Does standing tap water really lose chlorine over time and become kind of better for watering plants?

[u/succulentandcacti]

Hi, did always read this recommendation to let tap water stand, so that hopefully if chlorinated, it'd degassify.

I know not all waters might be chlorinated with chlorine but rather with other compounds, but just wondering if there are some bases to have standing tap water become healthier for watering plants?

1. Increased CO2 dissolution, hence becoming slightly acidic?

2. Degassified or treatment chemicals breaking down due to air and sunshine?

3. Some other chemical breakdown, making it less sanitized (to the point that algae etc could grow if left long enough) hence less aggressive on roots?

Thanks for your help

[u/EricinLR]

It's my understanding this no longer works in most places in the USA, due to the switch from chlorine gas to the compound chloramine for water treatment. Chloramine is stable and does not offgas.

For horticulture, tap water is fine if your plants do not require ultrapure water. For carnivorous plants and some high altitude cloud forest orchid species, a reverse osmosis filter for your water supply is needed.

[u/Staggering_genius → u/EricinLR]

Even in systems that use chloramine, chlorine levels will drop over time. Source: my day job as water quality lead for a water utility.

[u/Marchtmdsmiling → u/Staggering_genius]

Lol everyone will just ignore us. Was going to chime in and say that chlorine levels, at least free chlorine (ie free radical) chlorine will drop as it reacts with things in the water. But it seems these people somehow want to believe that instead they need to be letting chlorine gas out into their home instead so chloramines won't come out as chlorine gas so they won't work.

Please people. Do you really think our tapwater is just a spewing source of chlorine gas, an absolutely horrible way to die?

Edit: those smells that you associate with chlorine, such as from a chlorinated pool, are really what are called trichlorethanes (wrong i meant trihalomethanes) and are what happens when chlorine reacts with organic matter.

Edit2: as was helpfully pointed out below, tce is not what I meant. I meant THM or trihalomethanes.

[u/apathetic_youth → u/Marchtmdsmiling]

I work in a friggin pool store and people don't believe that chlorine will disappear over time in pristine clear water, even if the water is in full sun. Chlorine, chloramines, however you put it in it just eventually goes "out". Ultraviolet light does not do either any favors.

[u/etcpt → u/Marchtmdsmiling]

You appear to be confusing trichloroethane with chloramines - the former is a sweet-smelling solvent while the latter are the "pool smell" chemicals.

You are definitely conflating ongoing reactions with DOM with offgassing. Depletion of free chlorine in chlorinated water on standing can occur through continuing reactions with DOM and other material, but it can also occur through offgassing. The speciation of chlorine in aqueous systems includes a small amount of Cl2 which is inherently in equilibrium with the gas phase over the water (Henry's Law) and, if the gas phase is regularly exchanged/if the chlorine diffuses out of the area, total chlorine can be reduced as the removal of one species pulls the equilibria to produce more of it in accordance with Le Chatelier's Principle. This has been shown experimentally in published work that also showed that boiling water further depletes measurable chlorine, unsurprising since the solubility of gases is inversely proportional to temperature. https://journals.bcit.ca/index.php/ehj/article/view/61

[u/Marchtmdsmiling → u/etcpt]

Ah no. It's been a while since college. What i meant was tri halo methanes. Tce was absolutely wrong. But so is thinking that you are smelling any of the ridiculously minor amount of chlorine gas that happens to off gas, depending on ph and temperature.

I am trying to educate people that the main way they will get water free of chlorine that forms the free radicals that are what make it toxic, is through these organic matter reactions. I forget the specific terminating reactions of chlorine, but in layman's terms chlorine will essentially continue to rip off electrons from everything and anything, until it hits those terminating reactions. They mostly involve organic molecules iirc.

If you have ever actually mixed bleach and ammonia, you will recognize that chlorine gas does not smell like we think of a chlorine smell. It smells like burning a burning feeling and acid coating your insides.

[u/mswfiber → u/Marchtmdsmiling]

Mixing bleach and ammonia, while not particularly safe, does not produce chlorine gas. It produces chloramines. If you're looking to produce chlorine gas, the easiest way to do that is to acidify household bleach with an acid it won't react with, like hydrochloric or sulfuric. Not a good idea but that's how you get chlorine gas

[u/SteveHamlin1 → u/Marchtmdsmiling]

If I vigorously spray tap water into a clean container, I can smell "chlorine". What is that?

[u/Marchtmdsmiling → u/SteveHamlin1]

Why do you think they put the chlorine into the water in the first place? To react with any dissolved organic matter and clean the water.

[u/Cold-Mango3542 → u/Marchtmdsmiling]

That's hard to believe because there's no organic matter in the pool and if there is organic matter in the pool everybody has to get out if you know what I mean

[u/69tank69 → u/Cold-Mango3542]

Organic matter is a lot more than just poop, it includes skin flakes, urine, bacteria, or even a leaf

[u/Raznill → u/69tank69]

Or a bug, or some pollen, or spores, unless this pool is in some form of a clean room there’s going to be organic matter in it.

