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Rain water questions

plantnoobdude

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17 Mar 2021
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754
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uk
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. :)
 

seedoubleyou

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29 Mar 2022
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389
Location
Windsor
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. :)
There are ways of setting up RO systems for minimal waste. I’m sure a a quick Google search would bring something up.
 

tam

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5 May 2011
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1,230
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
 

plantnoobdude

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17 Mar 2021
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uk
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?
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.
 

PARAGUAY

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13 Nov 2013
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Lancashire
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
 

tigertim

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11 Jan 2015
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Hull
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.
 

plantnoobdude

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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.
 

dw1305

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7 Apr 2008
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nr Bath
Hi all,
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.
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">.
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.

back_wall-jpg-jpg.165483


cheers Darrel.
 

plantnoobdude

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MichaelJ

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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
 

shangman

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London
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.
 

Majsa

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26 Apr 2017
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The Netherlands
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 :)
 

seedoubleyou

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29 Mar 2022
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Windsor
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.
 

MichaelJ

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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
 

Maf 2500

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5 Jan 2021
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Slade Dingle
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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