# Rain water questions



## plantnoobdude (2 May 2022)

So, I have been using RO water for the past 1/2 year or so. but the waste is not really something I like.  now for the questions.

1. How much rainwater can I collect per week? the max I need is ~20l per week. 
2. how would one go about getting rainwater to collect, off the roof I presume?
3. how pure is rainwater? 
4. if collecting water off the roof, How do I know it is safe. (heavy metals and stuff?)
5. how large a water butt do I need?
thanks for reading.


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## seedoubleyou (2 May 2022)

plantnoobdude said:


> So, I have been using RO water for the past 1/2 year or so. but the waste is not really something I like.  now for the questions.
> 
> 1. How much rainwater can I collect per week? the max I need is ~20l per week.
> 2. how would one go about getting rainwater to collect, off the roof I presume?
> ...


There are ways of setting up RO systems for minimal waste. I’m sure a a quick Google search would bring something up.


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## tam (2 May 2022)

1. How much rainwater can I collect per week? Depends how big the roof you are collecting off, I can fill a 20l bucket in <20 minutes of heavy rain. There may be rain fall records for your area if you want to get technical
2. how would one go about getting rainwater to collect, off the roof I presume? yes, any roof, house, shed, greenhouse etc. divert the downpipe into a water butt - you can get a connector to do this
3. how pure is rainwater? depends on your roof, area, when the last rain fall etc.
4. if collecting water off the roof, How do I know it is safe. (heavy metals and stuff?) - you could test TDS and/or run it through a polyfilter, some people have daphnia in the butt as an indicator of quality
5. how large a water butt do I need? depends how much rain you want to store, in summer you can go weeks without rain so you want a big enough water butt to store more than a weeks worth, I'd just go for the biggest you can comfortably fit


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## seedoubleyou (2 May 2022)

If the waste is a real concern why not go 50/50 RO and the waste water?


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## plantnoobdude (2 May 2022)

tam said:


> 1. How much rainwater can I collect per week? Depends how big the roof you are collecting off, I can fill a 20l bucket in <20 minutes of heavy rain. There may be rain fall records for your area if you want to get technical
> 2. how would one go about getting rainwater to collect, off the roof I presume? yes, any roof, house, shed, greenhouse etc. divert the downpipe into a water butt - you can get a connector to do this
> 3. how pure is rainwater? depends on your roof, area, when the last rain fall etc.
> 4. if collecting water off the roof, How do I know it is safe. (heavy metals and stuff?) - you could test TDS and/or run it through a polyfilter, some people have daphnia in the butt as an indicator of quality
> 5. how large a water butt do I need? depends how much rain you want to store, in summer you can go weeks without rain so you want a big enough water butt to store more than a weeks worth, I'd just go for the biggest you can comfortably fit


Thank you! very helpful,
I'm thinking about maybe a 100-200l water butt as that should fit nicely where I plan on putting it. 
I will get some daphnia, it was mentioned on a previous thread by @dw1305 
I'm curious, how much TDS does your rainwater have?
do you know what the main contaminants of rain water are? 


seedoubleyou said:


> If the waste is a real concern why not go 50/50 RO and the waste water?


I don't want my horrible tap water anywhere near my tank. it is a softwater tank. my tap has over 20gh, 15kh.. horrendous.
If I can get rainwater to work, and still grow my softwater plants, that'll be great.


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## PARAGUAY (2 May 2022)

Presuming you have a back garden you could collect with several water butts greenhouse,garden shed house gutter eg.downspouts. Maybe for the amount you need if you have it left in a couple of buckets overnight ?Smaller the building easier keep roof clean


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## tigertim (2 May 2022)

My rainwater in East Yorks comes out at 1kh  5gh  7.5 ph, once the butts set up, it works out cheaper and easier to manage than a RO system, but as said make sure it will last a month without rain.


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## plantnoobdude (2 May 2022)

tigertim said:


> My rainwater in East Yorks comes out at 1kh 5gh 7.5 ph, once the butts set up, it works out cheaper and easier to manage than a RO system, but as said make sure it will last a month without rain.


Oh, I thought It would be lower to be honest. I'm not sure I want to use rain water anymore then. it should rain soon in london. so ill collect some rain from the roof in a bucket and test the tds. see where it is.


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## dw1305 (2 May 2022)

Hi all, 


plantnoobdude said:


> Oh, I thought It would be lower to be honest.


It depends where you live. If you live in one of the limestone areas (mainly S. and E. of England) rainwater picks up limy dust on its way through  the atmosphere and off of the collecting surface etc.  You only need a trace of CaCO3 to raise the pH, so I tend to ignore pH as a measurement (in all low conductivity water).

