Rainwater Harvesting

Notes from the Pinehaven Community Hall Rainwater Harvesting Workshops, held February-March 2011

Written by David Brown, April 2011

A "how to" on building a (non potable)rain water collection system for the home garden Brought to you by:

Pinehaven Progressive Association (Max Christensen and David Brown) with assistance from Paul Kennett, Matti Givon and Stan Abbott.
Transition Town Upper Hutt (Pat van Berkel)
Upper Hutt City Council (Enthusiasm and funding)

You can visit the site to view how the tank is constructed. The location is 7A Forest Road, Pinehaven, Upper Hutt.

Day 1 - build platform

Day 2 - install tank and connect up

PLATFORM CONSTRUCTION

Attach:fig1-platform-height.gif Δ|Figure 1 Platform Height

We begin platform construction by choosing a suitable location and establishing a finished platform height. See Figure 1 Platform Height.
Dig 4 post holes 350x 350x450 deep to the dimensions of the tank corners. In our case for a 1000ltr tank the dimensions were 1.000m x 1.200m x 1.200m high.
Set the posts securely and brace as required to keep straight and square. Make sure there is adequate side cover and at least 100mm below the post bottom for concrete. (Ensure the 100mm gap underneath by inserting a stick or similar to act as a separator.)
Mix the concrete and place into the holes and around the posts. A vibrator is not needed to settle pre-mix/instant concrete but use a spade or similar to work the concrete around each post. Give it a few days to harden then remove the formwork and supports.
Trim the tops of the posts to the same level (150mm below the finished platform height).
Install the 100x100x1200 bearers onto the post tops- it helps to pin them in place with a couple of 100x4.00 nails- then secure to posts with sws600mm straps bent over bearer and down posts ( 2 straps per post). Nail off with bracket nails.
Cut 6 100x50x1000 long horizontal supports and place 2 at each end and 2 in the middle, 50mm side on sides (100mm side on top), and spaced about 20-25mm apart. Nail them to bearers with 100x4.0 galvn flathead nails.
Install diagonal braces as shown in Figure 2 Platform Structure. With the bottom edge about 150mm above the ground, pin in place with 100mm nail. Drill a 6mm hole through brace and into post and fix with 10x120mm coachscrew and square washer each end.

Attach:fig2-platform-structure.gif Δ|Figure 2 Platform Structure

Stand back and admire.

TANK AND PLUMBING

Flush and clean out tank prior to start.
We begin the plumbing while the tank is on the ground for ease of access.
Determine where the inlet on the top of the tank is to be and cut an 80mm hole. Insert an 80mm round dropper from the inside of the tank note- trim about 8-10mm off the dropper, this will give a better fit when attaching the adapter. Drill 3mm holes through the tank and dropper flange in the corners making sure you are not too close to any edge. Fix in place with the stainless steel screws.
Using the 80/65 adapter apply Marley cement around the dropper where it comes through the tank and to the adapter. Fit the adaptor over the dropper applying pressure from both sides.
Repeat this procedure for the overflow on a side of the tank, near the top.
The vent can now be fitted by drilling a hole in the tank and fitting the Marley vent. We made our own vent but at the end of the day it is simpler to just buy the vent.
Lift the tank onto the platform.
Secure by wrapping a sws600strap around the wire cage and pallet rail and nail off onto the bearer. Do this in at least 4 locations (for earthquake stability).
At the rainhead where the rain water discharges from the gutter remove the existing downpipe.
Fix the leaf eater (leaf filter) under the rainhead dropper and fix to the fascia with 2 stainless steel screws.
Using a selection of socket bends and 65mm pipe fix a run from the leaf eater to the inlet of the tank. In our case from the leaf eater we used an 80/65 adapter, small 65mm pipe spacer to 88 socket bend to a length of 65mm pipe to another 88 socket bend and a length of pipe to the inlet. If the run to the tank is long attach a support bracket as necessary. We dry fitted everything and left it like that but you could cement the joins if you like (but leaving it dry fitted eases future changes).
A useful addition is to install a first flush diverter. While this is not necessary if the water is only for non-potable uses such as the garden and toilet-flushing, it will be helpful in emergency situations when the mains water supply is not functioning.
The overflow is fitted the same way. We used a small 65mm spacer pipe to an 88 socket bend to a length of pipe to another 88 socket bend to the existing downpipe which discharged to the city stormwater system. Secure as necessary.
Next take the cap and drill a 30mm hole through the centre and install the 19mm tub outlet and place cap back on the tank.
Using small joining pieces of 19mm tubing attach to tub outlet 19mm elbow to 19mm in line valve to 19mm filter. The filter is required to ensure the water to the drip irrigation is clean of particles. Run 19mm tubing to garden and attach to selected drip irrigation. We are using drip irrigation tubing supplied by Megason Irrigation. It’s a tube with a very sophisticated hole - it filters and maintains equal pressure at the beginning and end of the run. At a later date a grid and valve system will feed each of the garden plots.

This completes the installation of a 1000ltr garden watering system. These instructional directions, diagrams, material lists and photos will get the DIY’er up and watering.

NOW wait for the next decent rain and marvel at how quickly the tank fills and how much water can actually be collected and used more efficiently thus taking a load off the existing infrastructure. Its simple, efficient and feels good. Have fun and GO DO IT.

Written by David Brown, April 2011

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Page last modified on April 26, 2011, at 03:25 am