Wikipedia:Reference desk/Archives/Science/2017 April 14

= April 14 =

How do I know that the municipal water supply is safe?
I always boil water in a kettle, because that's what I've been taught. I think my parents have a habit of doing that, because they used to live in a developing country where parasites were a major concern, and the habit stuck. Also, somehow boiled water tastes better than unboiled tap water. But I've read that in a developed country, there may be toxins, like arsenic, in the water supply. Okay, fine. Am I doomed? Or maybe I am safe as long as my liver is functional? 50.4.236.254 (talk) 02:33, 14 April 2017 (UTC)


 * Doomed? No, not unless you've noticed that the rest of your town is suddenly really quiet.
 * But some municipal water supplies are not as clean as they're supposed to be. Flint Michigan was recently in the news for the Flint_water_crisis.
 * Where I used to live the water department was required to send everybody in town a letter every year to inform us that the levels of something or the other were very slightly higher than the legal limit.
 * As a point of interest, many beverages you buy at the store (Soda, bottled water, etc) are often made with tap water. Sometimes lightly filtered for taste, sometimes not. ApLundell (talk) 02:43, 14 April 2017 (UTC)
 * And where I live now, the town is required to test the water annually for about a hundred different things, and mail the results to everyone... not just if the results are abnormal, but normal as well. - Nunh-huh 05:15, 14 April 2017 (UTC)
 * I once did a lab in school about the water purity. Ultrapure water is used in extremely sensitive lab equipments, but the water is not drinkable. 50.4.236.254 (talk) 02:54, 14 April 2017 (UTC)
 * -- I personally drank ultrapure water twice (once because I was very thirsty and had nothing else to drink, once just for the hell of it), and while it tastes very flat, it's quite drinkable. 2601:646:8E01:7E0B:E123:F0BB:BC27:2FB0 (talk) 04:31, 14 April 2017 (UTC)
 * I agree with the citation needed. This guy also tried it [//www.youtube.com/watch?v=hMh1lyeNsPc]. Note that video presents the claim ultrapure water is dangerous because it's too pure and therefore risk significant mineral leaching from the body something quite a lot of sources seem to suggest, but I personally find it unlikely this will be a problem. I couldn't find a great source discussion the issue but if you focus on the people with some evidence they know what they're talking about, these discussions come to a similar conclusion. [//www.reddit.com/r/askscience/comments/18tg4q/hazards_of_drinking_upw_ultrapure_water_used_in/] (which links to  while dealing with deionised water which may have its own problems but it also dismisses the too pure claim.) This is only a risk if you're drinking quantities of water which are already getting up there in terms of danger. While these are mostly talking about general mineral content, I don't see a reason to assume the loss of minerals from any particular area would be sufficient to to be a concern. Storing the water in a container long term may however be risky depending on the container. (A copper one for example.) Nil Einne (talk) 11:24, 14 April 2017 (UTC)
 * Drinking ultrapure water can only leach minerals if that's the majority of what you drink, not just a one time thing. And only then if somehow you're happening to avoid deficiency based on the accidental concentration of a mineral in the drinking water that you aren't getting in food, which is extraordinarily unlikely.  That said, it's important to bear in mind that a typical ultrapure system is designed around being reliably ultrapure the vast majority of the time ... rather than being absolutely safe all of the time.  There's a risk that someone decided to clean and disinfect the system with something (I know they do that) and by mistake and bad luck now you're getting that in your water, for example. Wnt (talk) 19:32, 14 April 2017 (UTC)


 * You have to understand relative risks. The risk of bacteria or parasites in the water supply in a third world country is a serious one, as millions of people die each year from water-borne infectious disease.  The risk of arsenic and lead in the water supply in developed nations is extremely low, by comparison.  Even when contamination occurs, as in Flint, it's not at a level that's likely to kill anyone (they did have deadly Legionnaires' disease contamination, too, but boiling the water should handle that).  Also, water filters can remove many of those toxins, so, if you're concerned, you can use those. StuRat (talk) 03:29, 14 April 2017 (UTC)


