Rainwater harvesting

[Jeremy Harris]

The easiest set up for toilets is to have a small rainwater tank in the loft (a tall cold water tank is ideal) and fit a float valve towards the top of the tank for the mains input and an inlet pipe to fill the tank from the rainwater supply pump.   Also fit a standard pump float switch, like this: https://www.whisperpumps.com/replacement-float-switch-for-submersible-pumps and wire that to a submersible pump that sits in the rainwater tank.

 

Set the mains water float to only operate when the level in the tank is low, by bending the arm down.  Set  the float switch to operate between the tank full level and just above the point where the mains water float valve opens.  Feed the toilets from this tank using gravity. 

 

What will happen is this.  You flush a toilet and it's cistern will fill from the loft tank.  As the level in the loft tank drops, the pump float switch comes on and water from the rainwater tank gets pumped up.  If the rainwater tank is empty, then the level in the loft tank will drop further until the mains water float valve opens and tops it up.  You need a pump that has dry running protection, and you may want to use a second float switch to turn the pump off if the level in the tank drops to the back up mains fed level.  A tall tank makes this system easier to set up, and avoid complex controls, yet remains compliant with the water regs.

[Pocster]

1 hour ago, JSHarris said:

The easiest set up for toilets is to have a small rainwater tank in the loft (a tall cold water tank is ideal) and fit a float valve towards the top of the tank for the mains input and an inlet pipe to fill the tank from the rainwater supply pump.   Also fit a standard pump float switch, like this: https://www.whisperpumps.com/replacement-float-switch-for-submersible-pumps and wire that to a submersible pump that sits in the rainwater tank.

 

Set the mains water float to only operate when the level in the tank is low, by bending the arm down.  Set  the float switch to operate between the tank full level and just above the point where the mains water float valve opens.  Feed the toilets from this tank using gravity. 

 

What will happen is this.  You flush a toilet and it's cistern will fill from the loft tank.  As the level in the loft tank drops, the pump float switch comes on and water from the rainwater tank gets pumped up.  If the rainwater tank is empty, then the level in the loft tank will drop further until the mains water float valve opens and tops it up.  You need a pump that has dry running protection, and you may want to use a second float switch to turn the pump off if the level in the tank drops to the back up mains fed level.  A tall tank makes this system easier to set up, and avoid complex controls, yet remains compliant with the water regs.

That sounds like an excellent solution !!

[Jeremy Harris]

3 minutes ago, pocster said:

That sounds like an excellent solution !!

 

 

A better arrangement might be to fit the float switch that turns the pump off when the rainwater tank is empty in the rainwater tank itself.  You can get three wire float switches, like this one: http://www.wiltec.de/float-switch-pump-level-controller-cable-5m.html?currency=GBP that can be wired to turn the pump power off when the rainwater tank is empty.

[Sue B]

Hi everyone

 

We are new to this but have a large kitchen garden to water during the summer months.  We therefore need a large water container or possible smaller connected ones.  We don’t particularly want a basement and the house is going to be about 50ft from the kitchen garden. I would want at least 10,000L for the watering.  Not looking at using any of the rainwater in the house (at the moment at least).  Have read the whole thread and realise I haven’t decided the language yet.  Any advice please?

[puntloos]

Dropping in since I've been mulling this over, JSHarris's post sounds exactly what i hoped would be possible - awesome =)

Except: is there a worry about Legionella? They start multiplying at 20C (although they typically are more of a problem at 40C), and if you're infested, flushing your toilet will aerosolize the legionella.. which is... less than ideal...

 

Assuming legionella can be headed off (filtering? chlorine? testing?), to buy:

 

- A loft tank

- A basement/groundfloor tank, embedded in concrete as discussed

- Collection and filtering (leaves?) off the roof

- Clever valve/float switch setup piping water to toilets and garden

 

How much would this be? Anyone tried it at this point, or done the math?

 

And would your normal plumber (during the housebuild) be able to rig this up properly or would you need either experts, or good DIY skills yourself?

 

-M

 

[Roundtuit]

3 hours ago, puntloos said:

 

How much would this be? Anyone tried it at this point, or done the math?

 

Materials aside, one day of your plumbers time will likely cover around 10,000 toilet flushes by my rough reckoning...

 

If you're looking at this as a cost saving measure, it needs to be done dead cheap I'd say, with a long term view.  If it's an environmental initiative, possibly better to buy your water, and in doing so, help finance large scale resource management by your supplier.  If it's to reduce reliance on utility suppliers, then it depends how much it's worth to you!

 

[Ferdinand]

Can I throw another alternative onto this thread? A large (perhaps also relatively deep for a high volume-surface area ratio) pond, and a pumped or gravity outlet.

 

If you have a SUDS Swale, it could even be a standing balance in that.

 

A pond could double as a reflecting pool, or even as a fire-brigade-lake if you are beyond the crucial 45m or significantly isolated.

 

I am not sure which regulations apply, but clearly Health and Safety for children etc.