[u/Marchtmdsmiling → u/Cold-Mango3542]

Ah so you don't sweat in your pool? Or leave any spit or snot? Or hair or dandruff. Unfortunately we are walking organic matter salt shakers just spraying it around us constantly

[u/atomfullerene → u/EricinLR]

>no longer works in most places in the USA, due to the switch from chlorine gas to the compound chloramine for water treatment.

The EPA says one in five people in the US are supplied with chloramine, so it's not most people by a long shot, but it is common enough that you need to check

https://www.epa.gov/dwreginfo/chloramines-drinking-water

[u/Rivereye → u/atomfullerene]

I'd be curious though how many in that group that doesn't receive chloramine in their water are on wells and not a municipal water supply.

[u/atomfullerene → u/Rivereye]

Only about 15% of the us is on well water, so the majority must be using municipal water

[u/salamander_salad → u/Rivereye]

Places with extraordinary water sources use simple carbon filtration. I’m talking reservoirs supplied by snow melt, artesian wells, or other sources of exceptionally clean water.

[u/hawaii_chiron → u/EricinLR]

It absolutely depends on where you live. Midwest and Rockies, for example, chloramine is sure to be used. But chloramine WILL degass, it takes about a week though. Just call your water utility, they can tell you quickly, which is being used.

Im lucky to live in a place with soft water, just chlorine here.

[u/MashedPaturtles → u/EricinLR]

Most places use chlorine, but a significant chunk do use chloramine, so you’d have to check with your utility.

[u/PM_ME_PHYS_PROBLEMS → u/MashedPaturtles]

And (I just checked my own utility and learned this) some places will use chloramine for most of the year, and switch to chlorine for part of the year.

[u/j0hnan0n → u/PM_ME_PHYS_PROBLEMS]

What are the criteria for the switch, I wonder?

[u/PM_ME_PHYS_PROBLEMS → u/j0hnan0n]

It is for general maintenance of the water systems (just googled it). Chlorine is more aggressive than chloramine, so the cycling is intended to clear out the biofilm that accumulates throughout the year.

[u/Kale → u/EricinLR]

I came to post this. You'll have to check your local water utility report or website. Places that use chlorine in the US, yes, letting it sit will off-gas the chlorine. If it's chloramine, though, it won't. You'll have to use fancier methods of purification to remove it.

[u/badgerj → u/Kale]

I believe you have to do the same for fish. Almost every region in N. America publishes local water quality data online, usually monthly/bi-monthly.

They should tell you if you’re on a chlorine/cloramine/ozone treated water.

Also any mineral content.

Heck my local water authority shows how much SARS-COV2/Influenza-a/influenza-b/RSV is in the WASTE WATER.

If not published on the web, you should be able to request a report from your local authority and perhaps they’ll charge you a small fee.

[u/atomfullerene → u/badgerj]

>Heck my local water authority shows how much SARS-COV2/Influenza-a/influenza-b/RSV is in the WASTE WATER.

Wastewater testing is actually a really good way to monitor how abundant certain diseases are in a city, since it's basically giving you a sample of the whole population. I

[u/Onigato → u/badgerj]

This is generally correct, YMMV on how responsive your local water authority is without FOIA-style filings.

For both fish and chlorine/chloramine sensitive plants (especially if you suspect chloramine) there are "dechlorinator" products sold under various different brands, usually for aquarium maintenance.

Most of them form a salt of chlorine (not usually sodium chloride, but metallic salts) which then precipitates out of solution.

[u/succulentandcacti → u/EricinLR]

What if Sodium Hypochlorite is used? Would that decompose by airing it?

[u/RainbowDarter → u/succulentandcacti]

If you're really interested in removing chlorine, you can use a carbon filter or add aquarium dechlorinator which is usually sodium thiosulfate.

[u/succulentandcacti → u/RainbowDarter]

Thank you. However this sodium thiosulfate would probably stay in the water, further increase the TDS, and usually plant roots don't like too much salts let alone sodium ions.

[u/VolsPE → u/succulentandcacti]

IDK too much about how plants favor K over Na, but I've always used potassium metabisulfate for chloramine removal. It's readily available from home brewing or wine making supply shops.

[u/ElSatchmo → u/succulentandcacti]

If they’re only using sodium hypochlorite, then yes it’ll air out or boil off fairly quickly. Bleach is just a combination of sodium hypochlorite and water. If they’re using chloramines then you can use an activated carbon filter, sodium thiosulfate, vitamin c, UV, or special brewers tablets, called campden tablets, to breakdown chloramines in the water.

[u/atomfullerene → u/succulentandcacti]

Yes. Fundamentally it's just another way to get the same end result as chlorine gas. When you add chlorine gas to water, it forms hypochlorite. Sodium hypochlorite is just another way to add the same substance.

[u/PotentialChoice → u/EricinLR]

Another alternative is rainwater. You can put a bucket under your downspout to collect it. Just don’t leave the uncovered bucket sitting out afterward, to avoid breeding mosquitos.