 * In developed counties there are, at least, controls on what is allowed in the water piped into your home. In developing countries there may well be similar mineral toxins in water: it depends on the local geology, and the route the water has taken between falling as rain and ending up in your home. However, there will probably be no testing of the water. Boiling kills the bugs - but does nothing about the minerals. Most filters won't deal with anything in solution either. Wymspen (talk) 18:05, 14 April 2017 (UTC)
 * Well, I think my liver has the job of detoxifying the body of toxins. But if the toxins still manage to seep through, then I'd be doomed. 50.4.236.254 (talk) 15:12, 15 April 2017 (UTC)
 * If your liver fails, you're doomed no matter what you drink. Many of the toxins the liver handles are waste products of other bodily functions.  You can't avoid "toxins". You MAKE them. ApLundell (talk) 15:26, 15 April 2017 (UTC)
 * Fine. Whatever my body can handle is good. I'm still betting on a functional liver. 50.4.236.254 (talk) 16:48, 15 April 2017 (UTC)


 * Some other recommendations for safe tap water:


 * 1) Let the water run for a while before you drink it. You can use this water to wash dishes, fill watering cans, etc.  Most of the bad stuff in the pipes is washed out this way.


 * 2) Pour water into a covered glass container and put it in the fridge overnight, before drinking. This allows the chlorine compounds to outgas, and the fridge temp prevents things from growing in it after it loses the chlorine.


 * 3) Look at and smell the water before drinking. It may be cloudy at first, especially if there's an aerator on the faucet, but it should be clear and odor-free after step 2.  If it's a strange color, cloudy, or smells bad, don't drink it.  Note that while some things, like lead, can't be tasted, the same conditions which cause lead pipes to leach also tend to cause iron pipes to rust, and this rust you can see and taste. StuRat (talk) 16:57, 15 April 2017 (UTC)
 * I'm sure boiling water on the stove can allow the chlorine to outgas as well. Also, warm water can dissolve compounds better than cool water, so it is possible to dip some plant leaves or a lemon wedge in the water. Though, the ability of a compound to dissolve in water may depend on the compound's own chemical polarity. Oil is nonpolar. It does not mix with water. I think life's always a gamble. 50.4.236.254 (talk) 17:28, 15 April 2017 (UTC)

Summer ice in Hobart?
Hobart tells me that January's record low is a few degrees above zero. However, our article on the Tasman Bridge disaster (which occurred in early January) claims that several people died because they were in cars that "hurtled over the edge into the icy river", and this claim (complete with the ice) is in the cited source. Does Hobart really have river ice in summer, even though below-freezing temperatures have never been recorded in January? Hobart's latitude is similar to that of North American cities such as Boston, Niagara Falls, Toronto, and Milwaukee; we never hear of ice in those cities in early July. Nyttend (talk) 03:24, 14 April 2017 (UTC)


 * "Icy" can just mean cold. StuRat (talk) 03:31, 14 April 2017 (UTC)


 * I suspect it does mean that here, but to really know whether there could be ice on the river, you'd need to check the temperatures at its source (in the Central Highlands of Tasmania), not only at Hobart. --76.71.6.254 (talk) 06:43, 14 April 2017 (UTC)
 * No there would not be ice there in summer, and not even in winter. The water there is salt water. It would be well above zero, but feels cold if suddenly immersed. Graeme Bartlett (talk) 12:23, 14 April 2017 (UTC)


 * If the picture showing the gap was taken within a short time of the bridge collapse, it's evident there was no ice in the water. But as others have said here, it's entirely possible the water was much colder than the air, and calling it "icy" might be a bit of dramatic license on the part of the author. ←Baseball Bugs What's up, Doc? carrots→ 15:16, 14 April 2017 (UTC)


 * The author's point might be that the river is unexpectedly cold because like many rivers it flows from a higher altitude. However, I presently have no idea how much cooler the Central Highlands (Tasmania) would be than the vicinity of Hobart.  They say 700 m in River Derwent (Tasmania), which seems significant but well short of a typical snow line. Wnt (talk) 19:37, 14 April 2017 (UTC)


 * Actually, I just looked up and saw it can snow in the Central Highlands in summer (December and February) though apparently it is unexpected. The 700m figure for the river was misleading - the February story talked about elevations of 1100 m and above (the river per se is counted as being much lower than the highest peaks of the landscape).  So the water might not be much better than ice cold, depending on conditions that day...  That said, I just did a little sniffing around and found  to look up historical Australian weather data, which gives a table that in the days preceding this accident the minimum temperature at Hobart Airport was >10 C.   They also were high in late December 1974.  Of course, that's not the mountaintop, but in the extreme weather events Hobart and Launceton were also cold.  Wnt (talk) 21:44, 14 April 2017 (UTC)


 * Please note that the offending word, together with other hyperbole, has been removed from the article today. Alansplodge (talk) 21:34, 14 April 2017 (UTC)

