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Rainwater Harvesting Experiences?


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Hi,

Is anyone doing rainwater harvesting and what has your experience been over a few years of using such a system? I'm interested in choosing one for a new build and using it in my toilets and washing machine (less so the garden).

I understand in the absence of water charges (Direct charges are currently suspended in ROI), there is no economic payback but I still feel it's the right thing to do.

I would be very interested in any good or bad experiences in having such a system in place and have you found it useful or not? Does it over complicate the plumbing, are there issues with the underground tank, smells from the water in the cistern/header tank etc.

Is it something you would do again and does it meet your expectations?

I think the benefits may be marginal at best (especially when occupancy is just 1 person!) but there may be angles I hadn't considered. Thanks!

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I've helped my off-grid friend in the next village with his system a few times.  After a lot of trial and error he's concluded that the best way to do it is to have an underground tank, so the water stays cool and dark.  This pretty much removed 90% of the problems he was having when he had above ground tanks. 

The other thing well worth doing is fitting a really good filter system on the collector, to keep out as much organic rubbish as possible, as that then removes the food for the bugs to grow on.

His system now works pretty well, but he can't use it for his washing machine now (he used to) as the newer machines don't run hot enough to kill the bugs in the rain water and the phosphates in the detergents provide loads of bug food.  What happened was that his washing machine got very smelly very quickly.

Rain water will contain a lot of faecal coliform bacteria, from all the bird poo washed off the roof, so you need a certain amount of caution as to how you use it.  Toilet flushing is fine, but I'd personally not want to use it untreated in a washing machine.  You could disinfect the water with a UV unit, but that's costly to run, as it has to be on 24/7, and would defeat any water cost saving.

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My plan is 4 IBCs for storage with a 5th that is the attenuation tank for the soak away at the end of the run. 

They can be plumbed together fairly easily and then I'm looking at some sort of non-return between the last one (holding tank) in the run and the rest so it's the only one topped up in the event that there isn't enough rain. I've also considered sticking a cheap ozone generator into the holding tank that runs periodically to kill off any nasties. Will have both a 5 micron and carbon filter on the pumped outlet to keep as much out of the system as possible. 

As Jeremy says, filtration is the key and keeping silt and rubbish out. Wickes sell a really neat drain outlet that will help but I will also look at filters that can be cleaned too. 

Ive added up its about £300 worth of bits, and water usage is around £90-110 when you include the cost of water and sewerage charges per year, so a 3 year payback. If I went for one of the commercial systems then it's a non starter as they are too expensive !! 

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I think I've said this before, but the chap in the next village uses linked IBCs and has just buried them.  He fitted standard small drain lids over the top of each one so he can get at the top cap and periodically clean them out if needed.  Since they've been buried they've not needed to be cleaned, whereas cleaning was needed regularly when they were mounted above ground.

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I researched this back in the early stages of our build as we were having the drainage put in.

In the end we ditched the idea of using the water for anything other than watering the garden and washing cars, patios etc for all the reasons above.

The commercial systems are ludicrously expensive. Instead we burried concrete chamber rings sat on a bed of waterproof cement and painted with tanking slurry. From memory they're 1500mm wide and stacked 3 high giving 1500mm depth. This gives us 2650 ltrs of storage which we felt was enough for what we needed. They have metal steps down to aid cleaning. Its sat between the source and soakaway.

Total cost was no more than a few hundred quid as it was all done at the same time as the drainage and soakaway.

As our build is massively delayed they've its been sat there for 2 years unused. But I check it every now and again and it works fine.

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23 minutes ago, Barney12 said:

[...]

The commercial systems are ludicrously expensive. Instead we burried concrete chamber rings sat on a bed of waterproof cement and painted with tanking slurry. From memory they're 1500mm wide and stacked 3 high giving 1500mm depth. This gives us 2650 ltrs of storage which we felt was enough for what we needed. They have metal steps down to aid cleaning. Its sat between the source and soakaway.

Total cost was no more than a few hundred quid as it was all done at the same time as the drainage and soakaway.

[...]

It's this kind of comment and feedback that keeps me coming back to buildhub over and over again. You've just saved me a good few hundred quid at least. Thank you.

Ian

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6 minutes ago, recoveringacademic said:

It's this kind of comment and feedback that keeps me coming back to buildhub over and over again. You've just saved me a good few hundred quid at least. Thank you.

Ian

Its also a rather useful air raid shelter so don't forget to fit an intake shut off :D

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With buried IBC's, would you need any sort of protecting wall or just literally bury them?

Also, what sort of micron would the rainwater need to be filtered to on the inlet?

Peter, you mentioned a 5 micron filter and a carbon filter, what are you intending to use the water for, gardens, washing cars, toilets?

Cheers

 

Vijay

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I'm planning a weak concrete mix as a footing followed by gravel and then topping off with concrete - they have a reinforced cage around them so as long as you are cautious to start with I don't think there are any issues.

You can't drive over them though unless you put a good 8-10" of concrete on them so I'm planning them under the patio with some well placed "removable" slabs to allow me to get to the caps when needed.

Only reason I'm using 5 micron and carbon is that its feeding toilets and the outside taps, and potentially the washing machine however as Jeremy says this can cause problems - that much filtration plus ozone potentially should sort out the nasties all being well !

Other choice is to chlorine shock the tank occasionally - not ideal but could be done.

