Rainwater Harvesting Systems in Adelaide: Choosing the Right Tank and Pump

A rainwater harvesting system can help Adelaide homeowners make better use of the water that falls on their roof. But choosing the right system involves more than buying a tank and connecting a downpipe.

The amount of rainwater you can collect, the storage capacity you need and the pressure required at your outlets all influence how well the system works.

A tank that is too small may overflow during winter and run dry when your garden needs water. A pump that is poorly matched to the system may struggle to supply a sprinkler or multiple household outlets. And an indoor rainwater connection needs appropriate plumbing and a reliable backup water supply.

The best starting point is to answer three questions:

1. How much roof area will actually drain into the tank?
2. What will you use the rainwater for, and how often?
3. Will gravity provide enough pressure, or will you need a pump?

This guide explains how Adelaide homeowners can assess those requirements, avoid common installation mistakes and prepare for a discussion with a licensed plumber.

How Does a Rainwater Harvesting System Work?

A domestic rainwater harvesting system collects water from your roof, directs it through gutters and downpipes, stores it in a tank and supplies it to selected outlets.

A typical installation has several important components.

Roof Catchment and Gutters

Rainwater flows from the connected roof area into gutters and downpipes. The usable catchment area depends on which sections of the roof are actually connected to the tank.

Inlet Screening and First-flush Diversion

An inlet screen helps prevent leaves and larger debris from entering the tank. Some systems also include a first-flush diverter, which diverts the initial roof runoff before water enters storage.

Rainwater Tank

The tank stores collected water until it is needed. Its capacity, location and access arrangements influence both everyday use and future maintenance.

Pump and Controller

Where gravity cannot deliver adequate pressure, a pump moves water from the tank to the connected outlets. A controller manages pump operation and may incorporate protection against running dry.

Overflow Drainage

Once the tank reaches capacity, excess water needs somewhere suitable to go. A poorly positioned overflow can direct stormwater towards walls, foundations or areas where water pools. Where gravity drainage isn't possible, stormwater pump and overflow drainage solutions may need to form part of the design.

South Australian Government guidance includes requirements for overflow arrangements and mosquito-proof screening.

Source: South Australian Government - Rainwater tanks

Why the Whole System Matters

Consider a tank connected to only one small roof section.

Even if that tank holds 5,000 litres, it cannot store water that never reaches it. Increasing the tank size may achieve very little unless the connected catchment area is sufficient.

The opposite problem can also occur. A tank may collect plenty of water but supply a garden sprinkler poorly because the available pressure is inadequate.

Tank capacity, catchment area and outlet demand need to work together. Changing one component without checking the others can leave the original problem unresolved.

How Much Rainwater Can Your Adelaide Roof Collect?

The starting calculation is straightforward:

Rainfall (mm) × connected roof area (m²) = theoretical collection (litres)

One millimetre of rainfall over one square metre represents one litre of water.

The important detail is to use the horizontal projected roof area connected to the tank, not automatically the footprint of the entire house.

Example: an Adelaide Home with a 180 M² Roof

Suppose a house has 180 m² of roof area, but the proposed rainwater tank will initially receive runoff from only 60 m².

During a 20 mm rainfall event, the connected roof section receives a theoretical 1,200 litres.

It would be incorrect to size the system around 3,600 litres of collection unless the full roof area could actually drain into the tank.

These calculations also represent an upper limit. Actual collection is affected by losses, first-flush diversion, gutter arrangements and available storage space.

Allow for Water That Never Reaches Storage

For an illustrative calculation, assume 85% of the theoretical runoff reaches the tank.

A 60 m² connected roof area receiving 20 mm of rain would produce:

60 × 20 × 0.85 = 1,020 litres of estimated collection

The 85% factor is an example, not a guaranteed collection efficiency. Actual performance depends on the installation.

There is another important limitation: available tank space.

If a 3,000-litre tank already contains 2,600 litres, it can only accept another 400 litres before overflowing, regardless of how much rain falls.

Why Adelaide Rainfall Patterns Matter

Adelaide experiences seasonal variation in rainfall, with generally wetter winters and drier summers.

This creates two different considerations.

