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Our first Rainwater Storage cistern

The water tank in May, 2002

When we moved into the Railway Carriage an immediate priority was securing a source of drinking water. We could easily pump water from the dam but as this was often "contaminated" with cow manure and agri-chemicals, we wanted something better.

For months we would gather our 15 20-litre containers and collect water from sources we deemed "unpolluted". We learnt that, in today's environment, no source is unpolluted and so we decided to install a rainwater collection and storage facility.

This is how we did it - in what we felt were "challenging" circumstances.

Background

The only collection surface we had was the "shed" roof. It was underneath a canopy of growing eucalypts and the only site for a water tank was amongst these trees on a fairly steep slope. After some investigation it became obvious that the base of the tank could be no more than a metre in diameter. Our concern was that any wider would necessitate cutting roots which might weaken the trees hold - as we were living under these trees we wanted them to remain standing!

Another complication was the small difference in height between the gutter and the sink height where we wanted the water to be gravity-fed - under 1 metre. We had a choice then - install a pump or work within the confines of the metre head.

At this stage we were looking at a 1 metre high by 1 metre diameter tank - less than 800 litres of water storage. Eventually we decided a tapered tank would work best - giving more storage capacity within the same footprint and height limitations. It came as no surprise that conical rainwater tanks are not available commercially and we would have to build our own.

This is how we did it.

The design we came up with

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over 3,200 litres on a 1 metre diameter base and within a 1 metre head!

The footings in place

Concrete footings and domed base have been poured.

The drain pipe is visible as are the rebars which will be bent out to form the angle of the taper. One has already been bent to the ~60^o angle.

We dug the footings about 300mm deeper to increase the storage capacity.

First course of bottles laid

The shape of the tank is now defined by the rebars - octagonal rather than circular.

We used jam jars for the first layers as they are shorter and didn't require so much excavation to accommodate.

Wine bottles introduce a new challenge!

As the bottle courses came clear of the ground level (sooner at the 'front' than the 'back') we started using long-necked (wine, champagne etc) bottles which were much easier to come by.

They also had a much longer bearing surface which helped the 'cantilevering' of each layer.

However the necks were heavy enough to pull them down and we needed to support them until the mortar went off. Our initial solution was a string loop round the neck tied to the top rebar.

Laying a course.

Our final solution was a straight stick supported at both ends from the top rebar which the bottle necks could rest on - 2 ties to a side as opposed to one for each bottle.

A days lay complete - the tank is filled.

We could only lay one course per day as each layer of bottles needed a firm base.

We would fill the tank with dam water to just below the new course at the end of each day's work. This served to extend the curing time of the mortar and identify leaks in earlier courses.

The finished interior.

After 2 weeks we had the walls complete and were able to apply the final sealing coat to the interior - we used a mortar mix with 50% more cement to improve the water-tightness.

The Overflow mechanism

We had decided to use Champagne Magnums for the overflow - in order to get the maximum height/capacity in the tank we chose to extend the depth by using pipes.

The bottles have had their bases sawn off and plastic pipes are inserted from inside. These pipes are then brought to a common point which will determine the depth of the water storage.

The bases of the magnums were then filled with mortar and sealed.

Basic roof support framework

We needed a strong roof to resist the plummeting branches - a feature of most mature eucalypts. Moreover I wanted it maintenance-free - or as much as possible.

The solution we chose was a poured reinforced concrete roof. This allowed us to match the shape of the tank, include a manhole for access and build it as strong as we wanted!.

This required a supporting framework which would have to be removed later.

Second layer of framework complete

Around this time we had acquired a pile of used irrigation pipes - mostly cut into very short lengths. It seemed ideal - flexible enough to form a curved surface, light, expendable, easy to fit and (hopefully) remove and economical!

We used 38mm (1½") poly for the base and 12mm for the second layer (½") using nylon string to tie them together.

Almost ready to pour

The next layer was simple corrugated cardboard - appliance (fridge, washing machine etc) containers which had 2 layers of corrugations. Small cuts here and there allowed these large pieces to conform to the underlying curvature of the poly pipes.

We added a large hump in the middle (it seemed like a good idea at the time) - a cane chair base - and covered the whole lot in plastic.

First roof pour underway

8 pieces of timber round the edge were wired to the reinforcing and completed the formwork - with a row of sand-filled (to prevent them floating in the wet cement) jars around the edge to maintain the "bottle" construction.

We carted the cement down the slope in buckets and everything went well until we noticed that no matter how much cement we added - the roof didn't appear to get any thicker!!

A quick look inside revealed the cause - in our excitement we had forgotten to prop the roof - the central supports were missing. As each bucket of cement was added, the framework was sagging by the exact amount needed to accommodate it!

A frantic burst of activity ensued and we managed to get props in place to prevent further sagging! We were fortunate indeed that the whole lot hadn't collapsed! We do have a very strong roof!

First roof layer finished, overflow being tested

As the first roof layer cured we set about making sure the inlet and outlet mechanisms worked properly. The overflow, drain and supply outlets worked well right from the word go. The inlet was more challenging - again, due mainly to the position.

The main challenge came from the eucalypts - again - a constant stream of dead leaves would block the gutter and - if not removed regularly (weekly at most) taint the water. When they flowered the dead flower parts would create a fine black "dust" which necessitated a fine filter to strain out but this also would get blocked and prevent the water going into the tank!

We decided to use 3 filtering stages and a settling tank to ensure the cleanest water possible. One feature of the system was that it had to work in a light drizzle as well as a heavy downpour - not as easy as it sounded at first.

Completed structure - a perfect solution!

There you have it - a final, decorative, layer has been applied compete with gemstones, glass "objects trouvé" and oyster shells!

All in all we feel it is a perfect solution for what was, initially, a challenging "problem".

10 years later

the structure is "fading"
into the undergrowth -

Still catching and storing
rainwater without fuss.

10 years later - an archeologists' dream?

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