 

Ferdinand

Edited May 8, 2019 by Ferdinand

[Onoff]

@Bitpipe, any updates on how your system is fairing in use? Guessing garden use and washing cars is it?

 

Interesting thoughts about bugs multiplying in there and aerosolizing in use from a wc flush, spray handset etc. Do you worry, guard against that?

[Jeremy Harris]

13 hours ago, puntloos said:

Dropping in since I've been mulling this over, JSHarris's post sounds exactly what i hoped would be possible - awesome ?

Except: is there a worry about Legionella? They start multiplying at 20C (although they typically are more of a problem at 40C), and if you're infested, flushing your toilet will aerosolize the legionella.. which is... less than ideal...

 

Assuming legionella can be headed off (filtering? chlorine? testing?), to buy:

 

- A loft tank

- A basement/groundfloor tank, embedded in concrete as discussed

- Collection and filtering (leaves?) off the roof

- Clever valve/float switch setup piping water to toilets and garden

 

How much would this be? Anyone tried it at this point, or done the math?

 

And would your normal plumber (during the housebuild) be able to rig this up properly or would you need either experts, or good DIY skills yourself?

 

-M

 

 

If the rainwater storage tank is below ground, then there's virtually no Legionella risk, as the water will sit at around ground temperature, which is usually around 8°C.  The loft tank is low volume, just a way to provide the required air break (assuming a two feed system, with the water for flushing being supplied by rainwater with mains water backup).  Because the loft tank is low volume, it will get emptied and refilled regularly, so there won't really be a body of water sitting up in the loft for long enough to allow Legionella to multiply.

[Vijay]

What loft tank size would you suggest?

[Jeremy Harris]

4 minutes ago, Vijay said:

What loft tank size would you suggest?

 

 

It needs to be big enough to allow for a toilet flush to not pull the level down too far, so that the rainwater pump float switch always operates before the mains water back up float valve. 

 

There also needs to be room for the float switch to control the rainwater pump, so that the tank is normally topped up to a level well above the mains water backup float valve trigger point.

 

At a guess I think that a 55 litre tank would be about right, as that would get flushed through pretty regularly and still have room for the float valve and float switch for the pump, bearing in mind that there needs to be an air gap so that the tank overflow is always below the mains water inlet point (can't remember the distance for this, but seem to remember that it has to be two pipe diameters clear).

[Vijay]

Food for thought, I was hoping to use a larger tank so the pump didn't run every time a toilet was flushed but wouldn't want to risk legionella 

[Bitpipe]

9 hours ago, Onoff said:

@Bitpipe, any updates on how your system is fairing in use? Guessing garden use and washing cars is it?

 

Interesting thoughts about bugs multiplying in there and aerosolizing in use from a wc flush, spray handset etc. Do you worry, guard against that?

 

I've not put a pump in yet so it's sitting in the dark being constantly replenished  Will be for garden only.

 

Not worried about bugs, it's quite cool down there and tanks are cool to the touch.

[Jeremy Harris]

20 minutes ago, Bitpipe said:

 

I've not put a pump in yet so it's sitting in the dark being constantly replenished  Will be for garden only.

 

Not worried about bugs, it's quite cool down there and tanks are cool to the touch.

 

 

There won't be a bug problem where your tank is at all, being cool and in the dark.  It's only really large loft storage tanks that present a significant risk, IMHO, as they may well sit for long periods at ideal temperatures for allowing Legionella to multiply (plus, probably, a host of other bacteria that get washed in with the rain water).

[Vijay]

Like bird poo that I think was mentioned before?

[puntloos]

Indeed I wouldn't overstate legionella either, it's just true that they are able to multiply in 20C. Perhaps a certain maintenance cycle (e.g. emptying the tank at least once every week, and leaving it dry for half a day) could work. But obviously it would require some type of bypass setup, unless you can hold it

 

But even that might just be overkill. I think indeed a smallish tank would suffice, having a single flush worth in the top tank. Yes you might have to use some tap water if there's two flushes needed..

 

@JSHarris: Do you have any idea of the additional cost of such a rainwater setup for say underground tank embedded in concrete, cleverly roof design to collect, top floor tank, 3 toilets and the garden hose over 'everything from mains'?

 

Edited May 8, 2019 by puntloos

[Jeremy Harris]

There's a long history of using large "cold" water tanks in lofts in UK housing, that suggests that Legionella isn't a significant problem with them, although the water from these cold tanks is only supposed to be used for feeding a hot water system, flushing toilets and supplying non-drinking water taps. 

 

The problem with the small tank is how to provide some sort of mains water back up, for times when the main rainwater tank runs low.  It's easy enough to do with an additional float valve and supply from the mains that has an air gap to comply with the WRAS regulations, but in practice it means sizing the loft tank so that the level can drop when filling s toilet cistern, but not by enough to trigger the tank to fill from mains water.  There are other control systems that could be used, perhaps having an electrically operated ball valve in the mains supply to a smaller tank, that's controlled by a float switch in the main underground rainwater tank, so that the mains water supply is shut off as long as there is enough stored rainwater.

