Gravity feed rainwater tank on a stand
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Gravity feed rainwater system

Way back in 2014, we listed ideas for a sustainable home design.  Libby suggested a gravity feed rainwater system to supply the toilets and laundry for 23B.  Instead of using electricity for pumping water to meet these needs, couldn’t gravity work for us?

Yes, gravity can do the job.  However, given that Libby herself now refers to the system as “Libby’s folly”, I wouldn’t recommend others be as brave and bold with their rainwater system.  We didn’t hit the original target with this one.

Missing the target

Gravity feed from a tank on a stand.

A gravity feed rainwater system is a simple concept.  Put the water tank on a stand and let nature take its course.

Water tank sitting on a stand can be a gravity feed system

When flushing a toilet, the cistern inlet valve opens and the rainwater flows downhill to fill the cistern.  No pumping so no electricity required.

Now it’s time for a bit of Science.  This is the bit we didn’t think too much about until late in the design process.  First, the water level in the rainwater tank must be a certain height above the inlet valve on the toilet or washing machine.  Too low and there isn’t enough pressure (head) to open the valve.  Next, the top of the tank has to be below the gutters so rainwater drains easily into the tank.

Guess what?  After testing, our plumber discovered the minimum water level was above the gutter height.

By this time, we’d committed to a 5 kilolitre rainwater tank sitting on a stand to gravity feed the toilets and laundry.  No turning back because we’d already invested in the piping infrastructure.  We forged ahead and overcame the problem by adding a small pump to get rainwater up into the tank.  Not quite the original idea …

Getting the tank onto the stand.

A white PVC pipe sticking out of the ground marks the spot where the gravity feed tank goes.  It’s in a corner of the garden, nestled into the trees growing along the back fence.

Overflow outlet pipe marks the position of the rainwater tank

The tank stand arrived first.  Getting a large steel structure on site wasn’t easy.  It’s lucky Joan is a good neighbour.  She allowed the delivery truck to back down her driveway next to our shared fence.

The truck’s crane lifted the stand over without damaging the new fence or hitting our house.  All good, but the stand was left upside down and a fair distance from the foundations.

New tank stand delivered and left upside down in the back garden

I don’t know how David’s crew managed to get the stand into the correct position and alignment.  They said, “That’s where the magic happens.”  I suspect it was a combination of leverage and brute force.

Rainwater tank stand right side up and in position ready to start on the gravity feed system

The plumbers were equally secretive about how they lifted the water tank onto the stand.  We went out to do our grocery shopping and returned to find the tank in position.  More magic!

Gravity feed rainwater tank in position on top of the tank stand

Ideally we wanted a corrugated iron tank which matched the recycled steel cladding on the north wall of 23B.  Cost knocked that idea on the head because a steel tank costs twice as much as a plastic one.

Once the plumbers finished connecting their pipes, David couldn’t resist the temptation to add a decorative feature.  He asked his apprentice, Corey, for ideas on creating something interesting with leftover concrete mesh reinforcing.  Here’s what Corey came up with – two diagonals of mesh running up the side of the stand.  Nice one!

Reo mesh used for decorating the tank stand


With so much going on during building, it’s possible one trade can “bump into” something installed by another.  The underground piping for the rainwater system is a good example.

Murphy's Law in action

Early in the 23B build, rainwater falling on the roof came out the end of the collection pipe.  In the last few weeks of construction I discovered it wasn’t anymore.  Where was the water going instead?  Oh no, we had a leak in the underground piping!  What had changed?  It took a while, but the plumbers found a couple of issues, including a leak caused by excavations for the rear deck.  A bit of plumbing surgery fixed the problem.

Leak in the collection pipe for the rainwater collection system

Gravity feed system operational.

Let’s follow the rainwater to find out how it ends up in the big tank without relying on gravity to do the work.

All the rain falling on our roof is collected and piped underground to the garden shed at the back of the property.

Rainwater collection piping runs towards the garden shed at the back of the property

We use a “charged system” to get rainwater into a 2 kilolitre tank tucked away at the side of the shed. Charged is another way of saying a sealed system which is always filled with water up to the tank inlet. This means the gutter downpipes have the same water level inside. When it rains, there is an instantaneous flow into the tank because the pipes are water filled.