If you live near the coast you will also get sodium chloride (NaCl) in your water (from sea spray), it won't change pH ((NaCl) is a neutral salt) but it will raise conductivity. I've seen this effect (in Bath) so I would guess it probably effects a lot of the UK. Having said that it is a minor effect and our varies from a bout 30 microS in the winter to 120 microS in the summer after they've cut the corn etc.


plantnoobdude said:


> 3. how pure is rainwater?
> 4. if collecting water off the roof, How do I know it is safe. (heavy metals and stuff?)


Pretty pure, I use the <"_Daphnia _bioassay">, but this will only work if you have a bit of carbonate buffering in your rainwater.  I've <"used rain-water"> since the 1970s and I've <"never had any issue with it">. 


plantnoobdude said:


> 5. how large a water butt do I need?


The bigger the better, you need at least 200 litres storage and ideally twice that. I have <"three butts at the rear of the house"> and two at the front, although I also use them for watering the Blueberries etc.






cheers Darrel.


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## plantnoobdude (2 May 2022)

dw1305 said:


> It depends where you live


I live in London. not central london.
so, I take it the water should be fairly pure?

I will get some daphnia to try.


dw1305 said:


> The bigger the better, you need at least 200 litres storage and ideally twice that. I have <"three butts at the rear of the house"> and two at the front, although I also use them for watering the Blueberries etc.


alright, thanks!
ps. Your garden looks great!


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## dw1305 (2 May 2022)

Hi all, 


plantnoobdude said:


> so, I take it the water should be fairly pure?


Cities are probably safer than the countryside, where you have more of a risk from Agricultural pesticides. 

cheers Darrel


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## MichaelJ (2 May 2022)

plantnoobdude said:


> Oh, I thought It would be lower to be honest. I'm not sure I want to use rain water anymore then. it should rain soon in london. so ill collect some rain from the roof in a bucket and test the tds. see where it is.


I only tried to collect some as couple of times as an experiment - the TDS came out at around 20-40 ppm. (40-80 uS/cm).  I believe the   KH was <1 and GH ~2.  I have no idea how much it would vary over the season though.  If I could collect it consistently I would. It would only be practical for me in the late spring, summer and early fall however.  I use about 100-120 L of RODI water weekly for my two 150L tanks. A lot of waste water unfortunately 

Perhaps there is a middle ground there where you could collect _some_ rain water and mix it with RO water and perhaps a little bit of tap water.  The consistency  in terms of water parameters is what would worry me the most.  

Cheers,
Michael


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## MichaelJ (2 May 2022)

seedoubleyou said:


> There are ways of setting up RO systems for minimal waste.


Please share?

Cheers,
Michael


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## shangman (2 May 2022)

I get London rainwater, it's pH 6.6, kh0 gh2-4 when I last checked, which tbh was ages ago.

20l weekly is fine with one good sized waterbutt I've found. Ideally you need to wait a few months for it to fill up first. The only annoying thing about all this stuff is that it depends on the weather, sometimes there is rain and sometimes not. It's rare that I've been without, but I have access to 4 waterbutts and am very spoilt. There might be contaminents in it but I've decided life's too short and I can't be bothered to care about them, haven't noticed any problems. All my waterbutts have daphnia in it so I think that's a good sign.


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## Majsa (2 May 2022)

I agree with “the bigger the better”, I have a 100l butt for ~20l a week for my tanks and orchids and I occasionally run out of rain water (although storing water in jerrycans help). I’d like to daisy chain another 100l to it but need to convince the other half first


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## seedoubleyou (2 May 2022)

MichaelJ said:


> Please share?
> 
> Cheers,
> Michael


I’m unfortunately not we’ll versed in that area. I used RO when I kept a reef tank but the waste didn’t bother me enough when only filling up 25L.
I have a friend who has an RO setup with very minimal waste. 
Naturally if I had the answer I’d supply it, hence suggesting Google.
Sorry I can’t help.


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## seedoubleyou (2 May 2022)

This might help?
I know my mates is a 7 stage also.


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## MichaelJ (2 May 2022)

Hi @seedoubleyou   Thats pretty cool! I thought one way to achieve "zero" waste was to run the same water around or put it back in the heater or find some other use for it...  it's a very elaborate setup.  There are indeed some household RO systems that produces significantly less waste water. This one for instance:  Waterdrop G2P600 Reverse Osmosis Water Filtration System for Home

Cheers,
Michael


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## dw1305 (2 May 2022)

Hi all,


plantnoobdude said:


> ps. Your garden looks great!


I think that photo was taken in 2010, we got <"solar panels in 2011">, so it definitely predates that. 

This is  today (May 2nd 2022), so much the same, although I've had to replace one of the water butts (it started leaking in 2020).





cheers Darrel


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## Maf 2500 (2 May 2022)

I would think concrete/cement based roof tiles would add extra hardness to the collected water compared to a proper slate roof or a greenhouse roof. 