 

The cost of rainwater tanks depends very much on how you choose to do it.  A fairly simple system, like that which @Bitpipe has installed, could be a couple of secondhand 1000 litre IBCs, placed in an outside basement area and fed from the roof downpipes, with an overflow system.  Coupled with a cheap submersible pump such a system would be fine for watering the garden, and could probably be installed for a few hundred pounds (I think IBC's are around £70 or so each, and a suitable pump for running a hosepipe might be as little as £100).

 

IBCs can't easily be directly buried in the ground though, so would need to be installed in an underground chamber of some sort.

[Bitpipe]

I looked at, but did not bother with rainwater for toilets as the additional plumbing complexity alone (separate cold feed circuit for every loo), plus the kit and provisions to meet water regs and run dry scenarios just did not make economic sense - was coming in at several thousand for a 3000l system I recall.

 

My IBCs cost £60 each and the other gubbins about £40. Will spend about £50 on a submersible pump when I get a chance - finally have power under the deck where the IBCs are.

 

Ok - I have a large concrete box but that was being constructed anyway as part of the basement additional means for escape and it was not that much more expensive to build a full depth box vs a half height.

 

Regards drainage plan, nothing special here apart from ensuring that all the roof drainage (front and back) collects to a single 110mm feed into your system and that you have an overflow to a soak away.

 

If you have ground level drainage (e.g. ACOs) these must drain separately to the soak away. No real extra cost doing this TBH, was just specified as part of the rain drainage system.

 

Essential that you have hedgehogs and good gully screens to prevent too much cr@p going into the system, but you'll still need a good filter and clean it regularly. 

[Onoff]

4 minutes ago, Bitpipe said:

I have a large concrete box but that was being constructed anyway

 

Daft question...couldn't you have just tanked the box and put a lid on it?

[Jeremy Harris]

10 minutes ago, Onoff said:

 

Daft question...couldn't you have just tanked the box and put a lid on it?

 

IIRC, from one quick look during a visit several years ago, the hole is the escape route from the basement, so had to be there and accessible via a door from the basement.

[Bitpipe]

13 minutes ago, JSHarris said:

 

IIRC, from one quick look during a visit several years ago, the hole is the escape route from the basement, so had to be there and accessible via a door from the basement.

 

Now has a deck built above it.

 

[Weebles]

We wanted to have a rainwater harvesting tank (garden and car washing only).  Have spent ages wondering if we can economically build our own as the kits are above £2.5K and I can buy alot of water (at current rates) for that money.  Have concluded that a water butt off the back of the house is going to be the most economical.  I think I can fit a pump to one of those to get the water to the veg patch in due course.  It won't be flash but honestly will do what want to - water some plants.

Those rainwater kits are ridiculously expensive.

[Bitpipe]

On 08/05/2019 at 15:53, Bitpipe said:

 

I've not put a pump in yet so it's sitting in the dark being constantly replenished  Will be for garden only.

 

Not worried about bugs, it's quite cool down there and tanks are cool to the touch.

 

I bought a 400w submersible pump from Amazon for £26 this week.

 

I had a 1.5" to hosepipe union so used that and tried it out today with the sprinkler - was not a success, water barely managed a few feet of clearance.

 

So just sent it back to Amazon and I've ordered a 1100W equivalent for £39.

 

Hoping that does a better job.

 

Oh - and sods law says that I got the order of the tanks the wrong way round as the one I was planning to use as my extract tank (nearest door) has a smaller cap so pump won't fit. No changing it now as there's a deck over the top!

Edited May 16, 2019 by Bitpipe

[Thorfun]

On 08/05/2019 at 18:43, Bitpipe said:

If you have ground level drainage (e.g. ACOs) these must drain separately to the soak away. No real extra cost doing this TBH, was just specified as part of the rain drainage system.

 

apologies for resurrecting this thread but @Bitpipe I've seen it mentioned a few times while investigating rain water harvesting that ACOs must drain separately to the soak away. can you please explain the reasoning behind this?

 

I ask because the Civil engineer designing our drainage has the ground floor ACO feeding in to the rain water harvesting tank but the basement ACO being pumped to the water course. before I go back and ask about this discrepancy I thought I'd ask what your reasoning was for the statement.

[PeterW]

18 minutes ago, Thorfun said:

 

apologies for resurrecting this thread but @Bitpipe I've seen it mentioned a few times while investigating rain water harvesting that ACOs must drain separately to the soak away. can you please explain the reasoning behind this?

 

I ask because the Civil engineer designing our drainage has the ground floor ACO feeding in to the rain water harvesting tank but the basement ACO being pumped to the water course. before I go back and ask about this discrepancy I thought I'd ask what your reasoning was for the statement.

 

ACO or linear drains at ground level - especially where vehicles are present such as driveways and garages - can introduce hydrocarbon contamination into the rainwater tanks