During wetter periods, a tank may fill frequently, making additional capacity useful if the stored water can be used later.

During a prolonged dry period, the important question becomes how long the available water will last.

The Bureau of Meteorology's Adelaide West Terrace climate records provide historical rainfall information, but annual averages should not be treated as a prediction of water availability during a particular dry spell.

For garden irrigation, the time between useful rainfall events can matter more than the annual rainfall total.

What Size Rainwater Tank Do You Need?

There is no single tank size that suits every Adelaide property.

A suitable capacity depends on how much water the roof can deliver, how frequently it will be used, the amount of space available and whether the system supplies indoor fixtures.

Estimate Your Daily Water Demand First

Consider a household that expects to use approximately 100 litres of stored rainwater per day.

These are simplified examples assuming a full tank, no additional rainfall and full usable capacity.

Actual supply duration will differ. Some water may be unavailable because of the outlet position or pump operating limits, and household demand may change significantly.

A family using rainwater for toilets and laundry, for example, needs to account for those uses as well as garden watering.

When a Larger Tank May Be Worthwhile

Before replacing an existing tank, look at how it behaves throughout the year.

If the tank regularly overflows and later runs dry: There may be an opportunity to capture and store more of the available rainwater. Additional capacity is worth evaluating.

If the tank rarely fills: Check the connected roof catchment and inlet arrangement first. A larger tank may offer little benefit if insufficient water enters the existing one.

If the tank stays full for long periods: The issue may be insufficient water use rather than insufficient storage. Connecting a suitable garden outlet or considering other approved uses may provide more value than adding another tank.

If demand is much greater than collection: Increasing storage alone will not create additional water. The connected catchment area and expected demand should be reviewed together.

Check Physical Installation Constraints

Tank size is not only a question of litres.

Before selecting a tank, consider:

• The available width, height and footprint.
• Gate, driveway and side-passage access for delivery.
• A suitable, stable base designed for the tank and site conditions.
• Nearby downpipes and achievable pipe routes.
• The overflow destination.
• Access for inspecting and cleaning inlet screens.
• Pump location, ventilation where applicable and maintenance access.

A tank may fit the available space but still be awkward to install or service.

It is also worth checking where future landscaping, paving, fencing or renovations might restrict access.

A good tank location needs to work after installation, not just on delivery day.

Do You Need a Rainwater Pump?

Not every rainwater tank requires a pump.

A tank with a suitably positioned gravity-fed tap may be adequate for filling watering cans or other low-demand tasks.

However, many garden and household applications require more pressure or flow than gravity alone can provide.

Choose the Pump Around What It Needs to Supply

The appropriate pump depends on both flow rate and operating pressure.

Flow rate describes how much water is delivered over time, commonly measured in litres per minute.

Pressure determines whether water can be delivered effectively through the connected pipework and outlets.

These are related, but they are not interchangeable.

Why Maximum Flow Alone Can Be Misleading

A pump's advertised maximum flow does not necessarily represent what it will deliver at the pressure needed by your sprinkler or household fixtures.

Available performance changes with the operating conditions, including the pressure the pump must generate.

When comparing pumps, ask the installer:

What flow can this pump deliver at the pressure my system actually requires?

A useful pump recommendation should consider:

• The required outlet pressure and flow.
• Pipe length, diameter and fittings.
• The height difference between the tank and outlets.
• Whether multiple outlets may operate together.
• Pump starting and stopping behaviour.
• Protection against dry running.
• Servicing and access requirements.

Example: Garden Watering and Laundry at the Same Time

Imagine a household that wants to run a garden sprinkler while the washing machine is filling.

A pump selected only for the sprinkler might not provide adequate performance when both outlets are operating.

The solution is not automatically to install the largest available pump.

The plumber needs to assess the combined demand, pipework and operating pressure, then select an appropriately matched pump and controller.

Oversizing equipment can introduce unnecessary cost and may not address restrictive pipework or other system limitations.

Mayfair Plumbing provides pressure pump installation services in Adelaide.

What Happens to the Toilets or Laundry When the Tank Runs Dry?

For a garden-only system, running out of rainwater may simply mean waiting for further rainfall or using another available water supply.

