The BASIX Water section assesses how a proposed residential development will reduce its demand for potable water compared with the NSW residential benchmark.
The result is influenced by water-efficient fixtures, landscape areas, low-water-use planting, rainwater or other alternative water sources, pools and spas, and any central systems or common areas associated with the development.
A passing water result is not produced by one universal requirement. The appropriate combination depends on the project location, dwelling type, landscape demand, water systems and commitments selected within the assessment.
In Brief
How Does BASIX Assess Water Efficiency?
BASIX estimates the potable-water demand of a proposed residential development and compares it with a benchmark representing pre-BASIX residential water use. The applicable target varies by climate zone and can require a reduction of up to 40%. BASIX considers fixtures, landscaping, alternative water sources, pools and spas, and shared or central water systems. The selected measures become project commitments and must match the approval and construction documentation.
Knowledge Navigation
Understanding the BASIX Water Assessment
Water Target
What Does the Score Mean?
How the project is compared with the NSW potable-water benchmark.
Indoor Demand
Fixtures and WELS Ratings
How showerheads, toilets and taps contribute to the water result.
Outdoor Demand
Landscaping and Irrigation
How lawn, garden and low-water-use planting are represented.
Water Supply
Alternative Water Sources
Rainwater, stormwater, greywater and other recognised sources.
What Does the BASIX Water Section Assess?
The Water section estimates the potable-water demand associated with the proposed residential development under standardised occupancy and use assumptions.
It does not attempt to predict the exact future water bill of a particular household. Actual consumption will continue to depend on occupancy, behaviour, maintenance, rainfall and how the installed systems are operated.
The regulatory assessment considers several connected areas of water demand and supply.
Assessment Area 01
Fixtures
The water efficiency of showerheads, toilets, kitchen taps and bathroom taps.
Assessment Area 02
Landscaping
The amount of lawn and garden and any areas nominated for low-water-use plant species.
Assessment Area 03
Alternative Water
The collection, storage and reuse of rainwater, stormwater, greywater or other recognised water sources.
Assessment Area 04
Pools and Spas
Pool or spa volume, covers, shading and any nominated rainwater top-up arrangement.
Assessment Area 05
Common Areas
Shared landscaping, facilities and water uses associated with multi-dwelling developments.
Assessment Area 06
Central Systems
Central tanks, recycled-water systems and other shared infrastructure serving several dwellings or common uses.
Assessment Result
What Does the BASIX Water Target Mean?
The BASIX water result is expressed as a percentage reduction in potable-water use compared with the residential benchmark used by the assessment.
The benchmark is 90,340 litres per person per year, equivalent to approximately 247 litres per person per day. The project’s required reduction depends on its climate location and can range from 0% to 40%.
| Water Result | Meaning | Compliance Principle |
|---|---|---|
| Target | The minimum potable-water reduction required for the project location. | The project must achieve at least the applicable target before the Certificate can be generated. |
| Calculated score | The estimated reduction produced by the project’s selected fixtures, landscape and water systems. | A higher percentage represents a larger modelled reduction from the benchmark. |
| Commitments | The measures relied upon to produce the calculated result. | The nominated fixtures, tanks, connections and landscape measures must be delivered as documented. |
A project achieving exactly its target and a project exceeding it both satisfy the water requirement. The Certificate records the commitments associated with the selected design rather than creating unrestricted flexibility to substitute water systems later.
The BASIX Water Score Is Not a Future Water Bill
The BASIX score is based on standardised assumptions so different development proposals can be assessed consistently.
Actual household water use can vary because of:
- the number and behaviour of occupants
- shower duration and frequency
- appliance use
- garden establishment and maintenance
- seasonal rainfall
- pool evaporation and operation
- tank maintenance and pump operation
- leaks or poorly maintained fixtures
A BASIX-compliant home can still use substantial water if the systems are operated inefficiently. Conversely, careful occupants may achieve lower consumption than the modelled result.
The score should therefore be understood as a regulatory design assessment, not a guaranteed prediction of future metered consumption.
Indoor Water Demand
How Fixtures Contribute to BASIX Water Efficiency
BASIX uses the nominated water-efficiency ratings of the fixtures proposed throughout the development.
The principal fixture categories are:
- showerheads
- toilet suites
- kitchen taps
- bathroom and basin taps
More efficient fixtures reduce the estimated demand placed on potable or alternative water supplies. Showerheads and taps that use less hot water can also reduce the energy required for water heating and support the BASIX Energy result.
