# Rain Water Contents **URL:** \ **Category:** Factual Questions\ **Created:** [June 29, 2017, 5:25am UTC](https://boards.straightdope.com/t/rain-water-contents/790118 "2017-06-29T05:25:50Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [June 29, 2017, 5:25am UTC](https://boards.straightdope.com/t/rain-water-contents/790118/1 "2017-06-29T05:25:50Z")
What is in rain water, besides the water? Is it close to pure or does it contain a substantial amount of pollutants (especially in cities)? Just curious since it’s raining and I’m bored. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [June 29, 2017, 6:19am UTC](https://boards.straightdope.com/t/rain-water-contents/790118/2 "2017-06-29T06:19:02Z")
[Here is a nice pdf](http://www.people.carleton.edu/%7Ebhaileab/EnvironmentalGeology/RainWater.pdf) to get you started. It looks like rainwater is _a long way from_ being “pure”. It should be obvious, when you realize that clouds form when water vapor picks up dust and stuff in the atmosphere. Rainwater will _probably_ not kill you or make you sick, but in some areas it may well not be a good choice of beverage. ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [June 29, 2017, 11:11am UTC](https://boards.straightdope.com/t/rain-water-contents/790118/3 "2017-06-29T11:11:19Z")
It varies depending on what is in the air in which it forms and falls through. It will be naturally weakly acidic because of dissolved C02. But the number of other chemicals it picks up depends on where it falls. Where there are forest fires or industrial processes belching out smoke or volcanic areas can be a source of sulphur and increase the acidity of rain. There will also be a lot of lot of dust of various kinds from natural and manmade sources. If you google acid rain, you will find a lot of information, it makes grim reading. The stuff in rain shapes the landscape. Weakly acid rain gradually dissolves limestone and creates areas with a distinct karst topography riddled with caves. > **[Karst](https://en.wikipedia.org/wiki/Karst)** > > Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water, with few to no rivers or lakes. However, in regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimpo The stud... The dust from far off deserts travels on high altitude winds and falls with rain and you get a loess landscape. Takes a few million years. > **[Loess](https://en.wikipedia.org/wiki/Loess)** > > Loess (US: /ˈlɛs, ˈlʌs, ˈloʊ.əs/, UK: /ˈloʊ.əs, ˈlɜːs/; from German: Löss \[lœs\]) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. > Loess is a periglacial or aeolian (windborne) sediment, defined as an accumulation of 20% or less of clay and a balance of roughly equal parts sand and silt (with a typical grain size from 20 to 50 micrometers), often loosely cemented by calc... The air will be of different quality depending on the prevailing wind. If it is blowing over a city first, it will pick up a lot of pollutants and the rain will pick it up as it falls. Better to live up-wind where the air is fresher. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 29, 2017, 12:11pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/4 "2017-06-29T12:11:47Z")
Also, [bacteria](http://discovermagazine.com/2012/apr/07-does-rain-come-from-life-in-the-clouds). ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [June 29, 2017, 1:32pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/5 "2017-06-29T13:32:43Z")
From **eschereal’s** nice PDF: “We sent vials to relatives of our classmates and to Carleton College Geology Alumni, asking them to collect rainwater without contaminating the samples.” … I wonder, what would you have returned? … [chorkle] … Anyway … not sure the exact science … but water does like to condense/deposit **on** things … so called “nucleation” … be it dust, soot, smoke, bacteria, pollen, salt crystals, dead skin cells, etc etc etc … so each tiny cloud droplet forms up on one of these things, then combines with other cloud droplets to form rain drops, and the rain drop falls through the air column it picks up more and more … meh, downright dirty when it gets to the ground … yuck … Snow is even worster … double yuck … ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 29, 2017, 9:50pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/6 "2017-06-29T21:50:35Z")
> [@filmstar-en](#): > > The dust from far off deserts travels on high altitude winds and falls with rain and you get a loess landscape. Takes a few million years. It also makes your car dusty. Takes overnight. ---
**Author:** ![Salvor](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Salvor](https://boards.straightdope.com/u/Salvor)\ **Post date:** [June 29, 2017, 11:40pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/7 "2017-06-29T23:40:35Z")
In Los Angeles, I always assume light rain after long dry spells is the nastiest water on the earth, because all the filth and soot in the air is smashed into the falling drops of water before the drops hit the ground. After it has rained for a bit, then the water is more clean and pure, and for one brief moment, the skies of Los Angeles are pretty and clear. ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [June 29, 2017, 11:42pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/8 "2017-06-29T23:42:55Z")
Also, pro tip: Don’t drink the rain after a nuclear blast. ---
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [June 29, 2017, 11:49pm UTC](https://boards.straightdope.com/t/rain-water-contents/790118/9 "2017-06-29T23:49:27Z")
Thanks **Eschereal** for the PDF link, some good reading in there. I was wondering this due to the fact that whenever I use a hose or sprayer at a car wash, it always left spots on my car, no matter how fine a mist or how low the flow is. I noticed one day after a moderate rain, when it dried, I barely had any spots. Now I pretty much use the raining days to wash my car and just dry it when I get back and park in the garage (not to mention it saves time, except for the monthly polish). I never use soap on it and the towels always come out clean. I’m not planning on drinking rain water or anything, but glad to see its pretty safe. Thanks for all of the responses!