Catching What Falls From the Sky
A 200-square-metre roof in Canberra can harvest around 120,000 litres of rainwater annually. That's roughly half of what the average household uses. It's also water that falls freely, requires no treatment plant to produce, and arrives at your property already. The only investment is in capturing it instead of letting it run down the storm drain.
Rainwater harvesting makes particular sense in Canberra. Water restrictions during dry periods limit how and when you can water gardens. Mains water isn't getting cheaper. And there's something satisfying about being less dependent on external supply, about knowing that your garden will survive water restrictions because you've planned ahead, about reducing your demand on shared water resources.
The tank itself is just the container. What makes a rainwater system useful is the plumbing: how water gets into the tank, how it gets out to where you use it, how the system behaves when the tank is full or empty, and how it integrates with your existing mains supply. This is where professional plumbing makes the difference between a system that works reliably and one that frustrates.
A well-designed rainwater system captures water efficiently, delivers it where you need it at useful pressure, protects water quality through appropriate filtration, and switches seamlessly to mains backup when the tank runs dry. It requires minimal intervention from you once installed, quietly doing its job through wet seasons and dry.
From Roof to Tank
Getting water from your roof into your tank seems straightforward, but the details matter for water quality and system efficiency.
Gutters and downpipes are your collection system. Clean, well-maintained gutters catch water effectively. Clogged gutters overflow, sending water straight to the drain rather than your tank. Leaf guards reduce debris entering the system, though they need periodic cleaning themselves.
First flush diverters capture the initial runoff from each rain event and direct it away from your tank. The first water off your roof carries accumulated dust, bird droppings, leaf residue, and other contaminants. Letting that first flush bypass the tank significantly improves stored water quality. The diverter fills with contaminated water, then automatically directs subsequent cleaner water to the tank.
Tank inlets include strainers that catch debris the first flush system doesn't. Leaves, twigs, and larger particles get filtered here before entering the tank. These strainers need periodic cleaning, especially after storms that bring down significant debris.
Multiple downpipes can feed a single tank, maximising capture from your entire roof. The plumbing connects collection points through appropriately sized pipes that handle the flow from heavy rain without backing up. If only some downpipes feed the tank, choose those from roof areas least affected by overhanging trees or other contamination sources.
Overflow management directs excess water when the tank is full. Water needs somewhere to go during heavy rain after the tank fills. Overflow typically connects to the stormwater system or disperses into landscaping. The overflow design prevents backpressure that could affect collection and avoids creating erosion or pooling problems.
Tank Selection and Placement
The tank itself isn't plumbing work, but tank choices affect what plumbing is needed and how well the system performs.
Tank size should match your roof area and intended use. Too small, and you'll empty the tank quickly during dry spells. Too large, and you've spent money on capacity that rarely fills. For garden watering only, modest tanks often suffice. For toilet and laundry supply, larger tanks maintain supply through extended dry periods.
Tank location affects plumbing complexity and cost. Close to downpipes means simpler, cheaper collection plumbing. Close to usage points means simpler, cheaper distribution plumbing. Where these conflict, the tradeoff depends on your specific situation. Underground tanks offer aesthetic benefits but add excavation cost and pump requirements.
Tank material options include polyethylene (most common), concrete, steel, and fibreglass. Each has advantages and limitations. Your plumber can advise on compatibility with different plumbing configurations but generally works with whatever tank you choose.
Access for maintenance matters. Tanks need periodic inspection and occasional cleaning. Inlets, outlets, and overflows need accessible connections. Think about how you'll service the system over its lifetime, not just how it looks on day one.
Elevation affects whether you need pumping. Tanks positioned above their usage points can supply by gravity, simpler and cheaper than pumped systems. For most configurations, however, pumps are necessary to deliver water at useful pressure to toilets, washing machines, and taps.
Pumping and Pressure
Unless your tank sits on a tower, you'll need a pump to deliver rainwater at useful pressure. Pump selection and installation significantly affect system performance.
Pump types for rainwater include external pumps (mounted outside the tank), submersible pumps (inside the tank), and pressure systems (pump plus pressure tank). External pumps are easiest to service but need weather protection. Submersibles are quiet and protected but require accessing the tank interior for service. Pressure systems maintain consistent pressure and reduce pump cycling.
Pump sizing depends on required flow rate and pressure. A pump supplying only garden taps needs less capacity than one running toilets, washing machine, and multiple outlets. Undersized pumps can't deliver adequate flow. Oversized pumps cycle frequently, shortening lifespan.
Automatic operation is standard. The pump starts when you turn on a tap or a toilet refills, then stops when demand ceases. Pressure switches or electronic controllers handle this cycling. Good controllers also protect the pump from running dry if the tank empties.
Noise matters if the pump is near living areas or bedrooms. Some pumps are quiet; others aren't. Location and housing options can reduce noise transmission. Discuss noise concerns with your plumber before finalising pump selection and placement.
Electrical connection requires appropriate wiring and protection. Pumps need power supply; outdoor installations need weatherproof connections and safety switches. Electrical work typically coordinates with plumbing installation.
Where Rainwater Goes
Different uses for rainwater have different requirements. Understanding what you're supplying helps design the right system.