At what point is something "wild" or "domesticated"?
If a tomato plant is found in a sewer, then is this wild or domesticated? What happens if plants on a farm (blackberries, for example) interbreed with wild blackberries to produce some kind of hybrid? Is the hybrid wild or domesticated? And what about a community who finds a wild avocado tree in the forest and decides to plant the pits and then select for the best ones? 50.4.236.254 (talk) 12:48, 14 April 2017 (UTC)
 * Domesticated usually implies that the organism concerned has not only been physically controlled (penned, fenced and confined, etc.) but has had its breeding controlled over enough generations that it has evolved, by artificial selection, inheritable physical differences from its "wild" ancestors. Animals (and plants) actually taken from the wild or with very recent wild ancestors are not domesticated, but tamed: they may (if animals) behave differently from wild exampes of their species (like not attacking people on sight) but retain a wild physiology. Individuals or populations of previously domesticated animals (and plants) may also revert to the wild, evolve in non-human-desired ways, and become feral. There will always be borderline examples where the appropriate definitions may be difficult to decide. {The poster formerly known as 87.81.230.195} 90.217.249.244 (talk) 14:18, 14 April 2017 (UTC)

Hydrogen vehicles
Hydrogen vehicle says the only exhaust product of hydrogen combustion is water vapour. Two questions:

(1) I am correct in assuming that the same is true of hydrogen fuel cells?

(2) Everything I've read about hydrogen cars implies or states that the water vapor emissions are benign. But do we know anything about the effects on local climate if, say, every car in a city is emitting water vapor in those quantities? Would the city's humidity be higher as a result? Would it get more rainfall? Anything else?

Thanks in advance. Loraof (talk) 16:53, 14 April 2017 (UTC)


 * 2) Note that gasoline engines also theoretically produce just about 100% water vapor, but the reality is that they never burn quite cleanly, so you do get other things mixed in (I also suspect some unburned hydrogen would be released from a hydrogen engine, along with oil vapor, etc.). Therefore, the effects of water vapor released by every car are already known.  It's not usually enough to affect the weather, but, in the right conditions (like a traffic jam with no wind and high relative humidity), it can create smog on the roads, which may impair visibility.  (If it was pure water vapor, then it would just be fog.)   StuRat (talk) 17:02, 14 April 2017 (UTC)


 * Okay, but isn't the amount of water vapor ejected per mile much higher for hydrogen vehicles than for gasoline vehicles, so the latter by itself would not give us a good idea of the effects, so the effects would have to be inferred based on meteorological models? Loraof (talk) 18:47, 14 April 2017 (UTC)


 * Think of how many gallons are in a gas tank. An equal weight of hydrogen would make a few times more water than that, but no more.  (2 H (MW 1) react with 1 O (MW 16), i.e. it produces 9x the weight of water as there was hydrogen)  I don't know how much hydrogen is in a hydrogen vehicle, but it is not more than a typical gas tank.   Well, you know how many gallons go out of lawn sprinklers on dry days - a lot more than that gas tank.  Also: Smog is not fog!  That said, I think it is theoretically possible for a bad hydrogen engine to release some hydrogen peroxide; this would release much less energy than water and isn't very stable, but it's conceivable.  Breathing enough hydrogen peroxide might be harmful, or it could abuse your hair - I can't imagine that really happening from a real engine but I don't know enough to prove it can't.  Wnt (talk) 19:06, 14 April 2017 (UTC)


 * I thought my 2 links to smog and fog made it quite clear they were not the same. Also, you need to account for the weight of oxygen pulled from the air in gasoline engines, to do a fair comparison. StuRat (talk) 21:06, 14 April 2017 (UTC)


 * I was comparing the weight of water produced to the weight of a typical gas tank (and actually, I omitted the low density). It is true that gasoline ~= -CH2-, so to one significant figure 1 C (12) + 2H (2) + 3O (48) -> CO2 (44) + H2O (18), which shows you get a bit more than 1 gas tank's weight of water out of a gasoline engine, plus a bit over three times its weight of carbon dioxide.  But that doesn't affect how much water is produced by the hydrogen engine, unless you want to subtract the tank's worth if it had been a gasoline car and make it a difference. Wnt (talk) 21:39, 14 April 2017 (UTC)
 * (Nitpick : The size of the tank is mostly irrelevant. People don't let tank size dictate their consumption. The exhaust-per-mile would be the relevant figure.) ApLundell (talk) 00:58, 15 April 2017 (UTC)
 * To answer part 1 of the question: Yes, a hydrogen fuel cell produces water. In fact, IIRC, proton exchange membrane fuel cells were used to provide both electricity and drinking water to astronauts in at least some Gemini missions. --Stephan Schulz (talk) 11:28, 15 April 2017 (UTC)


