ~ ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [August 2, 2005, 3:15am UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/11 "2005-08-02T03:15:21Z")
Some islands rely on desalinization plants for their water. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 2, 2005, 3:32am UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/12 "2005-08-02T03:32:26Z")
Last year’s tsunami caused big problems for many small islands, when seawater filtered down into the fresh water supplies: > [@](#): > > Thirteen islands had to be completely abandoned as all the buildings and infrastructure were smashed and fresh water sources contaminated by the sea. [Maldives recover from tsunami](http://www.un.org/apps/news/story.asp?NewsID=13290&Cr=tsunami&Cr1=) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 2, 2005, 4:18am UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/13 "2005-08-02T04:18:41Z")
> [@Padeye](#): > > Why is the water not salty there? I was just in St Augustine Florida visiting the old fort which is righ on the bay but there were freshwater wells within the walls. Saltwater is denser than freshwater, so that the freshwater deposited on the island as rain will “float” as a lens over the salt water without mixing too much. If too much freshwater is removed, the saltwater will intrude into the island’s aquifer. More on seawater intrusion [here](http://pud.co.jefferson.wa.us/Seawater_Intrusion.htm). ---
**Author:** ![jeffq](https://avatars.discourse-cdn.com/v4/letter/j/c68b51/32.png) [@jeffq](https://boards.straightdope.com/u/jeffq)\ **Post date:** [June 3, 2016, 10:22pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/14 "2016-06-03T22:22:30Z")
The seawater intrusion link above is broken. Here’s an archived version: More on [seawater intrusion](http://web.archive.org/web/20080328021415/http://pud.co.jefferson.wa.us/Seawater_Intrusion.htm). ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [June 3, 2016, 10:48pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/15 "2016-06-03T22:48:19Z")
At high tide, I live on a three acre island. I have a fresh water well less than 100 feet from the ocean. There is enough fresh water for two houses. Being flat, like Martha’s Vineyard, has advantages. The water tends to soak into the ground rather than runoff into the ocean. ---
**Author:** ![Hazle\_Weatherfield](https://avatars.discourse-cdn.com/v4/letter/h/e9bcb4/32.png) [@Hazle\_Weatherfield](https://boards.straightdope.com/u/Hazle_Weatherfield)\ **Post date:** [June 3, 2016, 10:49pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/16 "2016-06-03T22:49:51Z")
Can zombies swim?🙂 ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [June 3, 2016, 11:29pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/17 "2016-06-03T23:29:21Z")
> [@mks57](#): > > Some islands rely on desalinization plants for their water. Concrete rain catchment basins (look kind of like a raised, sloping parking lot) are also seen, like one per neighborhood, e.g. on smallish Caribbean\* islands (especially because there’s a rainier season and a drier season). \*Where the original zombies come from ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [June 4, 2016, 6:55am UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/18 "2016-06-04T06:55:25Z")
I was stationed at a LORAN station on San Salvador, Bahamas for a year. We had a rain catchment and wells for fresh water. Our Corpsman did a daily check on the water in the “day” tank to make certain it was safe for drinking. And we only were permitted to take “sea showers”\*. \*sea shower = 1) Turn on the shower and get wet all over. B) Turn off the water, soap up, and scrub. III) Turn on the shower and rinse off. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [June 4, 2016, 3:45pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/19 "2016-06-04T15:45:34Z")
An extreme example of an island you wouldn’t guess has “fresh” water is [Clipperton](https://en.wikipedia.org/wiki/Clipperton_Island) in the Pacific. A thin, virtually barren atoll surrounding a large lagoon. Yet the lagoon is ~fresh water. All supplied by rain in the middle of nowhere. The excess of rainfall rate over evaporation rate is quite small, but big enough over long periods of time. ---
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [June 4, 2016, 3:51pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/20 "2016-06-04T15:51:20Z")
> [@jeffq](#): > > The seawater intrusion link above is broken. Here’s an archived version: > > More on [seawater intrusion](http://web.archive.org/web/20080328021415/http://pud.co.jefferson.wa.us/Seawater_Intrusion.htm). So, you sign up back in 2003, never comment for 13 years and now you make your first comment? howwhatwhy? [Next page](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142.md?page=2)