Is treatment required for harvested rainwater for toilet flushing?

  • Jennykay333
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Rainwater for toilet flushing

Hi everyone,

I'm sure this must have been discussed somewhere on this website but I can not find a thread on it, I'm looking for guidance on whether treatment is required for harvested rainwater for toilet flushing.

I guess the requirements vary round the world, but a starter guide would be helpful. If you know of existing threads on here or can give advice on this thread that would be great!

Thanks!

A civil engineer from UK currently working in Rwanda
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  • IlhaSolteira
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Re: Reply: Rainwater for toilet flushing

Hello Jennykay333

My name is Maurício A. Leite.
In Brazil we have few exemples with Rainwater for toilet flushing.
There is a NBR 15527:2007 Rainwater - Cachtment of roof in urban areas for non-potable purposes - Requirements.
Urfortunently is wrote in Portuguese.

Below there are 2 links:
conteudo.useaguadechuva.com/reaproveitam...e-chuva-residenciais
www.naturaltec.com.br/agua-de-chuvareuso/

I hope it can help you.

Best regards.
Maurício A. Leite
www.feis.unesp.br/#!/departamentos/fitos...ntes/mauricio-leite/
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  • erkkisantala
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Re: Reply: Rainwater for toilet flushing

Dear Jennykay333,

in addition what is mentioned in the answer from Brazil, you could possibly utilize a new European Standard EN 16941-1. It has been finished in 2018 and I think you could get hold of it through your own country´s standardization authorities/organization. It is not available free and for that reason I can not give any link to it. However, the price of the print or e-publication should be reasonable. It is written in English, German and French.

Greetings,
Erkki Santala
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  • erkkisantala
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Re: Reply: Rainwater for toilet flushing

Sorry,
I forgot to write the name of the standard. It is: On-site non-potable water systems - Part 1: Systems for the use of rainwater.
Erkki Santala
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  • muench
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Re: Reply: Rainwater for toilet flushing

Thanks for these really helpful links. In a nutshell, could you say what treatment is required? I would assume no treatment required for pure rainwater, but as the rainwater usually comes from roofs, you'll have to have sieves to keep out things like leaves and grit, right?

Also another thing to keep in mind is that the rainwater will be soft water (low concentrations of ions and in particular is low in ions of calcium and magnesium - en.wikipedia.org/wiki/Soft_water ). This is actually beneficial in terms of lower propensity for struvite formation in any pipes.

Anything else to keep in mind? Oh yes, and sufficient storage volume is required to make it through dryer periods.

In our street where we used to live in Germany, many of the newer houses had large cisterns below ground where they collected rainwater. This was used for toilet flushing, laundry and watering the gardens. These newer houses also tried to have zero run-off from the properties, i.e. when the cistern was full then any additional rainwater was meant to be infiltrated on the property. The aim was to have no rainwater go into the sewer which was a combined sewer in the area where we lived (common in Germany, if I recall correctly; i.e. no separate stormwater sewers in place, usually).

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  • Carol McCreary
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Re: Rainwater for toilet flushing

Hi JennyKay333,

It would be helpful to know where you're from and where you work. (This Forum is a safe space. Most regular users say a bit about themselves in their profiles. )

In 2017, the Water Research Foundation published the “Risk-Based Framework for the Development of Public Health Guidance for Decentralized Non-Potable Water Systems” and offers a number of free resources here. www.uswateralliance.org/initiatives/commission/resources .

Oregon-based Recode is doing serious work in the area of non-potable water reuse and offers model codes., policies, case studies and other guidance. www.recodenow.org/new-nexus-toolkit-by-resource-type/ See especially A Guidebook for Developing and Implementing Regulations for Onsite Non-potable Water Systems and the model program rules. Published in 2017 by the National Blue Ribbon Commission for Onsite Water Systems. uswateralliance.org/sites/uswaterallianc...WS%20REGULATIONS.pdf

Finally, here's a page PHLUSH website with material on traditional and green code and on ways to improve the current regulatory environment, especially in Washington State. www.phlush.org/ecological-sanitation/wa/

Please let us know if you find these resources helpful.

Carol

Carol McCreary
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Toilet availability is a human right and well-designed sanitation systems restore health to our cities, our waters and our soils.
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  • Decentral
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Re: Rainwater for toilet flushing

Dear All participants,

My comment is related to the documents as posted by Carol. The suggested train treatment is for black water and it is very complex and advanced. It is doubtful if it would be sustainable for the vast majority of cases. Unfortunately, there is no recommendation for treatment regarding storm/roof water, except requirements for bacteria. I would like to support Elizabeth's comments and may be to add, that a form of disinfection would be required. As this is a relatively new practice, there are no many regulatory documents to support it, as far as I know. May be I could suggest to add in the library a section as related to the use of roof storm water as an alternative source of water at on-site level, and to include there the European standards and other relevant documents or case studies.

Best regards,

Roumiana Hranova
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  • Jennykay333
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Re: Reply: Rainwater for toilet flushing

Thanks very much Erkki! That's useful to know, I will see if I can get hold of it. I didn't include in my post that I am working in Rwanda. I'm not always sure how strict the guidelines are to be followed in the EN standards, and I guess understanding what any risk is in not sticking to those guidelines.

A civil engineer from UK currently working in Rwanda
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  • Jennykay333
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Re: Rainwater for toilet flushing

Thanks Carol. I'm a civil engineer and working in Rwanda having moved over here in July from the UK. I'm working with a design firm who work on some different scale projects, for example renovating a school with pit latrines to a whole university campus which will have its own water and wastewater treatment works. And so not all projects meet guidelines from say the EU. What would be great to have is to know what level of provision is absolutely necessary and what the risks are of not providing this treatment. So in the case of rainwater harvesting, there are projects here that have implemented it for toilet flushing with no treatment except screening and I'd like to know the risks of not providing any other treatment and be able to make a better design decision.

Thank!

A civil engineer from UK currently working in Rwanda
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  • AjitSeshadri
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Re: Rainwater for toilet flushing

Dear Jennykay333
Rain water is fairly clean . Hence you provide screen filter of say 20 -30 mm holes at first.
Then have stone 100 - 150mm, pebbles of size 30-40 mm and gravel say 15mm aggregates.
This can be given in series.. each 1/3rd of a large chamber..
If you find water at outlet is muddy and coloured, then alum in a cloth bag is used in suspension .
If some sewage is mixed with rain water then use chlorine dosage.
You can adapt the arrangement as required on site condition.

With well wishes.
Prof Ajit Seshadri.
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  • Jennykay333
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Re: Rainwater for toilet flushing

Thanks Ajit. So it seems that disinfection is not always seen as a necessity. Or maybe this just depends on person to person as to whether they think it is required?

A civil engineer from UK currently working in Rwanda
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  • kurian
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Re: Reply: Rainwater for toilet flushing

Hello Jenny,
We have been extensively using harvested rainwater for drinking by adopting various technology options, which include roof top harvesting to recharge open dug wells, a major source of drinking water for Kerala State, India. Rainwater, if harvested scientifically following protocols is one of the purest form of drinking water.
Please see the link
www.ircwash.org/news/india-kerala-mazhap...amme-%E2%80%93-video

Also please see a manual attached

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