The ratings selected in BASIX are commitments. Products installed during construction must meet the nominated ratings and, where a specific shower flow range is entered, the installed fixture must satisfy that range.
Fixture efficiency can improve the water result, but it may not be sufficient by itself where the project has extensive landscaping, a pool or a higher water target.
What Are WELS Ratings?
The Water Efficiency Labelling and Standards Scheme provides a standard way to compare the water efficiency of regulated fixtures and appliances.
A WELS label generally displays a rating from zero to six stars together with a tested flow rate or water-consumption figure. More stars generally represent greater water efficiency within the relevant product category.
| Product Category | BASIX Use | Delivery Requirement |
|---|---|---|
| Showerheads | Entered by WELS rating and, where relevant, the nominated flow-rate range. | The installed products must satisfy the selected rating and flow commitment. |
| Toilets | The selected WELS rating influences estimated toilet-flushing demand. | Each installed toilet suite must meet the nominated efficiency requirement. |
| Kitchen and bathroom taps | The selected ratings affect estimated internal water demand. | Installed tap outlets should match or exceed the committed rating. |
| Appliances | Water-efficient clothes washers and dishwashers can be nominated for eligible unit developments. | The committed appliances must be provided where their ratings are relied upon by the assessment. |
Appliance credits are not generally available in the same way for single dwellings, groups of houses or townhouse developments. The applicable BASIX screens should be followed for the project type being assessed.
How Landscaping Affects the BASIX Water Result
Outdoor water demand can form a significant part of the BASIX calculation. The assessment therefore records the proposed areas of lawn and garden.
Relevant landscape inputs can include:
- the total area of lawn
- the total area of garden
- areas containing recognised low-water-use species
- private courtyards and gardens
- common landscaping in multi-dwelling projects
- the alternative water source used for irrigation
Reducing irrigated area or selecting suitable low-water-use planting can reduce estimated potable-water demand. However, the entered areas should represent the actual landscape design rather than being adjusted only to improve the score.
Where low-water-use plant species are nominated, the relevant areas should be shown on the plans and the landscape documentation should identify the species proposed for those areas.
A change from low-water planting to conventional lawn or higher-demand landscaping after approval can affect the basis of the water result and should be reviewed.
Multi-Dwelling Coordination
Private and Common Landscape Areas Must Be Separated
Townhouse, villa and apartment developments can contain private landscape areas associated with individual dwellings and common landscape areas maintained for the wider development.
Dwelling Level
Private Landscaping
May include private courtyards, gardens, lawns or planting areas allocated to one townhouse, villa or apartment.
Development Level
Common Landscaping
May include shared gardens, communal recreation areas, entry landscapes and planting associated with common driveways.
The landscape schedule and BASIX application should identify these areas consistently. A private courtyard should not automatically be entered as common property solely because the development is proposed for strata subdivision.
Which Alternative Water Sources Does BASIX Recognise?
Alternative water can reduce potable-water demand by supplying suitable non-drinking uses within the development.
| Water Source | General Description | BASIX Consideration |
|---|---|---|
| Rainwater | Water collected from non-trafficable roof areas and stored in a tank. | Assessed from tank volume, connected roof catchment and nominated uses. |
| Stormwater | Runoff collected from trafficable or other suitable site surfaces. | Permitted uses depend on treatment. Reuse storage must remain separate from detention volume. |
| Greywater | Wastewater collected from selected bathroom and laundry sources. | The acceptable uses depend on whether the water is diverted or treated and on relevant approvals. |
| Reticulated or recycled water | A recognised non-potable water supply delivered through a separate system. | Availability, permitted uses and connections should correspond with the serving authority. |
| Private dam | Stored surface water associated with an eligible site. | Available as a BASIX alternative water source for single-dwelling developments only. |
Different sources have different treatment, health, approval and connection requirements. A source should not be nominated for a use that is not recognised for that water type.
Groundwater, river water and ordinary on-site sewage-management systems are not automatically recognised as BASIX alternative water sources.
Common Water Strategy
Does Every BASIX Project Need a Rainwater Tank?
No universal rule requires every BASIX project to install the same rainwater tank.
A tank may be required where the assessment relies on rainwater to achieve the applicable water target. Another project may achieve its target through a different combination of fixtures, landscaping or recognised alternative water infrastructure.