The small tank also collects rain falling on the shed’s roof.

Rainwater tank at the side of the garden shed supplies the gravity feed tank on the stand

Once a day, I use a TotalFlo pump to transfer water from this tank to the 5 kilolitre tank on the stand.  The pump uses electricity from the shed’s offgrid solar power system.  I’m using sunlight as my energy source.  The piping is a bit more complicated since the plumbers added flow options.  For example, I can send mains water to the 5kL tank if we ever run out of rainwater.

Pump transfers water from the garden shed tank to the gravity feed tank on the stand

A float valve controls water flow to the tank.  Once the level is high enough, the valve shuts off and then the pump stops.

Gravity feed tank sitting on a stand

What’s the answer to the obvious question, “Does it work?”  Yes, it does.  There is enough pressure in the system to slowly refill toilet cisterns and supply the washing machine.

Side benefit of a tank stand.

Although the gravity feed system doesn’t quite measure up to Libby’s original vision, we quickly noted one advantage for a tank on a stand versus sitting on the ground.

Hoisting a water tank into the air opens up more gardening space underneath.  We didn’t lose a significant patch of ground.  Also, a tank stand is the perfect structure to support climbing plants.  What could be better for growing loganberry and raspberry plants?

Tank stand is the ideal structure for climbing plants

Adding wire mesh to the base gives the young plants something to hang onto as they grow.  Libby is looking forward to future harvests as a source of tasty fruit for making jam.

Raspberry and loganberry plants getting started on wire mesh

Benefit of hindsight.

Looking back, we should have done something more conventional for a lower cost.

Benefit of hindsight looking the rear view mirror

However, where’s the fun in that?

Now we have a unique landscaping feature consisting of a rainwater tank stand and a productive berry farmlet.  It’s not something visitors expect when they look into the back garden.


  • Walt Graham

    June 08, 06 2023 08:07:41

    Just wondering if I might ask about your experience with water pressure from your system. I’m building a house on the south coast of NSW and have erected a 7500 high tank stand with an eye to avoiding having to use a pressure pump as you did. Now is the time to make the decision as to proceed down this route or to abandon the idea due to potential pressure issues. Would you mind having a chat?
    Thank you, Walt

    • Libby & Howard

      June 08, 06 2023 11:24:29

      Hello Walt,
      I discovered using a tank on a stand to gravity feed water to toilets and washing machine can be a risky proposition.
      Before the tank was installed and commissioned, the plumbers did test runs to find out what head of water was required to get a reasonable flow of water through the cistern valve. They sat on the roof with a bucket of water and ran a plastic pipe down to the cistern. That set the minimum height for the tank stand plus water level in the tank. Being in suburban Melbourne on a flattish block, there wasn’t much choice in where to put the tank + stand and there were also height considerations. Not a good idea to have a really tall stand towering over the neighbours.
      In rough numbers, the builder installed a 2.7m high stand with a tank that adds another 1.2m to the head of water (when it’s full).
      The test runs did produce an arrangement that works. However, toilet cistern refilling is slower than mains pressure. Not really a concern, so I’m happy with gravity feed. Avoids having a pump run every time someone flushes a toilet.
      Connecting the tank to the washing machine wasn’t something we tested. Took a leap of faith and just went ahead. It does work but, only just. The front end loader chugs along, taking longer to meet the requirement for water for its wash cycles.
      I discovered keeping the head tank full, or near full, most of the time is the secret to a happy washing machine. I think the tank water level falls to a point where the pressure isn’t enough to push enough water through the machine’s inlet valve to satisfy the washing cycle. Experience has shown the best way to get our washing machine to work with gravity feed.
      Would I do a gravity feed system again with the current set up?
      Toilets yes. Washing machine no.
      My advice would be to test if your stand is high enough to create sufficient head for the toilet cistern valve to work. Our supplier couldn’t say what the minimum operating pressure was and, I assume, the number is different for different manufacturers. If a test run is successful, my experience is that gravity feeding water to toilets does work in the long term. Fingers crossed, I haven’t had any supply issues.
      Hope that helps.

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