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I've seen a lot of information saying that chlorine can be bad for some plants and the suggestion to let the water sit out for several hours before using it on plants. I rarely see anything about chloramine, a common alternative to chlorine in municipal water.

Chloramine doesn't evaporate from the water (which is why it is used) but it has the same anti-bacterial effect.

Will chloramine harm plants the same way chlorine allegedly does?

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Here is an interesting site on chloramines, kinda makes me wish we were back to chlorine - a lot cheaper to filter. chloramine.org/chloraminefacts.htm –  user2283 May 23 '13 at 21:01

6 Answers 6

Short answer:

Chloramine water is about as safe for plants as chlorinated water is. Generally, as long as the plants/animals are not amphibious/aquatic (i.e., the water goes directly to the tissues), it should be fine to water your garden with chloramine water. In all other cases, the water will need further treatment before it can be used.

Long answer:

Chloramine is used these days instead of the traditional chlorine, because it stays longer in the water distribution system, thereby increasing its effectiveness. The most common sources of reliable information on the internet is from the US Environmental Protection Agency (EPA) and local public utilities' websites.

Some important points from the EPA's FAQs are (general):

  • Chloraminated water is safe to use for drinking and cooking.
  • Chlorine and monochloramine can be harmful to fish because they directly enter their bloodstream through the gills.
  • Chlorine and monochloramine can also prevent the growth of beneficial bacteria that are necessary for healthy fish tanks.

The last two points are also echoed in Stanford University Utility Division's infosheet (PDF):

Is chloraminated water safe for plants and animals that do not live in water, like my pet dog or cat?

Chloraminated water is as safe as chlorinated water for plants and animals that do not live in water. Chloramine is only dangerous for fish, reptiles, shellfish, and amphibians that take water directly into their bloodstream.

and also in the San Francisco public utilities commission's infosheet.

Scientific study:

The following study showed that root browning occurred in lettuce due to the reaction of hypochlorous acid in tap water and ammonia in the nutrient solution (the reaction produces chloramine).

S. Date, K. Naba, K. Kobayashi and T. Namiki, "Induction of Root Browning by Chloramine in Lactuca sativa L. Grown in Hydroponics", Journal of the Japanese Society for Horticultural Science Vol. 71 (2002) No. 4 P 485-489

The induction of RB occurred only when plants were cultured in the solutions containing both hypochlorous acid (HOCl) and ammonium ion (NH4+), but not in the solutions contained either HOCl or NH4+ alone. The addition of NaOCl (HOCl) followed by NH4H2PO4 (NH4+) solution after a 7-10 day storage or NH4H2PO4 followed by NaOCl solution induced no RB symptom. It was concluded that RB was induced by chloramine, a reaction product between HOCl and NH4+.

A followup study by the same authors is the following:

S. Date, S. Terabayashi, Y. Kobayashi and Y. Fujime, "Effects of chloramines concentration in nutrient solution and exposure time on plant growth in hydroponically cultured lettuce," Scientia Horticulturae, Volume 103, Issue 3, 30 January 2005, Pages 257-265, ISSN 0304-4238, DOI: 10.1016/j.scienta.2004.06.019.

In summary, it is highly possible that the anecdotal evidence in Susan's answer, re: burning of roots, and that of dying pond plants, frogs and fish is correct.

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I am a beekeeper and my bees have used tap water with chloramine for nearly a decade without apparent issues. That's been true for dozens of others who live by. I have not experienced, seen or heard of anything like your one anecdotal case. Do you have any actual research evidence about any of these things? I would love to hear it.

PS No rejection issues with my hummingbird feeders either, and my beer brews fine. It is not enough to start a group and spread scare anecdotes. If there are genuine, researched issues, I'd like to hear them, but scaremongering is just mean.

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Oh, by the way, chloramine can also be neutralized by boiling (30% gone with fast boil, 100% after 20 minutes) or by slight acidity (in soil, in your stomach, in small doses of vitamin C, or in coffee, tea, or even a pitcher with a slice of lemon added). But that's not necessary--it appears to be pretty benign, especially when compared to the waterborne diseases it prevents.) –  Jack Mingo Jul 3 '12 at 16:12
Was this intended to be a comment to the other answer? –  Joe Philllips Jul 3 '12 at 16:37
Yes. I am but a stranger here and I do not know your ways. –  Jack Mingo Jul 3 '12 at 16:45

Myself, I only have a casual interest in chemistry, but when you are also the son of a Ph.D inorganic chemist who spent his career on developing chemicals to clean things, you pick some things up.

Chloramine actually refers to a (very) large number of chemical compounds, the principal defining factor being a nitrogen-chloride bond somewhere in the structure. The simplest such compound is monochloramine (NH2Cl), an ammonia molecule with a hydrogen replaced by chlorine; it is generally seen in dilute aqueous solution, but in its pure form it is a gas at room temperature (25*C). So, distilling water by boiling at high temperature and feeding the vapor into an open-ended still will reduce monochloramine concentrations if present. However, monochloramine is used as a disinfectant because it will stay in water longer than "free chlorine" (chlorine from ionic compounds), and is less harmful to larger organisms (including plants). So, just putting a bucket of chloraminated water out in the sun will have a lesser effect than with chlorinated water (the free chlorine will exit the water at a greater rate than evaporation, while chloramines are much more content to sit in solution).

