Harmony House





Clean healthy water is an essential ingredient for healthy living, and as such a good amount of thought deserves to go into getting a water collection system right. Our choices of stainless steel rainwater tanks, first flush divertors, self-cleaning overflow system and UV filtration should ensure a clean and relatively low-maintaince water source for decades to come. Read further through this page for more information on our aims, research, decisions and results, as well as our tips and advice summary, for this element of our project - our rainwater collection system.


Our aim was simply to fully provide for our household water needs on rainwater alone. As the street in our locality doesn’t have a council water supply connection, this aim was a necessity as well as our desire.


The first thing we discovered - which is very obvious when you think about it - is that it’s not just the size of your tank that matters, but a combination of your tank size, your expected annual rainfall, and your roof catchment area. It’s those three factors working together that dictate how much water you’re able to have on hand at any given point. Then of course your family water-use habits come into play to determine how long that water might last.

There’s a fantastic online calculator we found that’s free to use - The Tankulator - which provides an easy way to take into account all those relevant factors. This is a particularly useful tool when planing out your water catchment system from scratch, as things like tank size and roof catchment area can be varied to show you the results of different decisions you might make. You get to see in graph form how full your tanks are likely to be at different times of the year, allowing you to determine the best likely tank size for your situation (not too small so as to be running out of water, and not too large so as to be wasting money on unused capacity).

The Tankulator tool, provided by ReNew, is invaluable in sizing and planning your water catchment system

The Tankulator resource is provided by Renew (formerly the Alternative Technology Association). We found Renew’s magazines and online library of articles an invaluable research tool for many different aspects of our project.

The next area of research focused on tank materials, the four main choices being plastic, concrete, ColourBond, and stainless steel. Each choice has a different potential impact on water quality, a different expected lifespan, and different price point.

A choice also has to be made whether to have a ‘dry’ catchment system (where all sections of the inlet pipes to the tank are above tank height, such that they ‘run dry’ after the rain stops), or a ‘wet’ catchment system (where some sections of the inlet pipes to the tank may run underground, either for aesthetic reasons or physical set-up restraints, such that water remains in the pipes unless flushed out).

Lastly we looked at different add-on possibilities to improve the end quality result of our water. These included options like first flush diverters (which discard the first millimetre or so of rain, in effect giving the roof a wash down before any water starts entering your tank); so-called ‘water nymph’ systems (which allow water to be drawn from near the surface of your tanked water rather than the bottom layers which may contain sediment); self-cleaning overflow systems (where water is drawn from the base of the tank rather than the top during overflow, thus discarding water that contains more sediment); and of course filters of varying sizes (in terms of what size particle they allow to pass) and varying types (including carbon filters and UV filters).


It was a great advantage being able to use the Tankulator calculator before our final house plans were drawn up. It was via this process that we were able to clearly identify the benefit of merging our intended carports and sheds into a single roof catchment area with our main house footprint, in order to maximise our collection potential from any given rain. In this way all of our roof areas (main house, carports and sheds, totalling over 400m2) are utilised to collect rain, draining into the same collection tanks.

With the roof catchment area then known, and our annual rainfall plugged in, we calculated that a collection capacity of around 50,000 litres would provide us with a comfortable amount of water for our needs. This was then catered for in our final house plans: we have two side-by-side tanks of 27,000 litres each connected at their base (acting as a single collection unit of 54,000 litres), located conveniently in terms of inlet pipes and other design considerations.

The choice of tank material was an easy one for us. It’s clear from the research that the safest thing to keep water in is stainless steel, as it is an extremely inert material that gives nothing off to the water. All the other main choices (plastic, concrete and ColourBond) are shown to leech various amounts of various things over the long term, none of which we felt like drinking. And even though stainless steel is often thought of as the more expensive of those choices, it is the most durable and long-lived, meaning that over the long term (one of our main decision criteria) it becomes the cheapest choice. We were also lucky to find a very well-priced supplier in Luke Marendaz of Stainless Steel Tanks Pty Ltd. Not only are their stainless steel products excellent quality and value, but the customer service was really outstanding (and we don’t say that lightly). It also turned out that by going with stainless steel tanks through this company, we were able to customise dimensions very specifically, which resulted in numerous benefits for our water catchment system as a whole that we hadn’t expected.

Stainless steel water tanks are the most healthy and cost-effective way to store rainwater long term

For example, tank height wasn’t restricted to a number of pre-determined choices, but could be specifically set to maximise capacity for the height of our inlet pipes. Also our desire for a ‘dry’ catchment system (cleaner and easier, with much less in the way of maintenance issues) was enabled by the ability to customise the tank height and diameter to such a degree. All tank inlets and outlets were specifically located to fit in with our catchment system as a whole, including the pipe down the bottom which joins the tanks into one unit, but which can also be used to isolate one tank from another for cleaning purposes when necessary.

Other decisions we made included opting for a first flush diverter, a ‘water nymph’ water outlet, and a self-cleaning overflow system, which all add to improved water qualiy. Luke and his company were innovative and helpful in having all three of our chosen add-ons fit in with our system and aims.

A first-flush diverter discards the first wash of rain from the roof, improving the end quality of collected water

Lastly in our system, on the water line into our house, is a 200 micron filter (located before the pump to remove any sediment) and then a 20 micron filter and a 1 micron filter leading into a UV lamp disinfection unit to fully sterilise the water. This is an example of a ‘whole house’ solution, where all the household water is clean and fit for drinking, which we felt was more useful and practical than opting for a filter on a single dedicated “drinking water” tap within the house.

A UV filter further improves end water quality


Despite Luke’s forewarning that tanks look much bigger on their sides, when they turned up on the truck I honestly thought I must’ve accidentally doubled the measurements I gave him - there was no way they were going to fit! But he was right (both in his forewarning and in the job he’d done) and they rolled perfectly into spot, made as ordered.

Tanks look much bigger on their sides

It wasn’t long before I was avidly watching weather predictions and tapping on the outside of the tanks to monitor the slowly rising water level in the final months before we were due to move in.


Stainless steel can be a great look, and the tanks were no exception, but as with many aspects of our project, the test of whether we’d got all our decisions right or not would only come with actually living with the system.


The first thing we seem to have got right is the capacity. Using the tanks for household purposes only (with our large areas of garden watering coming via a separate source - see Landscaping - Natural Pond Habitat) we’ve so far not dropped beneath two-thirds full, even over the low rainfall summer months, which feels to us like a comfortable capacity buffer against any harsher seasons that may pop up.

The other decisions too seem to have been justified. The water is so clean-tasting, even without a carbon filter in the system anywhere, that it tells us the first flush diverters, water nymph outlet, self-cleaning overflow and various filters are all doing their part for the end result. We’re glad we put them all in. But it was that core decision, going with stainless steel tanks, that forms the basis of our healthy system and gives us long term peace of mind.


     - The online Tankulator calculator at is an excellent resource to help size your tanks for your given roof catchment area, location, and water-use habits.

     - Go for stainless steel tanks. They’re worth it from both a water quality point of view, as well as long-term value for money.

     -      We feel that additions like first flush diverters, water nymph outlets, self-cleaning overflow systems, and UV lamp disinfection units are all very worthwhile additions.