I install a 1200 gallon (4550 litre) rainwater harvesting tank to collect water for our garden when our irrigation well runs low in the summer. This is four part mini-series.
Install a Rainwater Harvesting Tank – PART 3: tank pump irrigation
Table of Contents
(this is a transcript from the video)
Even after we had 5 feet of mud removed from our shallow irrigation well, it still runs dry in the middle of summer. It’s definitely better than it was, but to expand our garden we need more water.
In this part of the series I’ll build a cedar and corrugated metal fence around the tank. So there’s the bare concrete curb filled with pea gravel.
The fence surround is constructed from 4x4 posts that are attached to galvanized post saddles. (I embedded anchor bolts in the concrete for these saddles.) There are 5 posts in total.
Between the posts I have a bottom rail made from a 2x6 then a mid rail and top rail made from a 2x4.
When we poured the concrete curb I embedded some anchor bolts to hold these adjustable post saddles.
I like these as they lift the post off the concrete by an inch.
And they are slightly adjustable. I find that my anchor bolt placement can be off a bit so this really helps.
After the design is done in Sketchup I can start cutting the parts. I have some cedar milled from trees that we fell on our property. These have been air drying for a few years. I had them milled full dimension and I really like the rough sawn look.
With a square curb I was able to design all the individual parts to be the same size. All the posts are the same length as well as all the rails are the same length. And this made cutting everything straightforward and pretty simple.
I cut all the 4 by 4 posts first.
The post saddles are designed for a nominal 4 x 4 which is actually 3.5 inches square. So I need to trim down the bottoms of the posts.
And I’ll break these wafer pieces off and finish with a chisel.
Next I’ll cut the 2x6’s for the bottom rails. And then the 2x4’s for the mid and top rails.
To flush mount the galvanized corrugated panels I cut a rabbet in the top and bottom rails. And I can use my portable table saw for this.
With all the parts cut I roll on a coat of stain. This is a one coat Sikkens semi-transparent stain.
The colour is called butternut. I used this same stain on the Garden Pavilion a built a while back. It’s pretty fast to apply it with a roller. I add a few extra coats to the tops and bottoms of the posts. And the ends of the rails.
The next day I can start to put everything together. I’ll be toe screwing the rails into the posts. Good enough for what is essentially a fencing project.
A single screw through the post saddle holds the bottom of the post in place while I clamp temporary braces to two sides. Then plumb the post with a spirit level. And I can repeat that on the second post.
Blocks clamped to the posts support the rails. And a long pipe clamp pulls the posts together as I run in the screws.
Working my way down the post I’ll next add the middle rail. Again, blocks support the rail while I bring the posts together with a pipe clamp. And run in more screws. And more screws.
Then the 2x6 bottom rail can be added.
Testing the fit of the Corrugated Galvanized Fence Panels
I had my roofing supplier cut these panels to 5 foot lengths. And I designed the surround fence so the posts were set apart about an inch greater than the panel widths. So I didn’t need to cut any metal for this. And I like that.
I added a corner brace between the mid rail to add some rigidity to the ends of the surround. If there’s too much movement I can add another brace to the top rails later. But I think it’s good enough like this.
The next day I added the panels. Eighth inch spacers lift the panel a bit to center it vertically. I used 1″ roofing screws that have a metal and rubber washer. This went quickly and I was done in less than an hour. I think taking the time to cut the rabbit in the top and bottom rails, so the panels are recessed flush, is worth the extra time. We though it looked pretty sharp.
I covered all the tank plumbing in part 2 of this series but I forgot to add a vent.
Rainwater Tank Vent
For this I bought an RV tank vent and fitted it with a bug screen. I cut a disc of aluminum window screen and siliconed it to the base of the vent.
I cut a hole in the top of the tank with a hole saw. Added some silicone to the base of the vent and attached it with screws.
Our shallow irrigation well is over in this corner of the property. It has a water line running under the field toward the house and past this shed. A few years ago when we put in the garden I tied into this line and installed several hose bibs.
Connect the Rain Tank to the Garden Irrigation System
I have a pump to pull water from the rainwater harvesting tank and send it to the garden. The plan is to turn off the well pump and close it’s ball valve. Then turn on the tank pump. So it can take over watering when the drip irrigation timers come on in the garden.
The pump will be set up in the shed on the left there. And I’ll run a 1″ water line underground and tie into the garden system. I ran a string line between two stakes to mark my trench location.
I cut the sod with a spade. And enlisted some additional help on the other side of the fence by the garden taps.
I have to get down to the poly line to see how I’ll tie in the rainwater supply to it.
There’s nothing like digging to remind yourself that you are out of shape and need to up the cardio in your workouts.
In part 1 I roughed in a 1″ white PVC line under the curb and to the corner of the shed. I’ll now continue that line up and through the shed wall. This is the supply line from the rainwater harvesting tank.
A galvanized strap will keep it secure for now.
Where this line comes up through the pea gravel I’ll add an elbow and barb fitting. Then I’ll connect this to the ball valve at the bulkhead fitting with some flexible black poly pipe.
Next I’ll add the line that comes out of the shed from the pump through the wall. This will have a tap on it as it continues down the wall and underground.
Now it’s a matter of wrangling a roll of poly pipe into the trench. I’ll rough cut it to length and lay it in.
I’ll cut the existing supply line that comes in from the irrigation well and add a T. It’s a bit of muscle work to get it all to fit before I squeeze the poly pinch clamps.
Then on the shed side I run the poly pipe into the other barbed fitting and clamp it. All the outdoor plumbing is done.
I bought a half horsepower jet pump with a small pressure tank attached. It came with a 20/40 pressure switch. On at 20 psi and off at 40 psi.
Rainwater Tank Pump Modifications
I’ll swap that switch for a 30/50 with a low pressure cut-off. This will stop the pump if the tank runs dry or the pressure drops below 20 psi.
I’ll disconnect the wires then spin the switch off the pump housing. I’ll add a short nipple as the new switch does not come with one.
Since this is a season pump setup I opted to wire a 110 volt plug to the pump. So I can just plug it into a receptacle in the shed when I need it.
So here’s a schematic type layout of how I’ll plumb in this pump in the corner of the shed. The bottom line comes from the tank, and the top line goes to the garden.
I’ll add compression couplings and unions to aid in the initial glue up of the pipe and fittings. And to allow disassembly and draining of the system later. I also have a check valve so water can only flow from the rain tank and never back to it.
Coming out of the pump I’ll add a pressure gauge, a ball valve, a spin down sediment filter (to catch any debris from the tank), then another ball valve.
And here’s the system installed in the shed. I did add another check valve to ensure I kept water from ever backing up into the pump when I’m switching from irrigation well supply to rainwater harvesting tank supply.
I’m not a plumber but I think this will work okay.
So I hope you have enjoyed this post, and thank you so much for reading. If I make any further improvements or changes I’ll post them here.
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- 3″ PVC Gate Valve
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