Retro-fitting rainwater storage tank (garden only) - any thoughts?

[Weebles]

When we did the house drainage we had no money so we just drained our flat roof to a new soakaway. Now, we can afford a rainwater tank and with water bills going up and more dry spells and the garden still not finished we have an opportunity to fit an underground rainwater storage tank to serve the garden only.

 

Here’s what the drain looks like. There’s not enough space to fit a tank “in series” (ie before the circular catchpit) as we have a bit of a paved path in place now. But can we fit it “in parallel” ie spur off the pipe before the catchpit and then flow the overflow from the rainwater storage tank (sited to the left in the photo) back into that pipe before the catchpit? Is this a crazy thing to do? We would have to expose all this again too as it’s buried under an area  that is going to be turfed properly this year so this is the last chance. Was thinking a pump to a tap too. 
 

has anyone done anything like this?

 

[Nickfromwales]

Please browse the forum as this has been discussed quite comprehensively, with most in agreement that it costs more, long term, than it saves.  
 

 

 

[saveasteading]

13 minutes ago, Nickfromwales said:

most in agreement that it costs more, long term, than it saves.  
 

Yes, if it is only about money.

But it is 'a good thing' in reducing water consumption i summer and outfall to soakaway in winter.

You may have water for the garden when others have none, in a hosepipe ban.

In parallel could work if you get the levels right and the water to flow where you want.

Or change that chamber into a holding tank, with overflow going to the soakaway.

[Nickfromwales]

Hosepipe bans happen in extended periods of drought, so the water in there would be used quickly and not replenished.

And ironically, to keep the pump healthy, if you run short the tank will take perfectly good potable water from the cold mains to satisfy its thirst.

Cheaper to spray potable water on the ground is just the bones of it, unless you can bury 10,000L of storage or more.

Better off diverting rainwater to above ground IBC’s and using a £100 hippo pump until it fails and then replacing it when it does.

RWH pumps are stupidly expensive and fail as quickly as <2 years.

Buy solar PV instead.

 

Cant remember the last hosepipe ban either so I’ll not be investing 1000’s to protect myself……

[marshian]

39 minutes ago, Nickfromwales said:

Please browse the forum as this has been discussed quite comprehensively, with most in agreement that it costs more, long term, than it saves.  
 

 

 

correct me if I’m wrong but   @Weebles was talking about harvesting water for the garden - he wants to do what I should have done when I finished the extension at the rear of my house.

 

I was going to stick a couple of IBC’s under the ground and pipe them up - overflow goes to the soak-away but Mrs Alien wanted the garden back asap - so the soak-away got filled with rubble and covered up with brickweave

 

We now have 800 litres of water in water butts - we always run out of water in the summer so have to resort to mains water between them getting refilled with rain - no room for any more

 

It would avoid having to drain them down in the winter (water butts split when the contents freeze - unlikely to happen with underground storage

 

[Nickfromwales]

You still need to pump if underground, and there’s the cost of the kit and installation. RWH is RWH, regardless of what you do with the water?

 

Thats why I said do above ground and a cheap pump. 

[marshian]

1 hour ago, Nickfromwales said:

You still need to pump if underground, and there’s the cost of the kit and installation. RWH is RWH, regardless of what you do with the water?

 

Thats why I said do above ground and a cheap pump. 

You are still trying to overcomplicate it - Stand alone submersible pump dropped down a hatch above the tank - transfer to above ground water butt - fill the butt when you need too 

[JamesP]

As @marshian

If you have space, keep it above ground, fill from the gutters, have an overflow and pump. Don't spend 4K.

Keep it simple.

 

[marshian]

8 minutes ago, JamesP said:

As @marshian

If you have space, keep it above ground, fill from the gutters, have an overflow and pump. Don't spend 4K.

Keep it simple.

