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Help me clearing the myth of chlorine in tap water and how bad it is?


Well-Known Member
It was my understanding that it is bad, in particular if you're growing "organically" to use fresh tap water that contains chlorine (or chloramine).

If you look around, you will come across countless posts where people recommend to keep water sitting out for 24hrs to let the chlorine evaporate.

The idea here is of course that the chlorine (or chloramine) is bad for the micro organisms in the soil.

Now I come across several interesting articles like

A Guide for Using Tap Water in Your Garden - The Grow Network : The Grow Network

where they BASICALLY say that chlorine, while possibly not "optimal", is not really harmful because IF AT ALL, it would only hurt micro organisms 1/2" down into the soil, there where (when you grow outdoors) micro organisms would be killed anyway by heat and sun.

I also read that the typical soil contains so many micro organisms which multiply so fast that cholorine in tap water is really a total non-issue. Tests have been made trying to kill the organisms but even with watering every day with lots of chlorine in the water, the micro organisms were thriving.

What I would like would be NOT just people commenting with the usual "hear say" and echoing what they read elsewhere, but actual EXPERIENCES of people who use (hard) tap water that has chlorine in it and whether it made any difference to have water sitting out, or just water straight from the tap.

** Related:

There are ways to dechlorinate tap water, some recommend H202 and others Vitamin C. One person mentioned a VERY TINY amount of 1-2 drops (!) H2O2 per gallon of water would be sufficient to get rid of all the chlorine.

My question here is...if the idea is to make the water "more suitable for micro organisms", then wouldn't the H202 do more harm than good...or is such a tiny amount like 2 drops of 3% H2O2 solution so little that it would indeed get rid of all the chlorine...but have no effect whatsoever on microorganisms?

--> in case you wonder why I even ask all this....in previous seasons I always kept buckets of water outside over night "to let the chlorine evaporate", but it sort-of becomes a pain in the ass, especially outdoors where it is MUCH easier to just take the hose when I want to water. I really wondering whether all this "let the chlorine evaporate" is just an urban myth and whether I would be as well off watering straight from the hose, ALSO when I want to grow organically.

** Related 2: When I take a bucket up on the balcony and fill it with the nozzle set to a fine mist/spray, you can literally smell the chlorine. Is it possible that filling a bucket that way would already get rid of lots of chlorine, seeing that chlorine is a gas?


New Member
If you grow in soil you can, absolutely and without any doubt, water your plants with straight tap water right away, without aerating it for a day or two. I speak from personal experience.

On the other hand, I've seen people watering their plants with water that has been sitting out for 24 hrs, thinking they have a chlorine-free water now, when in fact - they don't. They had their buckets sitting in shade.

In order to get rid of chlorine, water must be exposed to UV rays and that means direct sunlight. Otherwise, you might be as well watering straight from the tap.

BTW, chlorine and chloramine are two different things. The difference being that the latter you can't get rid of.

Bottom line - it's always a good habit to dechlorinate your water just for having a piece of mind but, nothing will happen if you use it straight from the tap.

Things in hydro are quite different but, even in that scenario, nothing's gonna happen if you top the res off straight from the tap every once in a while.


Well-Known Member
depends how your water. mine, is real good. a private company. ppm, is usually around 130. this, is most, if not all, calcium. the evidence of that, is on my water spiggot, on the fridge. lol. i allways fill my empty 5 gal buckets, and, i usually dont even need them, for a couple of days. i have used de-clorinator, with no bad results. use water straight out of my tap, with no noticable results. and, i allways use straight out of the tap, when flushing. in this way, i dont need to go thru a slow process, waiting. lol. all this organic this, organic that, etc, is a lot of hoopla, wasted time, effort, and money. there is nothing wrong with "non-organic" nutes. many, simply dont pay the "fee" to get the omri lable. and, the fda, got rid of all the bad stuff. unless you are putting bug killer on them. but, i am off subject now. everyone, has different water. some, is horrid! i cant beleive anyone would drink it. much of it, has a bad smell. like sulphur, or worse. i am blessed, to have the water i do.


New Member
i allways use straight out of the tap, when flushing.

