A rain to mains switch installation is what stops an empty rainwater tank becoming an empty kitchen tap, toilet cistern or washing machine supply. For Australian homes using tank water indoors, it is a practical safeguard that keeps selected services operating when dry weather, high household use or a pump issue reduces your stored water. Done correctly, it lets your property use free rainwater first, then move to mains water when required without compromising the safety of the town supply.
The key word is correctly. Connecting a rainwater system to mains water is not a simple matter of joining two pipes. Australia has strict plumbing and backflow-prevention requirements to protect drinking water, and the final installation should be completed and commissioned by a suitably licensed plumber. For systems with electrically powered pumps or controls, a licensed electrician may also be needed.
What a rain to mains switch does
A rain to mains switch, sometimes called a rainwater-to-mains changeover device, manages the water source feeding nominated fixtures. In normal operation, the pump draws from your rainwater tank. If tank water is unavailable, the switch changes the supply to mains water so the household can continue to function.
The fixtures connected to the system depend on your property and local requirements. A common setup supplies toilets, laundry cold-water taps and outdoor taps from the tank, with mains water acting as backup. Some rural and acreage properties use a different arrangement where rainwater remains the primary household source and mains water is reserved for selected backup needs.
A quality changeover system is designed to avoid cross-connection between tank water and drinking water. That separation is essential. It protects the public water supply and prevents stagnant or untreated water from entering mains plumbing.
Start with how your home uses water
Before choosing equipment or booking a rain to mains switch installation, identify which outlets are supplied from the tank and how much water they use. This prevents a common problem: buying a switch that suits a small toilet-and-laundry line when the pump is actually expected to support a much larger household demand.
A two-bathroom home with several toilets, a washing machine and garden taps may need considerably more pump capacity than a granny flat, shed or tiny home. Pressure requirements matter as well. If the shower, washing machine and toilets draw water at the same time, the pump and pipework must maintain acceptable pressure without frequent cycling.
Your tank size also changes the decision. A large tank with good roof catchment may supply a substantial portion of household demand through much of the year. A smaller tank in a dry area may need mains backup more regularly. The switch does not create water – it simply makes the changeover reliable when the tank reaches its set low-water point.
Pump compatibility matters
Many changeover units are intended for use with pressure pumps, but they are not all suited to every pump type, flow rate or control arrangement. The pump, switch and plumbing layout need to work as one system.
For example, a pump with its own automatic controller may require a specific connection method to prevent nuisance cycling or fault alarms. Some systems manage changeover electronically, while others use float valves, pressure sensing or a break tank arrangement. The best option depends on the existing pump, whether mains pressure is available, the required flow, and the plumbing rules that apply at the property.
If you are replacing an older pump, it is often worth reviewing the whole setup rather than fitting a new pump to an undersized or poorly arranged changeover system. Correct pressure, suitable pipe sizing and accessible isolation valves make a noticeable difference to day-to-day performance.
The safe way to plan a rain to mains switch installation
A site inspection or a detailed discussion with your licensed installer should cover the tank, pump, pipework and household outlets before any equipment is ordered. The aim is to confirm that rainwater and mains lines are clearly separated and that the right backflow protection is included.
Your installer will generally need to check the tank outlet location, pump position, available power, pipe routes, existing mains connection and the fixtures intended for backup. They should also look at where overflow goes and whether the tank has an effective leaf strainer, mosquito-proof screens and first-flush management. Poor water collection upstream can shorten filter life and create avoidable pump problems downstream.
In many cases, local water authority requirements, council conditions and the National Construction Code influence what can be installed. Requirements can vary between locations and property types, particularly where rainwater is connected to internal plumbing. Do not assume a system used at a mate’s place is compliant at yours.
Why an air gap or backflow device is not optional
Mains water must be protected from possible contamination. A compliant system uses approved measures to make sure tank water cannot flow back into the town supply, including when pressure changes occur in the mains network.
This is why a DIY connection using a basic tee fitting or manual valve is not an acceptable substitute for a purpose-designed changeover system. Even if it appears to work, it may create a cross-connection risk, fail inspection, affect insurance or cause expensive rework later. The money saved upfront is rarely worth the risk.
Choosing between automatic and manual changeover
Automatic rain-to-mains systems are the usual choice for homes where tank water feeds internal fixtures. They change over when the tank reaches a low level or when the pump can no longer draw water, then return to rainwater once an appropriate level is restored. For busy households, this removes the need to monitor the tank every day.
Manual changeover can suit limited applications, such as a shed, garden supply or a property where the owner is regularly on site and the plumbing remains fully compliant. It can cost less initially, but it relies on someone noticing the tank is low and operating the correct valve. That may be inconvenient during holidays, dry spells or when tenants are using the property.
Automatic systems cost more than a few valves and fittings, but their value is in reliability. Toilets still flush when the tank is low, the laundry keeps running, and you are less likely to run a pump dry. For a permanent home, that convenience is usually worth considering.
Allow for filtration and water quality
A rain to mains switch manages supply, not water treatment. If tank water is used for drinking, cooking or bathing, speak with a water treatment professional and your installer about appropriate filtration and disinfection. Sediment filtration, carbon filtration and UV treatment may be part of the answer, but the right setup depends on your roof catchment, tank condition, household needs and water test results.
Even where rainwater is only used for toilets and laundry, a pump protection filter or strainer is worthwhile. It helps stop grit, leaves and sediment reaching pump components, valves and appliance inlet screens. Filters need regular cartridge changes or cleaning, so install them where they can be serviced without dismantling half the system.
Installation details that save trouble later
The best installations are planned for maintenance, not just for the day they are fitted. Pumps and controllers should be protected from weather where required, mounted to reduce vibration and left accessible for servicing. Pipework should be supported properly, with isolation valves positioned so the pump, filters and changeover device can be worked on without shutting down the entire property.
Ask your installer to label the rainwater and mains lines clearly. It sounds minor, but clear labelling helps future plumbers, owners and tenants understand which supply serves which fixtures. Keep manuals, compliance documents and any commissioning notes with your property records.
It is also smart to test the changeover after installation. Confirm what happens when the tank reaches low level, whether mains backup reaches every nominated outlet, and whether the system returns to rainwater correctly. If you have a power outage, ask what the expected behaviour will be. Some setups need power to operate the pump and controls, while mains-fed backup arrangements may behave differently.
Build the system around dependable equipment
A reliable result comes from matching tank capacity, pump performance, filtration and changeover controls rather than treating each item as a separate purchase. This is especially relevant for new builds, major renovations and acreage homes where water demand can grow over time.
Central Coast Water Tanks has been trusted for over 30 years and can help customers compare quality rainwater tanks, pressure pumps, filtration and changeover equipment as part of one practical water system. Shop online and save on proven products suited to homes from the coast to country, then have your licensed tradesperson confirm the final design and compliance requirements.
A well-planned rain-to-mains setup should fade into the background: rainwater does the everyday work when it is available, mains water steps in when it is needed, and your household is not left guessing where the next load of washing or flush will come from.