 

 

I'm not actually saying that............. It's what I have sure but if I had my time again it's not what I'd do

 

Brand new 1000 litre caged IBC £270 (+vat)

 

https://itppackaging.com/product/1000-litre-ibc-new?gad_source=1&gclid=Cj0KCQiAq-u9BhCjARIsANLj-s0zrUXn4IWfVXPObi3tiDAikpXTf-O-aLbMp_R8XvQKxOnCwDcmc_oaArjBEALw_wcB

 

You can get second hand ones for way cheaper than that but be careful what it was used to store there are a lot of really nasty chemicals that are shipped in IBC's - buying new means that's not an issue

 

My 400 Litre above ground rainwater tank cost nearly as much and they are a lot more money now!!!!

 

https://www.ebay.co.uk/itm/352521164934

 

Because it's above ground it goes green as hell and needs washing out every year

 

I need to

 

1. empty it before winter (all that rain wasted)

 

2. make sure I don't start filling it before March because of the risk of a cold snap - April showers don't always get me to capacity

 

3. transfer from butts that fill quickly to butts that don't to maximise storage capacity when it rains in summer (the biggest butt is on the smallest roof but Mrs Alien doesn't want a 400 L butt on the outdoor entertaining area so the largest roof area has just 200 Litres and I was lucky to get away with that.

 

None of those issues are a problem for below ground storage using cheap IBC's - you can't see it and if it's away from the house so no risk why spend a lot of money on fancy tanks and rainwater harvesting systems

 

I live in what is statistically the driest region of the UK - I have 800 litres of above ground rain water storage and it is not enough in summer for me to not end up using mains water (Mrs Alien likes her veg patch and fruit trees well watered)

[marshian]

On the reliability of a drop in submersible pump - parents previous three houses have been septic tank - "marshian senior" who is now 86 has watered the garden of all three houses for many years with the same submersible pump - mains powered - hanging on a rope - drop it into the water and amazing green grass all summer.

 

Current house is connected to main sewers and he's too tight to water the lawn with mains water and in the summer it's a shit show and it certainly isn't green.

[saveasteading]

3 hours ago, Nickfromwales said:

you run short the tank will take perfectly good potable water from the cold mains to satisfy its thirst.

That's for domestic  use, fully plumbed in to the house. Which I don't advocate.

I'm just suggesting that you might want to catch the rain for the garden.

Agreed re ibc tanks being far cheaper. I've done that for a new bus station, with 3 of them linked. With the tap slightly open in winter it also slowed flow to the sewers. But ugly.

[saveasteading]

10 minutes ago, marshian said:

800 litres of above ground rain water storage and it is not enough in summer

I have 3 small water butts. They run out for about 3 refills worth in SE summer. So it is simple and does fine as a pragmatic compromise. But I will put 3m3 underground as part of a new conversion  system, plus an ibc in a concealed area.

Better to design a garden to not need much water, and no buts about it.

 

[Alan Ambrose]

>>> But can we fit it “in parallel”

 

Looks like you have enough room to branch off at an angle and back again - it might depend on which tank though i.e. inlet and outlet positions and height. Min fall of pipe is, say, 1 in 100.

[Weebles]

Thanks all for the comments. Plenty to think about. Not least the cost - benefit debate.

[saveasteading]

1 hour ago, Weebles said:

the cost - benefit debate.

Building it inline as part of a new drainage system of course has benefits, as the work is small.

 

A new potable tank seems to cost £400  or so for 3m3. How much water cost would that save? 20m3 per annum x £2 x 10 years.....£400.

 

It doesn't need to be potable quality.

An old IBC will be £50 x 3..plus some pipes. But will that survive underground or does the plastic degrade? Plus it would need to have a cage to bear the ground load, and some cement board too. Any other suggestions?

 

[Temp]

We installed an underground tank and pump when we built our house. The instructions specified a concrete slab foundation to stop the tank floating out of the ground. It has a leaf trap/filter but has still accumulated a fine silt in the bottom. There is an access hatch/manhole cover to allow the pump to be lifted out. Gets used a lot in summer for garden watering. Can't remember the exact capacity but think it's around 2000L.