Where a rainwater tank is used, BASIX can rely on:
- the tank capacity in litres
- the roof catchment area connected to the tank
- the water uses supplied by the tank
- whether the system is private or shared
- any overflow connection to another tank
- the relationship with existing tanks or other reserved storage volumes
A large tank with very little connected roof area may not provide the expected benefit. Likewise, a large catchment is of limited value if the tank is too small or has too little regular demand to create storage capacity.
The tank, catchment and connected uses should be practical for the site and coordinated with the roof drainage, hydraulic design and plans.
BASIX Reuse Storage and On-Site Detention Are Different
A council or stormwater design may require storage for on-site detention, retention or flood-management purposes. That storage is not automatically available for the household reuse commitment entered in BASIX.
Stormwater Control
Detention Volume
Temporarily stores runoff so discharge from the site can be controlled in accordance with drainage requirements.
Alternative Water
Reuse Volume
Stores water that remains available for recognised household, landscape or common-area uses.
Where one tank performs both functions, the volume nominated as available for BASIX reuse must be additional to any volume reserved for the required detention function.
Outdoor Water Use
How Pools and Spas Affect the Water Assessment
Pools and outdoor spas can increase estimated potable-water demand through initial filling, evaporation, splash-out and ongoing top-up.
The BASIX assessment can consider information such as:
- pool or spa volume
- whether the installation is indoor or outdoor
- the use of a pool or spa cover
- the amount of shading provided
- whether an individual rainwater tank supplies top-up water
- associated pump and heating information within the Energy assessment
A cover can reduce evaporation and help limit water loss when the pool or spa is not in use. Rainwater top-up may also support the water result where the system satisfies the applicable BASIX requirements.
Central Water Systems in Multi-Dwelling Developments
Larger residential developments can use central infrastructure to provide alternative water to several dwellings or common areas.
Central systems can include:
- shared rainwater tanks
- central stormwater tanks
- central on-site recycled-water systems
- reticulated alternative-water supplies
- water supplied to common landscaping
- water supplied to communal facilities
- relevant cooling-tower or fire-system water measures
The assessment must identify the source, available volume and nominated uses. Shared water should be allocated consistently between the dwellings and common areas without double counting.
Where a system also serves commercial areas, future stages or development outside the current application, the residential allocation may need to be established by the relevant hydraulic or services documentation.
Central recycled-water systems can also require separate authority approval, treatment, maintenance and operational arrangements beyond the BASIX calculation.
Assessment Response
How Can a Project Improve Its BASIX Water Result?
The appropriate response depends on which parts of the project are creating the highest potable-water demand and which alternatives are practical for the site.
Review fixture efficiency
Higher WELS-rated showerheads, toilets and taps can reduce internal potable-water demand without changing the building layout.
Coordinate landscape demand
The project can review the area of lawn, garden and low-water-use planting while maintaining the intended landscape outcome.
Increase practical alternative-water use
Rainwater or another recognised source may be connected to suitable recurring uses such as toilets, laundry or irrigation.
Review tank capacity and catchment together
A tank should be proportionate to the available roof collection and the uses that regularly draw water from it.
Reduce pool or spa water loss
Covers, shading and appropriate top-up systems can reduce the potable-water impact of outdoor water features.
Check the assessment information
Incorrect landscape areas, tank catchments, fixture ratings or connections can produce a result that does not represent the proposed design.
Which Water Commitments Should Appear on the Plans?
The final plans and specifications should communicate the water measures relied upon by the BASIX Certificate.
| Commitment | Relevant Documentation | Coordination Check |
|---|---|---|
| Fixture ratings | BASIX notes, schedules and specifications. | The selected products must meet the nominated WELS ratings and any committed flow ranges. |
| Rainwater tank | Site plan, roof plan, hydraulic plan and BASIX notes. | Tank capacity, catchment and connected uses should match the Certificate. |
| Landscaping | Site and landscape plans. | Lawn, garden and low-water-use areas should align with the BASIX inputs. |
| Pool or spa measures | Site plan, pool documentation and specifications. | Volume, cover, shading and top-up commitments should remain consistent. |
| Central systems | Hydraulic, civil and services documentation. | The supply, storage and allocation to dwellings or common areas should match the assessment. |
The architectural and landscape plans do not need to reproduce every calculation contained in BASIX. They should nevertheless show the physical measures necessary to understand and deliver the Certificate commitments.