Garden watering is the simplest application. A tap connected to the rainwater system provides manual watering. Connected to irrigation controllers, the system waters automatically. Water quality requirements are minimal since you're watering plants, not people.
Toilet flushing saves significant mains water. Toilets use about 20% of household water, and there's no need for that to be drinking quality. Rainwater plumbed to toilets displaces mains water for every flush. The plumbing connects the tank supply to toilet cisterns, with appropriate backflow prevention.
Laundry supply extends savings further. Cold water for washing machines can come from rainwater, reducing mains consumption for laundry. Rainwater is actually softer than Canberra's mains water, potentially improving washing performance and reducing detergent needs.
Hot water supply is possible but less common. Using rainwater for your hot water system doubles its use, but requires ensuring supply reliability and may affect system warranties. Some households connect rainwater to hot water; others choose to keep hot water on mains supply for simplicity.
Whole-house supply, including drinking water, is achievable with appropriate treatment. UV sterilisation and filtration can bring rainwater to drinking quality. This level of treatment adds cost and complexity but enables rainwater to supply every tap in the house.
Mains Water Backup
Tanks run dry during extended dry periods. Unless you're prepared for no supply when that happens, you need a system that switches to mains water when rainwater runs out.
Manual changeover is the simplest approach. When the tank is low, you physically switch valves to use mains water instead. This requires monitoring tank levels and remembering to switch. It's workable but requires attention.
Automatic mains switching devices handle changeover without intervention. When tank level drops below a threshold, the device switches supply to mains. When rain refills the tank, it switches back to rainwater. You never run out of water and never think about switching.
The switching device must include an air gap or appropriate backflow prevention. This is a regulatory requirement preventing rainwater from potentially contaminating the mains supply. The air gap ensures that mains water can flow into the system but stored rainwater can never flow back into mains pipes.
Different switching devices suit different situations. Some are small units suited to simple systems. Others are more sophisticated, handling multiple supply scenarios. Your plumber recommends appropriate devices based on your system design.
The mains connection itself is plumbing work requiring compliance with water authority requirements. Icon Water has specifications for how rainwater systems connect to mains supply. Your plumber ensures the installation meets these requirements.
Water Quality Considerations
Rainwater quality depends on your roof, your collection system, and your storage. A few elements maintain quality for different uses.
Roof material affects water quality. Concrete tiles, Colorbond, and glazed tiles are generally fine. Some older roofing materials may leach contaminants. Lead flashings can be a concern. If you're uncertain about your roof, water testing can confirm suitability.
First flush systems, as mentioned earlier, are the first line of quality protection. They're simple, passive, and effective at removing the most contaminated initial runoff from each rain event.
Tank screens at inlets prevent debris entering the tank. Finer mesh catches more, but clogs faster. Regular cleaning maintains effectiveness.
In-tank conditions affect stored water. Light promotes algae growth, so tanks should be opaque or covered. Mosquito-proof screens on inlets and overflows prevent breeding. Keeping the tank reasonably full reduces the significance of sediment that accumulates on the bottom.
Filtration before use removes particulates that made it past earlier stages. Sediment filters are standard for pumped systems, protecting both the pump and outlets. Finer filtration suits uses where clarity matters.
UV sterilisation kills bacteria and other microorganisms, making water safe to drink. For toilet and laundry use, sterilisation is unnecessary. For drinking supply, it's essential. UV units install in the supply line after filtration, treating water immediately before use.
Installation Process
Rainwater plumbing typically proceeds in logical stages, though the specifics depend on whether you're plumbing a new tank or connecting to existing infrastructure.
Design consultation establishes what you want from the system and how to achieve it. The plumber assesses your tank (or tank site), identifies collection points, determines usage points, and plans the piping routes. This planning stage shapes everything that follows.
Collection-side plumbing connects downpipes to the tank through first flush devices and inlet filters. This may require modifying existing downpipes and running connecting pipes along the building or underground.
Pump and equipment installation puts the delivery system in place. The pump, pressure controller, filtration, and switching devices install according to the system design. Electrical connection enables pump operation.
Distribution plumbing runs from the rainwater system to usage points. For toilets and laundry, this means running new supply lines, potentially through wall cavities or roof spaces. Garden taps may need only short runs from the pump.
Commissioning and testing verifies everything works correctly. The plumber tests for leaks, confirms pump operation, verifies switching function, and ensures appropriate flow to all connected outlets.
Compliance certification documents that the installation meets requirements. This certification matters for insurance purposes and if you ever sell the property.
Maintenance Requirements
Rainwater systems need periodic attention to maintain water quality and reliable operation.
Gutter and strainer cleaning prevents debris buildup that affects both collection efficiency and water quality. How often depends on your environment, more frequent if you have overhanging trees.
First flush devices need draining and occasional cleaning. Most have simple drain valves. After cleaning, they're ready for the next rain event.
Filter replacement maintains water quality and system flow. Sediment filters clog gradually and need periodic replacement. How often depends on your water quality and usage.
Tank inspection every few years confirms tank condition and accumulated sediment levels. Most tanks eventually need cleaning to remove sediment that builds up over years. Professional tank cleaners can do this without emptying the tank entirely.
Pump service keeps the delivery system reliable. Annual checks catch issues before pump failure leaves you without supply. Pumps eventually wear out and need replacement, but well-maintained pumps last many years.