IMO, flushing with pH'd water is also not necessary. The aim of flushing is, well, to free the plant of any excess nutrients and salts buildup. To do that, the plant doesn't care if the water is alkaline, acidic, or just in the Goldilocks zone. PH is important only for the nutrients absorption. When you flush it's like a torrent of water going through the cells, taking the abovementioned stuff with it.

Flushing with pH'd water makes sense only if you want your plant to absorb even the last traces of nutrients and micros she has left before chopping her off. This scenario applies only if you feed your plant moderately - and a lot of growers don't.

But if you pump up your plant full of nutes, especially towards the end of the grow - and a lot of growers do, then using the last traces of nutes is really of little or no importance whatsoever. She's already choking full of them - the main objective is to flush this crap out of her. And for that task, any water will suffice, pH'd or not.

As a matter of fact, in the last scenario, if you flush with pH'd water you might, actually, be doing more harm than good, by letting the already overfed plant absorb even more of the nutes. In that case, you're not really flushing her but pumping up more chemicals in her.

And that is the main reason people end up with smoke that is still harsh and chemical-flavored, even after a week or more of flushing and a month or so of curing.


New Member
More and more, municipalities are using choramine as a sanitizer.

Chloramine does not evaporate. The only way to remove it is to oxidize it or filter it out.

Complete waste of time letting water sit over night. This is why you have to shock a pool. To remove cholramine.

With water quality varying all over the world, I would not take rely on any experiences from others. Water hardness would probably be a bigger issue anyway.

The job of chlorine and chloramine is to kill bacteria. Use it at your own risk. I personally like my micro-herd too much to poison them.


New Member
If you grow in hydro, then yes. But there's no way chlorine can kill the bennies in soil. Absolutely no way. Water with that amount of chlorine would be harmful even to a human.

As for flushing, who cares? They're gonna be chopped in a week or so anyway. I say kill'em all :)

Chloramine is a different beast altogether. Chloramine is present only if ammonia is added to water, and not all municipalities are using it. As a matter of fact, chloramine is a weaker germicide than chlorine but it is its longevity that is pushing more and more people to use it. It is, simply, more stable.

You are right, however, about different water quality worldwide. One should not take for granted the advice of others but test his own water instead.

That being said, I do flush with pH'd water but only because I'm a light feeder and want all of the nutes absorbed by the plant and, simply, because there is no hassle associated with it. But, if I didn't have pH down, I wouldn't rush to my local growshop to buy it. I'd flush with tap water instead.


Well-Known Member
Yeah I know, in my hydro I use plain tap water and even use 3ml/L H2O2 because it stops algae from growing. The more sterile, the better.
But there is still the myth going around that tap water is "really bad" for "organic" and soil growing, but then there are those studies where they only found minor harm to the micro herd 1/2" down the soil since the chlorine can't even go further down, basically it doesn't harm the micro herd in any significant way.

For me this is significant since it makes a big difference needing to always have a bunch of buckets "ready" with water from the day before and lifting it up the stairs to water - if I just can water with the hose WITH NO PROBLEMS, like those articles say.

Yes I am also aware about chloramine, if this is the case the entire thing is moot anyway since you cannot get rid of it with "normal" simple things anyway. In my water quality report (in Spanish) I only see entries for "free residual chloride", which I understand is the leftover chlor(ine?)(amine?) at the tap after it is treated at the plant. And this report says this residual chlorine is below 1mg/L which would be astonishingly low anyway. (If I interpret this right).

And yes, hardness, pH etc. is another issue, but here my thoughts were just about the potential "risk" how the chlorine in tap water (allegedly) harms the micro herd if you grow "organically". And I don't want to do something unnecessary (leaving buckets out etc.) if there is no actual evidence that plain water kills the micro herd and is bad for organically growing. As it looks to me (for now), all this is anecdotal at best. (Also, from that line of thought, if tap water would be highly "disinfecting" and killing micro organisms in large masses, wouldn't it sure also be harmful to drink since it would kill beneficial bacteria in the gut etc.? Of course, no-one ever heard of such a thing. Just saying...)

"Water with that amount of chlorine would be harmful even to a human. "

Yes I just saw you came to the same conclusion....
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