 

We also had a caged IBC on an allotment. This was raised up about 800mm on blocks laid horizontally so a watering can fits under the tap and gives a bit more pressure for a hose. I don't think the IBC we had would be cutting enough for underground use without more reinforcement. Probably need to fill it with water then concrete around it?

 

We nearly had a disaster with our turf. The weather changed to sunny and windy and we couldn't water it fast enough to stop it shrinking and gaps forming. We had two sprinklers going and moved them every hour but still wasn't enough. Couldn't use more sprinklers because the pressure dropped so the area being watered didn't increase. The rainwater tank ran out on second day. The next week or so we had the sprinklers on mains water.

 

 

Edited February 24 by Temp

[Nickfromwales]

18 hours ago, marshian said:

You are still trying to overcomplicate it - Stand alone submersible pump dropped down a hatch above the tank - transfer to above ground water butt - fill the butt when you need too 

Life’s too short for all that. Plus the storage of the butts / IBC isn’t something I’d ever want to see tbh. 
 

Tap > open

Hose > squirt, squirt

Beer > swig (beer purchased with the 4 figures saved) 

 

[marshian]

6 minutes ago, Nickfromwales said:

Life’s too short for all that. Plus the storage of the butts / IBC isn’t something I’d ever want to see tbh. 
 

Tap > open

Hose > squirt, squirt

Beer > swig (beer purchased with the 4 figures saved) 

 

 

I'm quite happy that you chose that direction

 

Every m3 I purchase costs me £2.10

 

The water cost isn't bad but it's the 90% sewerage charge that kicks £2.14 for every m3

 

So the saving is £4.24 for every 1000 litres of rainwater harvested for watering the garden (I also steal a bit for rinsing the cars after washing them because I hate the water marks you get with hard water - but don't tell Mrs Alien 😉 )

[saveasteading]

We will put in a tank between the house and soakaway, be part of the journey if you will.

I'm thinking 3m3. For the pump, I Can choose to immerse a battery pump with a hose or to a simple standpipe. Or a quaint village pump type thing.

Perhaps both.

It will be fed from 180m2 plan area of roof, so it will take 15 mm of rain to fill it.

July rainfall is 61mm. Maybe I should go 4m3.

 

I'll look on 'marketplace' for a tank. But for now, I'm going to think of whether ibc × 3 is sensible. At the right price, £25 yes. But people seem to want £50 or more. Then how to stop it caving in when empty?

It should never float because it will be full in wet weather. But a couple of spikes and a cable is simple.

 

All suggestions welcomed.

The BuildHub rwh for cheapskates/ the sustainably minded.

@Temp   @marshian

What would you do differently another time?

 

 

[Temp]

17 hours ago, saveasteading said:

What would you do differently another time?

 

Apart from the silt in the bottom the only issue we have had is with the tap freezing and bursting when we forget to wrap it up in winter, but this applies to all outside taps.  I should really build a permanently insulated box around it.

 

I forgot to mention we fitted a programmable timer to the pump so can set it up to water the garden while away on holiday but have never actually used it for that.

[marshian]

19 hours ago, saveasteading said:

The BuildHub rwh for cheapskates/ the sustainably minded.

 

@Temp   @marshian

What would you do differently another time?

 

If I had my time again I'd definately sink an IBC (or two) into the ground - with probably a small moss/leaf litter catch tank before them

 

If putting two I'd link them together so whilst the level might be lower in the summer the two would share the level

 

But as I'm not digging up my patio to do that now I'm thinking of an alternative plan when I re-do the 16 year old decking - I'm pretty sure I could get three low profile 400 litre tanks under the decking and collect the rain water there without it even being on show (I'd still have to drain in winter which would be a pain but manageable)

[saveasteading]

2 hours ago, marshian said:

putting two I'd link them together 

So would I. But perhaps the first one fills and overlows to the second. Thud the first tank is fuller and easier to pump.

And yes, a settlement tank before them. Divided by a porous manifold. maybe  a net.