Rainwater collection project

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  • Thu, Nov 05, 2015 - 11:14pm



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    Rainwater collection project

Adventures in Rainwater Collection

My good friend helped me build the first part of a rainwater collection system on the back side of our suburban home.  I have little-to-zero experience in construction so this was all an experiment.   We live in Virginia which averages 4″ of rain per month, frequently in brief torrential downpours.  About 800 square feet of roof will be the collection area.  How much water is that?  The general rule is that a 1″ rain on 1,000 square feet of roof surface area is 600 gallons of water.  For us, we might collect 800 to 1200 gallons in an hour.

We reviewed out water bill and found our monthly usage 1,000 – 4,000 gallons / month with the higher numbers in the summer due to garden watering.

There are 3 different standards for PVC pipe sitting next to each other at Lowes and they do not fit with each other!   I settled on Schedule 40 and returned all the “Sewer” (Drain Waste and Vent, aka, DWV) and “Schedule 80” stuff.

Basic design

1.  First flush diverters capture and hold the first 3 gallons of a storm’s rainfall which should include most of the dirt washed off the roof.  This first flush water is grimy dirty stuff that you don’t want in the storage tank.  The FFD was constructed from a 4” wide Schedule 40 PVC pipe with a “clean out tee” at the bottom.  When the Diverter fills to the top, a float rises to the narrow spot in the neck occluding it causing further incoming rainwater to overflow into the downspout for collection.

2.  Each down spout is a 3” wide PVC Pipe that descends through the deck into a “manifold” (a 4” wide pipe that collects water from all 3 down spouts) and carries it under the deck to the side of the house to the settling tank.


Future elements

3.  The manifold will rise several feet and dump into 2 separate 300 gallon IBC totes that sit side-by-side on a raised platform.  The raised platform is build with pressure treated lumber and serves to adjust the height of the tanks.  These Totes will function as settling tanks holding the rainwater for 24-48 hours, so that most sediment can settle to the bottom and not get transferred into the Green Storage Tank (GT).  The GT will be an absolute bear to clean—so I really don’t want to get much dirt in there.

4.   The totes will have 2 drains.  One is about 6” above the bottom and is used to transfer by gravity into the GT.  The lower drain is to discard the sediment ladened bottom layer.

5.   The 1,000 gallon Green Storage Tank will need to be situated on level packed ground.

6.   Our house sits on a gently sloping hill.  The garden is fortuitously down hill from the house and the tanks.  I should be able to gravity flow the water without pumps. (I hope.)

Can water flow uphill?   (Everyone asks me about this so I’ll mention it.)  Yes, it can in a closed pipe.  There is a device called a water level that uses this principle.

A water level


The system schematic

The FFD schematic.

And some pictures.

The first flush diverter is the larger structure that goes straight down from the opening in the eves.  The down spout is the smaller pipe coming off the top of the FFD.

A leaf catching wire mesh (not visible) covers the eves and another covers the opening of the down spout.

The clean out tee at the bottom of the FFD.

The float is put in the FFD.  This is borrowed from a toilet tank repair kit I got at Lowes.

The threads of the clean out cap don’t seal well unless wrapped with plumber’s tape.

The “manifold” is a 4″ PVC pipe that collects water from 3 down spouts.  It is hung beneath the deck with metal straps.

This is not my picture, but is “borrowed” from someone else for the purpose of showing an IBC Tote on a raised platform.  I am planning on using 2 of these 300 gallon IBC Totes as settling tanks.  They can be purchased on Craig’s List for about $100 plus delivery.  They are much easier to clean than the Big Green Storage Tank.

The Big Green Storage Tank.  The size of the tank was limited by 1) cost, 2) the width of the gate to the side yard, and 3) the weight that me and two friends could carry (and roll) up the hill to our house.  Hence, 1,000 gallons.

PVC pipe was cut using a standard miter saw.

When everything is put together and you KNOW that it fits perfectly, then you take one section apart, apply primer, then glue to it and promptly put it back together.  Once glued, it sets in about 5 – 10 second.  And you absolutely cannot get it apart after that.

My partner in crime:  Johnny Jackson.