Design Changes
What If the Water Design Changes After Certification?
A later design or product change should be reviewed where it alters an input or commitment relied upon by the water assessment.
Relevant changes can include:
- lower fixture ratings or higher shower flow rates
- a smaller rainwater tank
- a reduced roof catchment area
- removing toilet, laundry or irrigation connections
- changing the pool or spa volume
- removing a pool cover or shading commitment
- increasing lawn or garden area
- changing low-water-use planting
- revising common or central water systems
- changing dwelling numbers or development staging
The change may reduce the water score below the applicable target or cause the plans to conflict with the issued Certificate.
Where the assessment no longer represents the proposed work, the BASIX application and Certificate may need to be revised before the changed design is approved or constructed.
Common Misunderstandings About BASIX Water Efficiency
Every NSW project has the same water target
The target varies according to climate location and project circumstances.
Every BASIX project requires the same rainwater tank
Tank requirements are project-specific and depend on the selected water strategy, catchment, uses and target.
A larger tank always produces a better result
The result also depends on connected roof catchment, rainfall and regular water demand.
High-WELS fixtures remove the need to assess landscaping
Fixtures and landscaping are separate inputs. Extensive irrigated areas can still place pressure on the water result.
All stored water can be counted as BASIX reuse volume
Storage reserved for detention, firefighting or other requirements is not automatically available for BASIX household reuse.
Landscape commitments do not need to appear on the plans
Lawn, garden and nominated low-water-use areas should be coordinated with the development and landscape documentation.
A higher fixture rating can always replace another water commitment
The complete assessment must be recalculated. An improvement in one input may not compensate fully for removing another measure.
Passing BASIX guarantees low future water bills
The assessment uses standardised assumptions. Actual consumption continues to depend on occupancy, behaviour and system operation.
Frequently Asked Questions
BASIX Water Efficiency FAQs
What does the BASIX Water section assess?
It estimates the potable-water demand of a proposed residential development from its fixtures, landscaping, alternative water sources, pools, spas and relevant shared systems.
What is the BASIX water target?
The target is the minimum percentage reduction in potable-water demand that the project must achieve compared with the BASIX residential benchmark. The applicable percentage depends on the project location.
Does every BASIX project need a rainwater tank?
No. A tank is required where the project relies on rainwater to satisfy its water target or where it forms part of another applicable commitment. The required strategy is project-specific.
Which fixtures are assessed in BASIX?
BASIX generally assesses showerheads, toilets, kitchen taps and bathroom taps using their nominated WELS ratings and, where relevant, specific flow-rate ranges.
Do the installed fixtures need to match the BASIX Certificate?
Yes. The installed fixtures must satisfy the WELS ratings and any flow requirements relied upon by the BASIX assessment.
How does landscaping affect the water score?
BASIX considers the amount of lawn and garden, any areas of low-water-use planting and whether a recognised alternative water source supplies irrigation.
Can stormwater detention volume be counted as BASIX reuse storage?
No. The portion of a stormwater tank nominated for BASIX household reuse must be additional to any volume reserved for on-site detention or another regulatory purpose.
Do pools and spas affect the BASIX water result?
Yes. Pool or spa volume, covers, shading and any rainwater top-up arrangement can influence the project’s water commitments and calculated demand.
Can water commitments be changed after the Certificate is issued?
Changes should be reviewed where they affect fixture ratings, landscape areas, tank capacity, catchment, water connections, pool details or shared systems. A revised BASIX Certificate may be required.
Does a passing BASIX water result predict actual household consumption?
No. The result is a standardised regulatory calculation. Actual consumption also depends on occupancy, behaviour, rainfall, maintenance and how the water systems are operated.
Related Knowledge
Continue Exploring BASIX Water Requirements
Assessment note: BASIX water targets and available assessment inputs depend on the project location, dwelling type, landscape design, pools, common areas and proposed water infrastructure. The project-specific score and Certificate commitments should be checked against the current approval documentation.
For regulatory information, refer to the NSW Planning Portal BASIX Water guidance.
Last reviewed: July 2026.
BASIX Water Review
Coordinate the Water Strategy Before the Commitments Are Locked
Certified Energy can review the fixtures, landscaping, rainwater systems, pool requirements and shared water infrastructure and prepare coordinated BASIX documentation for the residential project.
Send Your Plans for Review →