An indoor rainwater system needs more careful planning.

Where rainwater supplies toilets or laundry fixtures, the arrangement should account for periods when the tank is empty.

Depending on the approved plumbing design, a system may use an appropriate mains-water changeover or an approved top-up arrangement.

These arrangements are not identical, and their behaviour can differ during pump or power failures.

Two Questions Every Homeowner Should Ask

1. What happens when the rainwater tank is empty?

Ask whether the connected fixtures continue receiving water automatically, whether a controller operates the backup and how the system indicates its operating mode.

2. What happens when electricity to the pump is unavailable?

An automatic mains-water backup does not necessarily mean every connected outlet will continue functioning during a power cut.

The answer depends on the equipment and plumbing configuration.

Before installation is completed, ask the plumber to demonstrate the arrangement and identify the fixtures connected to rainwater.

Keep Rainwater and Drinking-water Plumbing Properly Separated

Connections involving rainwater and the mains drinking-water supply must use appropriate approved arrangements and backflow protection.

Backflow protection helps prevent water from an alternative supply entering the drinking-water system. Where a testable device is installed, ongoing backflow prevention device testing may also apply.

The required protection and connection design depend on the installation and applicable plumbing requirements.

Do not attempt to connect rainwater pipework directly to the drinking-water supply yourself. Have a licensed plumber assess and complete the relevant work.

For state guidance, refer to South Australian Government - Rainwater tanks.

What Are the Rainwater Tank Requirements in South Australia?

Rainwater harvesting can be a practical choice for existing homes, but some building projects also have specific additional-water-supply requirements.

South Australian Government guidance identifies requirements for new homes and certain alterations or extensions.

For relevant alterations and extensions, the guidance refers to work greater than 50 m² that includes a toilet, water heater or laundry cold-water outlet.

A plumbed rainwater tank is one way of meeting applicable additional-water-supply requirements.

The government guidance describes a minimum tank capacity of 1 kilolitre (1,000 litres), with connection to specified indoor uses.

Those uses include a toilet, water heater or all cold-water outlets in the laundry, as applicable to the requirements.

Does Every Adelaide Home Only Need a 1,000-litre Tank?

No.

The 1,000-litre figure should not be treated as a universal installation specification.

Planning provisions, approved building documents and site-specific stormwater requirements may impose different conditions.

For example, a development may need to address both:

• Rainwater reuse: storing water that will later be used by the household.
• Stormwater detention: temporarily holding runoff to manage its discharge.

These perform different functions, even where they form part of a combined system.

A tank intended to satisfy water-reuse requirements should not automatically be assumed to satisfy a separate detention requirement.

What to Check Before Ordering a Tank

Review the approved plans and relevant conditions for:

• Required rainwater storage or additional-water-supply provisions.
• Any separate stormwater detention obligations.
• Minimum connected roof catchment area.
• Required indoor plumbing connections.
• Overflow and stormwater discharge arrangements.
• Applicable approvals and plumbing compliance documentation.

Where the relevant work requires licensed plumbing, engage an appropriately licensed professional and ensure required documentation is completed.

The South Australian Government rainwater tank guidance is a useful starting point, but the approved documents and requirements applicable to the individual property must be checked.

What Should a Rainwater System Installation Quote Include?

Two rainwater installation quotes can look similar in price while covering very different amounts of work.

One quote may include the tank and basic connections. Another may include pump controls, downpipe modifications, overflow drainage, indoor plumbing and associated installation work.

To compare quotes meaningfully, give each installer the same requirements.

Rainwater Installation Quote Checklist

Compare Garden-only and Indoor-connected Options

For an existing home, consider requesting two clearly separated prices.

Option A: Garden-only rainwater system

This may include a tank, garden outlet and, where required, a pump.

Option B: Garden and indoor rainwater system

This may add plumbing to selected toilets or laundry outlets, additional controls and a suitable mains-water backup.

Comparing both options helps identify the cost of the additional connections rather than assuming the tank itself is the major expense.

If laundry renovations, paving replacement or other building work is already planned, ask whether pipework can be coordinated with that project.