 * Almost all commercially available hydrogen is made from natural gas, so it is not carbon-free at the system level. A pure electric car's carbon use depends on where the electricity comes from. There are two types of hydrogen car: fuel cell and hydrogen IC. Hydrogen IC has some of the same problems as gasoline IC: (NOxemissions and inefficient while idling) while fuel cells act more like batteries, except for the H2O output. Gasoline, when used, creates water and carbon dioxide: 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O. It is unclear if the amount of water per joule is much less than for hydrogen. -Arch dude (talk) 03:33, 16 April 2017 (UTC)

Radio broadcast range and transmitter wattage
Please do not comment here There's a question at https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Miscellaneous#KCTV_.28Korean_Central_TV.29 that addresses the wattage of the transmitter and the range of transmission in terms of the invers square law. Comments regarding its accuracy would be helpful. Thanks. μηδείς (talk) 18:12, 14 April 2017 (UTC)
 * This has nothing to do with the question asked there. The question is: Why does the North Korean TV station KCTV only broadcast 8 hours a day? Akld guy (talk) 18:59, 14 April 2017 (UTC)
 * She wants a fact check of the claims made there, methinks. A fine use for the ref desk, IMO. Though the organizational aspects may be a bit debatable, one supposes the idea is to keep any criticisms or responses together with the original thread. SemanticMantis (talk) 19:29, 14 April 2017 (UTC)
 * The issue at Miscellaneous has been sidetracked into a discussion about radio wave propagation that has nothing to do with the question asked by the OP. Asking readers here to comment there is not going to help the OP. It would have been better to open a question about propagation here and ask readers there to comment here. Akld guy (talk) 20:04, 14 April 2017 (UTC)
 * You don't need to comment Akld if you don't think you can help, and I have already been pointed by someone who would not have answered had I not asked here to the proper answer. I had it right in the first place, and someone pointed out the proper article to show that.  I can't imagine what else one thinks the ref desks are for, other than getting the OP to the necessary article. This place is not a coliseum, but a collegium. μηδείς (talk) 23:44, 14 April 2017 (UTC)


 * Does that mean we are all κολέγιο τελειόφοιτος ? Was never any good at languages because it came across as all Greek to me ; ¬ }  Aspro (talk) 00:26, 15 April 2017 (UTC)


 * See the article Radio propagation. The Inverse-square law holds exactly for line-of-sight reception in free space. Since North Korea is not in free space, its radio and TV broadcasting is affected by the same phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering as that of every other country. Blooteuth (talk) 00:15, 15 April 2017 (UTC)

Another Australian weather thing
How were the New South Welshmen and the garrisons in Van Diemen's Land affected by the eruption of Mount Tambora? Since the first settlement of NSW occurred in 1770, presumably there's plenty of primary sourcing for 1810s events (diaries, church records, etc.), and History of Tasmania indicates that the first Tasmanians arrived a few years before the eruption, so I suppose that records might exist from this time period. And what about the Argentines and Chileans, the far southern Brazilians, and the Afrikaner settlements in the Cape Colony? Year Without a Summer, like everything else I ever remember reading, addresses the Northern Hemisphere, but I don't remember encountering anything about the volcano's effects on the Southern Hemisphere summers of 1815-1816 and 1816-1817. Nyttend (talk) 22:22, 14 April 2017 (UTC)
 * The first Tasmanians arrived some tens of thousands years before that eruption. --Shirt58 (talk) 03:06, 15 April 2017 (UTC)
 * At https://seasia.co/2017/04/08/a-blast-from-the-past-how-indonesian-volcano-changed-the-world there is a map showing the ash cloud (unreliable source) that only shows Western coast of Australia affected, so NSW and VDL are off the hook according to that. Graeme Bartlett (talk) 07:01, 15 April 2017 (UTC)
 * At https://www.mdba.gov.au/kid/files/2265-DroughtsInMDBsinceEuropeanSettlement1.pdf it claims weather on the east coast was wet and stormy due to Tambora. Graeme Bartlett (talk) 07:19, 15 April 2017 (UTC)