Why do I call my rainwater system "free"?
One-off expenses for system (not counting the 2 weeks of work I put into
it) : NZ$300
We pay about NZ $30 per year for the little amount of city water
we use as drinking water.
(Our roofs are corrugated iron painted with metal-containing paint, hence
the water from the roof is not recommended for drinking).
Savings by using hardly any city water: about $200 per year (increasing
every year because
city rates for water are rising rapidly).
Hence after 15 years the whole rainwater system has paid for itself and
actually MAKES MONEY at a rate of about $200 per year!
Advantages and incentive: - gentle on mother earth
- use of natural resources instead of relying on expensively filtered
and chlorinated drinking water.
- no valuable drinking water used for toilets, washing machine,
dishwasher, shower, handwashing and gardening (except hot water,
which is still city water in our case)
- always minimum water bills (we pay about NZ $30 per year).
- our rainwater tanks (6,400 litres together ) are a buffer for rainwater,
- less sewage overflow onto our swimming beaches
- less stormwater drainage necessary to build in the city
- less overflow of canals and city pipes.
- city drinking water gets cleaner because more good city water is available
less need to filter dirty river water for our city water
What did I need to buy?
- 4 round black plastic tanks (rotational moulding, 800 litres each)
- 3-stage pump (with 8-litre-buffer tank) producing 40 psi pressure.
- black plastic piping, connections, backflow valves
- 4 main valves at tank outlets
- large-diameter (6cm?) white PVC pipe from tanks to pump.
- rainwater pipes leading from gutters to tank (held up simply by loops
of number eight wire).
- special glue to connect rainwater pipes feeding the tanks.
- overflow rainwater pipe leading from tank to drain pipe.
- "gutter hedgehogs" (see below)
- trellis made-to-measure to hide the tanks.
How is the dual system installed?
Since our 4BRM house has crawling space underneath, I could easily install
the rainwater feeding pipes, overflow pipe and the high pressure pipes
underneath the house.
Under every sink and next to every toilet, the city water pipe and the
rainwater pipe are joined and then guided to the normal water outlet. The
rainwater connections have a backflow valve and a shut-off valve.
The backflow valve stops the city water accidentally flowing towards
the rainwater pump.
Similarly, the main city water pipe into the house needs a backflow valve
What is important to know about the tanks?
The tanks have to sit on 10-15 cm of sand in order to distribute their
weight onto the ground.
All tanks have big covers at the top (covering holes big enough for a
person to climb in; not that I ever do).
This is where I put in a few spoonfuls of chlorine every year. At all
other times the lids stay closed.
The rainwater is fed from several gutters through pipes underneath the
house towards one pipe which enters the first of four tanks through one
20cm hole at the top of the tank, not far from the manhole.
This first tank also is the one with the overflow pipe guided through
the outside wall near the top of the tank.
The tanks have one outlet at the outside wall near the bottom. This piping
is large white PVC (glued together).
The outlets are connected immediately to a large valve.
These large-diameter outlet pipes serve also as inlet pipes for three
of the four tanks, feeding water from the first tank to the others. Hence
the water level in all four tanks is always identical.
Connencted to this pipe is a small tap to allow the tanks to be emptied
into the garden (or to somewhere else with a hose).
A small wire mesh filter unit is installed just before this outlet pipe
enters the pump.
What is important to know about the pump?
Do not skimp on money for the pump!
A good pump creates higher pressure, lasts virtually forever and runs
nearly totally quiet.
Buy a 3-stage pump (i.e., one with 3 impellers) with automatic shut-off
when there is no water.
It should create 40 psi (same pressure as city water supply).
Mine is a GRUNDFOSS (presscontrol PC15) and cost about NZ$ 600.
You also should have a 8-litre buffer water cylinder attached to it,
otherwise your pump runs all the time when a tap in the house is dripping.
The cylinder keeps the pressure up for a while, so a dripping tap only starts
the pump occasionally.
Place the pump in a spot where you can easily detach it in case you have
to take it for repair (mine has never needed repair).
Also, have all connecting pipes flexible enough so they can be easily
I recommend that you buy half a metre of flexible water pipe (with
wire mesh exterior) from the plumbing shop for this purpose.
Have the power plug for the pump located near the pump to easily de-install
it when necessary.
Have a switch inside the house which allows you to switch off the pump
quickly if necessary.
Have a (large-diameter) valve about a metre away from the pump on the
inlet side for convenience (saving you from turning off all four taps at
the tanks when you detach the pump and creates less spillage in such cases.)
Is the rainwater being filtered?
Not well enough for drinking purposes.
Filtering means maintenance since the filters have to be changed regularly.
As I mentioned earlier, our roofs are corrugated iron painted with metal-containing
paint, hence the water from the roof is not recommended for drinking. For
drinking we use the city water.
I keep the rainwater in excellent (and basically drinkable) condition
by other, simpler means:
- "Gutter-hedgehogs" , which are wire with long bristles, placed
in the gutter before the downpipe.
- Down-pipe guards, which are plastic inserts at the top of the
- A small kitchen sieve at the inlet of the first rainwater tank.
- A woman's pantyhose wrapped around the small kitchen sieve to
stop algae and dust entering the tank. The pantyhose has to be cleaned or
exchanged about once every one or two years.
- I add a couple of spoonfuls of chlorine into each tank once a
Where did I put the tanks?
- I have space underneath a sundeck.
Don't they look ugly?
- I have covered them up with trellis, which you can get made-to-measure.
How long has the system been running?
- for 13 years
What problems have you had?
- Once the pump did not start after we were a long time away.
I disconnected it, PRIMED IT and reconnected it, and it
worked fine again. No expenses.
Priming means that you let the air out via a small allan-key
screw after connecting the pump to the rainwater supply.
This little bit of action is easy to forget, and the pump
will not run otherwise!
I calculated that the life expectancy of our pump is about
100 years, based on current usage.
(Since it contains water, it never runs hot.)
Can one come and have a look?
- you are most welcome.
More questions? - give me a ring (09-483-4211).