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Above ground wet/charged system  RSS feed

Sarah Shaw
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Hi there, I've just discovered this forum and I can see I have a lot to learn - we purchased a 1/2 acre block 2 years ago and, having spent the last 2 years removing the last owners rubbish and blunders, we're finally getting our planting underway.  We have a large vegetable garden planned for the spring so I'm trying to get my water tank installed before then (its early winter here). 
I'm after some advice on my plans to connect my water tank.  I'm based in New Zealand so please forgive me if I use funny terms for some of the parts.

We have a 2nd hand steel tank with a capacity of 1800 litres.  I'm planning to connect it at one end of our rectangular house.  It will be used for the garden and, hopefully washing machine - so no need to be potable standard.

For neatness and to bring in the second downpipe from the other side of our deck I have planned to put in a wet system which will rise at the centre of the house wall and into the tank.  To one side of this junction will be a 100mm access point - a t-junction with a screw cap opening facing down - so that I can periodically drain the wet system and flush the pipes though, if necessary, to clear blockages.

The pipes that run from each down pipe to the tank inlet will be attached to the baseboards of the house - above ground.  This if for 2 reasons - 1 so that I can access the system for maintenance and 2 so I dont have to dig!

All pipes will be 80mm diameter except the access point which will be 100mm.

No first flush as I've read mixed reviews and will have the ability to manually flush the system and it is not for potable use.

I've attached a plan - not to scale!
Our rainfall intensity is 100mm/hr
The roof pitch is 11 degrees.

I'd be interested in what people (with more experience than me!) think of my plan and also if the 80mm pipes will be sufficient especially when the flow combines into one pipe to enter the tank.

I have used 80mm as they are coloured and dont come in larger sizes - so, if possible, I'd like it to match and look pretty!
[Thumbnail for downpipes.jpg]
Downpipe plan
Justyn Mavis
Posts: 26
Location: FEMA District III
chicken duck forest garden
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I have a few question for you.

1.) What are you using to catch the water from the roof?

2.) Are you adding filter system before it enters the tank?

3.) What is your plan for overfilling?

4.) Water volume by month/year?

I'm going to add a few tips.

1.) 3 inches pvc ( 80 mm)slip is over the edge of your roof line. then you can add fitting to it to direct it to the water capture areas.

2.) a 5 gal bucket (19L) drill holes in bottom, then add rocks, and screen door screen (mosquito netting) hold on with rubber band or rope. This goes onto your water capture area, the pipes leading from the roof go into this ( bucket rock filter) first then the water capture area.  This makes a very easy clean out. keeps bugs out of your capture area, and at a level of filtration. (Personally I drink the water straight from my water capture system)

3.) near bottom have a cleanout value, and near top have a place to install an overflow pipe so you can add another water capture unit.

4.) volume

Here is my example. I have a 30'x60' metal roof building I have around 50 inches of annual rainfall. I can capture 56,103 gal a year
162 m2 metal building x 1270 mm annual rain = 205,740 litres


I've build 5 unit. Most of this is 3rd world tech I've learnt in my travels.


Joe Wamsley
Posts: 11
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You might YouTube search for homesteadonomics. He is in the desert and gets his water from rain catchment. I think he is doing what you have described. He has pipes that go up to his gutters and are sealed so the water fills up the pipes and when the level gets high enough it dumps into his storage system. He is great about answering questions and just put out a new video on his raincatchment.
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