However, when you hear about "chloramines" outside of municipal chlorination, you are generally hearing about organic chloramines; these are compounds with an NHCl group or two, bound to one or more organic (H-O-C) molecules. These are by-products of disinfection by chlorine and/or quaternary ammonium compounds (quat sanitizers; based on ammonia, they'll pick up chlorine atoms easily); the chlorine (or chloramine) latches on to chunks of important enzymes or other key organic compounds in microbes, and the microbe dies due to the destruction, leaving the organic chloramine floating around (along with many more as the bacteria decomposes in the water). Organic chloramines are often aromatic; A pool that has the distinctive "chlorine smell" is actually one with a high concentration of organic chloramines that are evaporating. These are not incredibly stellar things to be drinking or to be feeding your plants, and don't disinfect well, although if your municipality has chlorinated water of any kind you will have SOME organic chloramines in it (except in the totally implausible case of there being nothing in the water to kill). Again, boiling water to distill it will reduce organic chloramine concentration, more so than with monochloramine alone.

Putting water out in the sun reduces overall chloramines indirectly, by consumption of monochloramine into organic chloramines; the sunlight and heat will cause the more aromatic of the organic chloramines to boil off. But, open standing water attracts more microbes, which the chlorine or chloramine kills and dissolves, then those organic chloramines boil off, more microbes come in, and the cycle repeats itself until there's no more chloramine in the water. But, by the time the chloramine runs out the water's pretty full of microbes, especially hardier ones that didn't get poisoned by the decreasing level of chloramine. So, don't drink water you've left sitting out, and be careful about eating things fresh from the garden when you've watered them with dechloraminated water. The microbes that were tough enough to survive the dechloramination process are not going to be things you want in your body.

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While this is a very detailed answer, it doesn't directly address the "harmful to plant life" part of the question. –  bstpierre Jul 6 '12 at 2:19

It would be helpful to understand that there is no such thing as harmful, harmless, safe, unsafe etc. Instead all things provide some benefit while causing some harm. What we really want to know is if the harm out ways the benefits or if the tradeoff cost of mitigating the harm is worth the effect and/or won't itself cause more harm than good. This applies to all technological decisions.

These are really questions about the scale of benefit to harm. It something that really needs to be expressed in numbers.

As noted above choloramines are a class of chemicals both natural and artificial instead of being just one substance. To evaluate the benefit to harm ratio, you first need to know which exact compound/s your local utility is using. Then you need to consider your plants and the soil.

Plants most susceptible to damage from anything in water are those who (1) grow in high water soils like marshes and/or (2) are heavily dependent on symbiotic fungus and bacteria.

Plants of type (1) have very little "skin" that keeps water from osmosing into and out of the plant. Such plants will readily absorb almost anything in water. For example, various marsh plants are used in the bio-remediation of soils with heavy metal contamination because the plants readily absorb the heavy metal salts in the soil and transport to their leaves on the surface. Desert plants by contrast have very think "skins" and won't soak up much else except nearly pure water.

Plants of type (2) usually also grow in moister soils although there is a lot of variation. In theory, the chloramines in the water could kill the symbiotic microbes and thereby damage the plant. On the other hand, it would also kill parasitic and/or disease microbes as well so the effect might be a wash.

I would say that if you have the time to remove the chloramines you might as well do so. However, if removing the chloramines means you might not water enough or might have to neglect other important care of the plants, I wouldn't bother unless you know for sure it necessary. Otherwise, you might do more harm than good.

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an informative answer that is much appreciated! Any references for your points? –  kevinsky Jul 11 '12 at 17:20

I am the Director of the Chloramine Information Center in PA. Chloramine cannot be evaporated or boiled out of water and is more persistent than chlorine. Therefore it maintains the chlorine around the roots longer than chlorine would. While we are not aware of any scientific studies on the effects of chloramine on plants, we have heard from a number of MJ growers, who are the best record keepers for plant growth, measuring yield, root and leaf health. They have recorded stunted growth, diminished yield, 'burning' of roots and browning of leaves.

We also know that outdoor pond plants have been killed off by chloraminiated water as well as frogs and fish. We also suspect that bees and birds are being effected. One bee keeper in PA lost 70 hives of bees overnight after his fall sugar feeding was made with chloraminated water. A neighbor also noted that the bees from other hives stopped landing on her backyard pond when the chloramine started. We have anecdotal information regarding humming bird feeders, where the birds stopped feeding when the water district switched to chloramine.

I hope this is helpful. If you have any other information that we can add to our library, please contact us.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

I wasn't expecting such a fantastic answer. Thanks! –  Joe Philllips Jun 5 '12 at 12:49
And they still put it in the water... –  corymathews Jun 5 '12 at 14:29
@corymathews the catch is that chlorine causes issues, and using nothing also causes issues. It's a juggling act to figure out the balance of it all. For plants, though, I'd suggest a rain barrel. –  DA. Jun 5 '12 at 16:56
Would you mind backing up the claims here? –  wax eagle Jun 13 '12 at 17:18
While I thought the Chloramine Information Center was a government agency, it's actually a "grassroots organization of over 2,000 citizens of Sourth [sic] Central Pennsylvania who oppose the introduction of CHLORAMINE into our drinnking [sic] water. Members of this group cross political, age and economical lines." (Copied from their website) –  shufler Jul 5 '12 at 20:02

From the perspective that healthy soil depends on lots of beneficial bacteria and other creatures in the soil food web, and that healthy plants depend on healthy soil, this quote above by yoda:

Chlorine and monochloramine can also prevent the growth of beneficial bacteria that are necessary for healthy fish tanks

would imply that both chlorine and chloramine can harm healthy soil, which is what we and other local Texas gardeners have experienced with chlorine.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

Hi, could you perhaps link to where'd the quote came from? –  wax eagle Aug 21 '13 at 13:45
quick google search offered many results, e.g. www.yamatogreen.com/beginners1.htm? Chlorine and chloramine pose other problems. These chemicals can harm fish, and can also damage the beneficial bacteria in your aquarium –  David B Oct 1 '13 at 21:31

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