I tested my water with cheap test strips and the concrete roof appeared to read higher gh and kh than the greenhouse but accuracy is not all that with these types of tests (and I do not yet have a TDS meter).


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## Kelvin12 (2 May 2022)

Some time ago I was home brewing and collecting water from a tiled roof.   I was told by the "brewing experts "!!!! That silicone ? in the tiles effects the taste and I need to collect from an corrugated iron roof.   I couldn't taste any difference..    Obviously if there is silicone in the tile collected water it doesn't effect the fish.    

Dirk


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## ian_m (3 May 2022)

Kelvin12 said:


> That silicone ?


I assume you mean silicon. Silicon is an element, usually around us in the form silicon dioxide ie quartz and is practically insoluble in water at normal temperature and pressures. 

Silicone is an compound of silicon and organic molecules, used to seal sinks/baths and make rubber based compounds. Insoluble in water.


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## dw1305 (3 May 2022)

Hi all,


Maf 2500 said:


> I would think concrete/cement based roof tiles would add extra hardness to the collected water compared to a proper slate roof or a greenhouse roof.


It has some effect, but much less than you might imagine, mainly because the rain-water is only briefly in contact with the roof.

cheers Darrel


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## Maf 2500 (3 May 2022)

dw1305 said:


> Hi all,
> 
> It has some effect, but much less than you might imagine, mainly because the rain-water is only briefly in contact with the roof.
> 
> cheers Darrel


My roof is old (probably 1980's) and every time I clear the gutters of moss there are also significant quantities of course sand eroded from the roof tiles. The calcium carbonate has to be going somewhere and the runoff water seems the most likely candidate. Hopefully, as you suggest, the concentration is very low due to the large volumes of water over a year and the low contact times.


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## Aqua sobriquet (3 May 2022)

I’ve never tested the rainwater I use apart from TDS. It’s collected from the roof of a large shed with a rubber roof. I’ve been using it for a long time now and the Fish, Shrimps and plants don’t seem to mind it. TDS when I last checked was around 50. The water butt is 210L. I have two of these but the other collects from our  main roof which has what I think are clay tiles.


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## Aqua sobriquet (3 May 2022)

You can some fancy water butts these days.


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## dw1305 (3 May 2022)

Hi all, 


Maf 2500 said:


> My roof is old (probably 1980's) and every time I clear the gutters of moss there are also significant quantities of course sand eroded from the roof tiles.


That should be fine. If you were getting physical lumps of cement (or mortar) in the water butt they would have more effect (because of longer contact time). 

cheers Darrel


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## tam (3 May 2022)

Tested mine for you, the TDS was 48. Higher than I'd have guessed but I did just connect it and it's just got a downpipe straight off the main roof and has filled mostly from one down pour a month ago and a bit of drizzle so it's probably not very dilute. I think when I collected buckets mid pour it was closer to 30. I don't think the gh is very high though - haven't tested the rain, but I add about 40% hard tap and the tank is still only about 7gh so nothing near 5gh.


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## aquanoobie (4 May 2022)

plantnoobdude said:


> So, I have been using RO water for the past 1/2 year or so. but the waste is not really something I like.


Hi @plantnoobdude 
Well, not usual but very efficient can be adjusting RO waste flow. First you collect water from clean and also from waste outlets and calculate ratio. Healthy ratio clean to waste can be 1 : 4 or 1 : 5. I have had up to 1 : 10, for every litre of clean water 10 litre was waste. It was totally unnecessary. 

An easy remedy is to slap a valve on the waste water outlet and adjust it. It can be adjusted to your preferred ratio. Lesser waste makes the main RO membrane to end its life sooner but they are so cheap now it doesn't matter if it lasts a year less. I have had ROs running at 1 : 1 ratio at later stages, and new ones at 1 : 3 with no harm to their life span. 

What kills the main membrane prematurely is insufficient carbon cartridge leaking chlorine.


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## Courtneybst (4 May 2022)

I live in London also and use rainwater for various things but only recently for an aquarium. 

KH 3
GH 3
TDS 30~

I sometimes spot live food in there too. One thing I should note is that that water butt isn't from surface run off. It'll be interesting to see what the parameters might be with a downpipe fitted.


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## Ghettofarmulous (15 Aug 2022)

Older thread but I'm going to move to Rain water and do my bit. ill use the Daphnia Bioassay.  In addition, I have been feeding my house plants with rain water this past 6months and I noticed their health is better. No more crispy ends. I read that fluoride from tap water can lead to damaged leaves


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## Hanuman (15 Aug 2022)

Ghettofarmulous said:


> I read that fluoride from tap water can lead to damaged leaves


That and the chlorine. The carbonates in the tap water will also make it hard for the PH to decrease easily making some elements unavailable to the plants.


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