[u/EricinLR → u/PotentialChoice]

Not if you have a new roof. A rising number of shingles being sold for roofs in the USA are now coming with anti-moss coatings added to the surface. This runs off and is toxic to anything sensitive.

[u/crappy_ninja → u/EricinLR]

From what I understand chlorine is used as the primary disinfectant then ammonia is added, and the reaction creates chloramines. Which is the same reaction you get when you pee in a pool. And it's chloramines that give the strong chlorine aroma.

[u/spamjavelin → u/EricinLR]

For carnivorous plants and some high altitude cloud forest orchid species, a reverse osmosis filter for your water supply is needed.

And if you don't want to invest in an RO filter of your own, your local friendly aquatics store will likely have it for sale.

[u/suffaluffapussycat → u/EricinLR]

This is my understanding as well. You used to be able to leave tap water out overnight and the chlorine smell would be gone in the morning, but no more.

[u/Searching-man → u/EricinLR]

They make carbon filter cartridges (I've seen them for hoses) that should remove most of that too, instead of an RO setup. Unless you really need all the ions removed, RO should be overkill. I've never kept orchids or sensitive plants, but a carbon filter will take the chlorine/chloramine out. Brita filters (and other brands) usually have both a charcoal and ion filter, so those should work too.

[u/atomfullerene]

>Increased CO2 dissolution, hence becoming slightly acidic?

Possibly, although it depends on whether your water is buffered by dissolved minerals. At any rate, the water will come to equilibrium with local CO2 concentrations/pH in the soil pretty fast when you water the plant, so I don't think this will be too important.

>Some other chemical breakdown, making it less sanitized (to the point that algae etc could grow if left long enough) hence less aggressive on roots?

Besides chlorination, there's not really anything added to water to sanitize it. Municiple water systems might add fluoride to help protect teeth, and whatever mix of natural minerals are in the water supply will come along too, but none of that is likely to cause problems for plants and it also won't evaporate or break down in sunlight. Algae will grow as soon as you get rid of the chlorine (if you give it nutrients to grow on)

Broadly speaking I would say that there's not really much reason to let water stand out, other than to lose chlorine.

[u/etcpt → u/atomfullerene]

it depends on whether your water is buffered by dissolved minerals

It also depends on whether your water is already in equilibrium with the atmosphere when it is delivered to the tap. If your water is standing in a big water tower and equilibrating with the atmosphere, leaving it to stand under atmosphere in your home is unlikely to further increase the dissolved CO2.

[u/EricinLR → u/[deleted]]

Thank you! The OP's username suggests cactus/succulents, and those are far from needing ultrapure water in their environment. There is another source of this anxiety that's unspoken.

[u/codeprimate → u/[deleted]]

isnt the issue more about the impact of chlorine on symbiotic nitrogen fixing bacteria and fungal mycorrhizal networks?

[u/thebarkbarkwoof]

As just an observation,we have VERY chlorinated water. We have to run it through a Pur water filter just to be able to drink it. I have noticed that ice made with the water does not have the smell nor taste of chlorine even after it melts. I have been wondering the same thing, if it loses chlorine during the freezing process.

[u/mindjogger → u/thebarkbarkwoof]

does your ice maker have a filter?

[u/thebarkbarkwoof → u/mindjogger]

No. That's what confused me. I was thinking I should put filtered water in but it seems good.

[u/WiredSpike]

Cities use chloramine now and it won't evaporate.

For most plants, chlorine in the water is not a problem at all, and soil will neutralize most it.

You can add a tiny amount of vitamin c to the water and will instantly neutralize both chlorine and chloramine.

[u/dfinkelstein → u/WiredSpike]

THANK YOU!!

This is a huge help to me. I had no idea. I can put off my laborious plans of a water filtration system, now, and just skip right to buying sodium ascorbate and a big pitcher.

That's wildly helpful to me.

Thanks.

I'll make sure to only add right before use/drinking, and throw away after 24 hours since without chlorine/chloramine, and with now added ammonia as result of the neutralizing chemical reaction, the water will be prone to rapid bacterial growth even in the fridge.

[u/grafeisen203]

Yes, chlorine is volatile and evaporates into chlorine gas in an open container of chlorinated water at room temperature.

For the same reason, it's recommended to leave water standing for a short while before adding it to a fish tank.

[u/the_red_scimitar]

When I was a kid in the 60s/70s, I was an aquarium enthusiast. At that time, the common advice was to let tap water age uncovered for 24 hours, after which the chlorine levels would be low enough to not kill tropical fish. This did work. I think in the 80s that changed, in California, when they started to use Chloramine - a form of Chlorine that doesn't rapidly evaporate. There were always aquarium water de-chlorinators, but now they treat both forms of Chlorine, for immediate use with fish.

[u/diabolus_me_advocat]

I know not all waters might be chlorinated with chlorine but rather with other compounds

real good tap water (like what i have) is not treated chemically at all

i let it stand for a while (or simply take rainwater) so it may precipitate some of its hardness (which is not all too effective)

treatment chemicals breaking down due to air and sunshine?

yes, or simply reacting with organic matter - what it's treated for in the first place