This entire system is above ground and uninsulated.  We will have to leave it empty during the winter when freezing temperatures can burst pipes.

  • Sat, Nov 07, 2015 - 02:48am



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    You-go, Sand Puppy!

I have rain-water-collection-envy!!;)  Let us know how it works for you in the future!

  • Sun, Nov 08, 2015 - 08:41pm



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    this is great!

good job SP!

thanks for the detailed info and photos.

  • Sun, Nov 08, 2015 - 09:22pm



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    What are you going to do with the water?

Garden irrigation? Gray water system to flush your toilets? Filter it for drinking?

  • Mon, Nov 09, 2015 - 01:27am



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    Leaf Guards

Great Progress Sand-Puppy.

A couple of thoughts on the rain system……..If clogged gutters become a problem you can insert a leaf guard device between the gutter and the PVC downspout. It has a sloped screen that allows leaves to roll off and water to pass through. We install them on all new systems.

There is a ratio of first flush gallons to roof surface. It has evolved over the years, but at a minimum 2 gallons per 100 square feet of roof surface. The reasoning behind that has to do with toxic bird poo and other nasties. If the water is not for human use then it does not matter except that sludge and sediment will eventually accumulate in your tank if you don't adequately flush the system.

To treat the water for human use you can use a two step filter system. A 50/5 micron filter in a 20" big blue housing  followed by a charcoal filter in a second housing and then moving the water into a UV light to kill bacteria. Watts has a nice 12 gpm UV light at a reasonable price. 


  • Mon, Nov 09, 2015 - 01:41am



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I had one thought, SP, on your setup.

Since the FFD floats are not actually spheres, there's a chance they will float up with the cylindrical side 'up', and thus not seal. If trial proves this can happen, I'd try tying a small weight to the 'arm' end of the float- ensuring the hemispherical 'other' end is up.

For un-pressurized, "clean" work like this, I've heard of using silicone caulk instead of the cement, at least theoretically allowing for removing joints!

You may have planned this, & just didn't mention it: but I'd include a 'T' at the bottom of the inverted syphon, 'cause "stuff happens", and that would be even worse than the GT to clean out w/o it!

Otherwise, GOOD JOB and wish I had gutters to feed one like it!


  • Mon, Nov 09, 2015 - 07:53am



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    Thanks for your thoughts

OliveOilGuy, can you point out a specific product for filtration?  Are you meaning a filtration device like this one on amazon.com?   I would love to know more about how you got your awesome rainwater collection system set up to deliver clean drinking water to your house.

I put 2 wire screen guards on the gutters and didn't feel the need for a down spout screen.

But here is a low tech style wire screen downspout filter you could improvise.

And another more expensive one that could be purchased.

Sunguy–I really wish that I had though of silicon caulking instead of cement.  Great idea.  Not as irreversible as cement.

On the subject of weighting the bottom of the FFD float–I tried putting a bolt in the bottom to function as a weight, but got one that was too long to fit.  Maybe I'll head back to Lowes, yet again, and look for a more appropriate sized bolt that would function as a weight on the float.

Tom, Pinecarr and Reflector–thanks for the encouragement.  I am planning to use collected rain water to garden, but secretly want to be able to drink it in an emergency.  Eventually……  The system is being grown in stages with the next stage when time, money and good weather appear together.

I understand that a settling tank is one simple way to get lots of dirt out of the rain water.  So it functions like a filtration method.  That is my next step.

  • Mon, Nov 09, 2015 - 12:54pm



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    Filtration and Delivery System

You need to start with a pump. Davey makes some great pumps that don't require a pressure tank. Once the water is pressurized it goes to a filter like you showed from Amazon. Then a second filter of carbon, sand then finally through a UV light . 


  • Wed, Nov 11, 2015 - 11:33pm



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    Filtration and delivery information


Can you make any recommendations on books or websites to learn about purifying water from a rainwater collection system? I've got no experience with that sort of thing, and at this point in time I really don't have the resources to purchase a purifying system. I would like to have the information available to make a decision whenever I do have the resources. Could you please point me in the right direction on where to find more information. Thanks. 


  • Fri, Nov 13, 2015 - 06:32am



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Serious props man, good job!

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