# 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:** 7\ **Page:** 2
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 4, 2016, 4:38pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/21 "2016-06-04T16:38:33Z")
He had nothing to say until today. ---
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [June 4, 2016, 4:42pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/22 "2016-06-04T16:42:01Z")
I’ve always wondered how islands like Hawaii can have waterfalls. That seems like more freshwater than should be there, like you’d need it to be raining 24/7. Obviously I don’t understand it. ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [June 4, 2016, 5:10pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/23 "2016-06-04T17:10:39Z")
mks57: That’s desalination, not desalinization. Ranger Jeff: That’s a navy shower. Though not an island, Gibraltar is a “presque ile” (French for "almost island) which had acres of metal catchment areas when I climbed it in 1965 and '66 (courtesy of the USN). They now use desalination, 100%. Info on the methodology is germane to the OP: > **[Water supply and sanitation in Gibraltar](https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in_Gibraltar)** > > Water supply and sanitation in Gibraltar have been major concerns for its inhabitants throughout its history, from medieval times to the present day. The climate of Gibraltar is a mild Mediterranean one with warm dry summers and cool wet winters. Since daily records of rainfall began in 1790, annual rainfall has averaged a mean of 838 millimetres (33.0 in) with the highest volumes in December and the lowest in July. However, most of Gibraltar's small land area is occupied by the Rock of Gibral... ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [June 4, 2016, 5:14pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/24 "2016-06-04T17:14:19Z")
And here’s the dope on Hawaii. BTW, some of it gets 12 feet of rain or so per year, ergo waterfalls. [http://www.ctahr.hawaii.edu/oc/freepubs/pdf/rm-12.pdf](http://www.ctahr.hawaii.edu/oc/freepubs/pdf/rm-12.pdf) ---
**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:** [June 4, 2016, 5:25pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/25 "2016-06-04T17:25:26Z")
> [@levdrakon](#): > > I’ve always wondered how islands like Hawaii can have waterfalls. That seems like more freshwater than should be there, like you’d need it to be raining 24/7. Obviously I don’t understand it. The sun evaporates enormous amounts of water vapor off the surface of the sea in the tropics. It rains over the sea as well as over land. One thing that has a great effect on how much rain an island receives is its elevation. Mountainous islands intercept moist air and cool it off producing huge amounts of rain. Mountainous islands in the tropics are often covered in thick rain forest. On the other hand, the mountains can produce a severe rain shadow in their lee because there is no rain left to fall out once the winds cross the mountains. Hawaii has desertlike areas very close to extremely wet areas due to this effect. Low islands, in contrast, can be very dry because they don’t rise high enough to cool the air enough to condense the water vapor. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [June 4, 2016, 5:37pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/26 "2016-06-04T17:37:12Z")
> [@Ignatz](#): > > And here’s the dope on Hawaii. BTW, some of it gets 12 feet of rain or so per year, ergo waterfalls. In fact, [Mt. Wai’ale’ale](https://en.wikipedia.org/wiki/Mount_Waialeale) on Kaua’i is perhaps the wettest spot on Earth, getting an average of over 450 inches of rain per year. –Mark ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 4, 2016, 9:30pm UTC](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142/27 "2016-06-04T21:30:00Z")
Well, the martha’s vineyard info is now here … [Groundwater and Drinking Water | mvcommission.org](http://www.mvcommission.org/groundwater-and-drinking-water) Basically they don’t have dams, or flowing rivers… they only pump from wells … [Previous page](https://boards.straightdope.com/t/where-do-islands-get-their-water/315142.md?page=1)