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My previous late Victorian house had a rendered brick underground tank for holding rainwater. It was filtered through a sand filter and the water was always clear. Originally a lead pipe took the water into the kitchen and then the old copper.

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Gravity sand filters are really good for this sort of application, and I'm surprised they aren't used more often - yours is the first I've heard of in connection with rainwater harvesting.  There are several DIY designs for this type of filter on the web, mainly associated with cleaning drinking water in third world countries. 

Interesting that the Victorians used them in this application, although I guess it makes sense because quite a few Victorian water works used large gravity sand filters, before the advent of relatively cheap pumps and the switch to pressure filters (we have a pressure sand filter on our borehole supply).

There are lightweight filter media around now that are significantly better than sand, as they have a much greater surface area and being much lighter can be cleaned with a relatively low pressure backwash, whenever it's needed.

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The interesting thing about the filter bed was that it was two stage. It was a rendered brick box with a vertical slate separator with sand in each side. The inflow from the gutter downpipe flowed into the first side then over the slate, through the second, and into the tank. The tank was 4' diameter and 8' deep.

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That may have been an arrangement to deal with heavy rain, perhaps.  One problem with gravity sand filters is that they don't like high flow rates or turbulence, so perhaps the weir arrangement was there to calm the flow to the second stage?

I'm sure that the combination of a relatively small surge tank plus a modestly sized gravity sand filter, feeding a large underground storage tank would work very well indeed.  Using something like Turbidex (http://gapswater.co.uk/acatalog/Turbidex--1-cuft-5955.html#SID=251 ) instead of sand would give significantly better filtration from a filter, and be easier to backwash clean. 

I wonder why this sort of arrangement isn't used more often?  None of the commercial rain water harvesting systems I've seen seem to use something as simple and effective as this.

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31 minutes ago, Barney12 said:

I'm sorry to be thick.....

But how would you "backwash" a filter in this scenario? 

You'd close off the pipe from the filter to the tank, close off the buffer tank feed to the filter and allow the buffer tank to fill, have an overflow pipe from the top of the filter to take the muck and backwash water away then feed water from the buffer to the bottom of the filter bed, via a valve.

The backwash will lift the sand bed and fluidise it (a bit like quicksand) and will wash away all the lighter stuff that's been filtered out (which will be mainly organic solids and dead bacteria).  The backwash flows out the overflow and when the buffer tank is empty you reverse all the valve and put it back to normal service.  If the filter is big enough it probably doesn't need backwashing very often. 

Some big gravity sand filters are cleaned by just digging out the dirty sand every few years and replacing it with washed sand.  You could make up a unit that worked like that easily enough, and I suspect that's how the Victorian system Peter describes was periodically cleaned.

The sand will get clogged up eventually, and it depends how dirty the water is and how big the filter is, together with the volume of water that flows through it, as to how frequently that occurs.

 

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On 27/06/2016 at 08:31, JSHarris said:

[...]

but he can't use it for his washing machine now (he used to) as the newer machines don't run hot enough to kill the bugs in the rain water and the phosphates in the detergents provide loads of bug food.  What happened was that his washing machine got very smelly very quickly.

Rain water will contain a lot of faecal coliform bacteria, from all the bird poo washed off the roof, so you need a certain amount of caution as to how you use it.  Toilet flushing is fine, but I'd personally not want to use it untreated in a washing machine.  

[...]

We intend to have copper rainwater goods - so won't the resulting weak copper sulphate (? I'm no chemist) solution provide some anti-bacterial action while the water is 'resting' the tank? But will that - together with a simple but efficient sand filter - be enough?

And Debbie says the smelliness should be sorted by the weekly very hot (60)  wash. So that's Ok, then.:S 

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10 hours ago, Barney12 said:

But how would you "backwash" a filter in this scenario? 

Water enters the tank having passed through a filter first.  A pump lifts water from the saved rainwater and gets used in your house.

To make a backwash happen, arrange for that pump to also

  • Stop pumping to the house and instead
  • Pump water through the bottom of the filter up through the sand, direct to waste

If, while it's raining, you drop a spoon full of aluminium sulfate into the water somewhere upstream of  the filter, and wait for a while, the aluminium sulfate  (alum) forms a gel on top of the sand  and really cleans the water thoroughly. It helps greatly with the backwash process. A very small amount of alum will do the trick. I'm almost sure that alum has been used since Roman times to help purify water. Keep it away from your eyes.

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Personally I'd try and avoid the use of flocculants, like Aluminium Sulphate, both because of their toxicity and because they often only work over a limited water pH range.  Rain water is likely to be slightly acidic (it absorbs CO2 as it falls through the air and so contains a very low concentration of carbonic acid), but could be slightly alkali is you have a roof covering that tends to neutralise it.

Better by far to use a filter media that has a much greater ability to capture small particles, as that then avoids the need to use a flocculant in order to achieve good filtration.  The Turbidex I mentioned above will filter down to below 10µ, which is around three to four times smaller than a sand bed.

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I have rainwater harvesting for flushing WCs and garden watering/washing patio, paths and car.

no filters, underground tank, (very like a septic) pump to loft cistern, to WC cisterns.

perfect tiny ammount of fine silt in WC cisterns, nd more in loft store, lots in the underground one, I have trapped gullies on the rain pipes but some leaves do get in.

after two months of operation the water was smelly and I was advised to add a cup of cider vinegar it cured the problem.

 

i love using rain water for cleaning the windows.

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