Running pipes before walls or paths are finished may avoid unnecessary rework, subject to the installation requirements.

How Much Money Could Rainwater Harvesting Save?

Water savings depend on how much mains water is actually replaced.

Consider a home that uses 20,000 litres of harvested rainwater annually instead of mains water.

20,000 litres = 20 kilolitres.

At an illustrative variable water usage charge of $3 per kilolitre:

20 × $3 = $60 in annual usage-charge savings.

This is an example, not a forecast for an Adelaide property or a statement of current SA Water pricing.

Actual savings depend on rainwater availability, connected uses, demand and the water tariff that applies.

Pump electricity, maintenance, equipment replacement and installation costs also need consideration when assessing financial value.

A connected property's fixed mains-water supply charges do not disappear merely because rainwater is used.

Check the current SA Water residential water prices and use your actual water usage to estimate the potential benefit.

A rainwater system can have practical benefits beyond direct bill savings, but those benefits should be weighed against installation and ongoing costs.

What If the Tank Is Full but the Taps Have Little or No Pressure?

A full tank does not guarantee that connected outlets will receive adequate water pressure.

When performance suddenly changes, the first step is to identify what has stopped working.

Check Which Outlets Are Affected

Only one garden tap has poor flow: The problem may be associated with that particular outlet, hose, filter or section of pipework.

Every rainwater-connected outlet has poor flow: This suggests checking components shared by the outlets, such as the pump, controller or supply arrangement.

The pump operates repeatedly when no outlets are being used: Unexpected cycling can indicate a fault that requires investigation.

The pump runs but delivers little or no water: Possible causes include an inadequate water supply to the pump, an obstruction or a pump-related fault. The cause cannot be identified reliably from this symptom alone.

Safe Observations Before Calling a Plumber

Homeowners can often collect useful information without opening equipment or altering plumbing.

Note:

• The approximate water level in the tank.
• Which connected outlets are affected.
• Whether the problem happens continuously or intermittently.
• Any visible fault indication on the controller.
• Whether the pump appears to start and stop frequently.
• Whether the symptoms began after a power interruption or other event.

If a pump is not delivering water, avoid repeatedly resetting it or allowing it to continue operating against an apparent fault.

Do not open electrical components, bypass safety controls or dismantle pressurised equipment.

Mayfair Plumbing's guide to signs a water pump needs repair or replacement provides additional information about common pump problems.

Routine Rainwater System Maintenance

Regular visual checks can help identify issues before they become more serious.

Keep accessible inlet screens clear of debris, inspect mosquito mesh for damage and check where the overflow discharges after heavy rainfall.

Look for blocked gutters, damaged screening and standing water around the tank.

SA Health recommends maintaining screens, pipes and gutters and ensuring that overflow water does not create mosquito breeding conditions.

Source: SA Health - Managing mosquitoes in rainwater tanks

For pump servicing, repairs and changes to plumbing connections, seek advice from the relevant qualified professional. Periodic rainwater tank pump servicing can help pick up worn seals, failing pressure switches and controller faults early.

Need Help with a Rainwater Tank or Pressure Pump in Adelaide?

Choosing the right rainwater system begins with understanding what your property can collect and what you want the stored water to do.

A garden-only installation may have relatively simple requirements. Supplying household fixtures or multiple outlets introduces additional considerations around pump performance, water backup, pipework and plumbing compliance.

Before speaking with an installer, it helps to know:

• Where a tank could be positioned.
• Which downpipes are nearby.
• What outlets you want to supply.
• Whether you have an existing tank or pump.
• Any current problems with pressure, flow or water availability.

For an existing pump fault, photographs of the equipment label and controller can also help explain the system.

Mayfair Plumbing provides rainwater pump installation and related plumbing services in Adelaide.

Call Mayfair Plumbing on 0429 361 819 or discuss your rainwater system requirements with our team, including an existing pump that is not delivering water as expected.

References and Further Reading

• South Australian Government - Rainwater tanks
• Bureau of Meteorology - Adelaide (West Terrace) climate statistics
• SA Health - Managing mosquitoes in rainwater tanks
• SA Water - Residential water prices