BASIX Water Efficiency NSW 2026: Rainwater Tanks, WELS Fixtures & Landscape Compliance Guide
What Is the BASIX Water Section?
The BASIX Water section requires new residential developments in NSW to reduce potable water consumption by up to 40% compared to a pre-BASIX benchmark of 90,340 litres per person per year (approximately 247 litres per person per day). Introduced under the State Environmental Planning Policy (Sustainable Buildings) 2022, the water targets vary by climate zone and apply to all new homes, renovations over $50,000, and pools or spas over 40,000 litres. The 40% reduction standard covers 90% of new residential development and 98% of high-growth areas across NSW.
How Does BASIX Assess Water Efficiency?
BASIX estimates the potable-water demand of a proposed development by evaluating six assessment areas: fixtures (showerheads, toilets, taps), landscaping (lawn, garden, low-water-use planting), alternative water sources (rainwater, stormwater, greywater), pools and spas, common areas (for multi-dwelling projects), and central water systems. The assessment compares the calculated reduction against the applicable target for the project's climate zone. Each measure selected becomes a binding commitment that must match the final construction documentation, not just a design-stage estimate.
BASIX Water Target by Climate Zone
| Climate Zone | Typical Location | Water Reduction Target |
|---|---|---|
| Zone 4-5 | Sydney Metro, coastal NSW | 40% |
| Zone 6 | Blue Mountains, Southern Highlands | 35-40% |
| Zone 7 | Canberra region, Alpine NSW | 30-35% |
| Zone 8-9 | Western plains, semi-arid | 20-30% |
| Zone 10-11 | Northern coastal, subtropical | 0-20% |
Source: NSW Planning Portal Water Use Maps, SEPP (Sustainable Buildings) 2022.
Do You Need a Rainwater Tank for BASIX Compliance?
No universal rule requires every BASIX project to install a rainwater tank. A tank becomes necessary when the assessment relies on rainwater to achieve the applicable water target. Other projects may meet their target through a combination of high-WELS fixtures, low-water landscaping, or reticulated recycled water. However, in practice, most new homes in Sydney and coastal NSW (climate zones 4-5) require a rainwater tank because the 40% reduction target is difficult to achieve through fixtures alone.
Rainwater Tank Sizing Guide
| Dwelling Type | Typical Tank Size | Connected Roof Area | Supplied Uses |
|---|---|---|---|
| 2-bed apartment | 1,000-2,000L | 50-80m² | Toilet flushing |
| 3-bed house (Sydney) | 2,000-4,000L | 80-150m² | Toilets, laundry, garden |
| 4-bed house | 4,000-5,000L | 150-200m² | Toilets, laundry, irrigation |
| Townhouse (multi-dwelling) | 2,000-3,000L per unit | 60-100m² per unit | Toilets, garden |
The key principle is that tank capacity, roof catchment area, and connected end uses must work together. A large tank with minimal roof catchment will underperform. A large catchment with a tiny tank cannot store enough water during rainfall events. The tank should be proportionate to the available collection area and the regular water demand from connected fixtures.
How WELS Fixtures Contribute to Your BASIX Water Score
The Water Efficiency Labelling and Standards (WELS) scheme rates fixtures from zero to six stars. BASIX uses the nominated WELS ratings of showerheads, toilets, kitchen taps, and bathroom taps to estimate indoor water demand. More efficient fixtures reduce the estimated demand on potable water supplies. Showerheads and taps that use less hot water also reduce energy required for water heating, which improves the BASIX Energy score simultaneously.
Recommended WELS Ratings for BASIX Compliance
| Fixture | Minimum WELS Rating | Flow Rate | BASIX Impact |
|---|---|---|---|
| Showerheads | 3-star (minimum) | 7.5-9 L/min | Highest impact on indoor demand |
| Toilets | 4-star | 3.5-4.5 L/flush | Significant flushing reduction |
| Kitchen taps | 3-star | 6-7.5 L/min | Moderate impact |
| Bathroom taps | 3-star | 6-7.5 L/min | Moderate impact |
| Dishwasher (apartments) | 3-star+ | As rated | Appliance credit for units |
From the May 2026 tool upgrade, showerheads consuming between 4.5 and 6 litres per minute now appear as 5 stars in the BASIX tool, providing greater recognition for ultra-efficient fixtures. This creates an additional pathway to compliance for homes with limited roof catchment or challenging site constraints.
How Landscaping Affects Your BASIX Water Score
Outdoor water demand can form a significant part of the BASIX calculation, particularly for homes with large gardens or lawns. The assessment records the proposed areas of lawn, garden, and any areas nominated for low-water-use plant species. Reducing irrigated area or selecting drought-tolerant native planting reduces estimated potable-water demand.
For multi-dwelling developments such as townhouses and apartments, private and common landscape areas must be separated in the assessment. Private courtyards, gardens, and lawns allocated to individual dwellings should not be entered as common property, even where the development is proposed for strata subdivision.
Common Landscape Compliance Issues
In our experience at giantA, the most frequent landscape-related compliance failures occur when homeowners change their landscaping after BASIX certification. Converting a nominated low-water-use native garden to a conventional lawn, or expanding the irrigated area beyond what was assessed, can invalidate the BASIX certificate. These changes should trigger a BASIX review before construction proceeds, because the revised water score may fall below the applicable target.
Which Alternative Water Sources Does BASIX Recognise?
BASIX recognises several alternative water sources that can reduce potable-water demand by supplying suitable non-drinking uses within the development.
| Water Source | Description | BASIX Considerations |
|---|---|---|
| Rainwater | Collected from non-trafficable roof areas | Assessed by tank volume, catchment area, connected uses |
| Stormwater | Runoff from trafficable or site surfaces | Treatment requirements apply; reuse volume separate from detention |
| Greywater | Wastewater from bathroom and laundry sources | Uses depend on diversion vs treatment; separate approvals needed |
| Reticulated recycled water | Non-potable supply via separate reticulation | Must align with serving authority specifications |
| Private dam | Stored surface water (single dwellings only) | Eligible for single-dwelling developments only |
Groundwater, river water, and ordinary on-site sewage-management systems are not automatically recognised as BASIX alternative water sources.
BASIX Reuse Storage vs On-Site Detention
A critical distinction that catches many projects off guard: BASIX reuse storage and on-site detention (OSD) volumes are different functions. Where one tank performs both roles, the volume nominated as available for BASIX reuse must be additional to any volume reserved for the required detention function. Council or stormwater designs that require OSD cannot have that same volume double-counted for BASIX household reuse. This is one of the most common errors we encounter during pre-DA reviews at giantA, particularly in Parramatta and Blacktown council areas where OSD requirements are stringent.
How Pools and Spas Affect BASIX Water Compliance
Pools and outdoor spas increase estimated potable-water demand through initial filling, evaporation, splash-out, and ongoing top-up. BASIX assesses pool or spa volume, whether the installation is indoor or outdoor, use of a cover, shading provided, and whether a rainwater tank supplies top-up water. A pool cover can significantly reduce evaporation and help limit water loss. The May 2026 BASIX tool upgrade expanded the glazing options for alterations and additions with low solar heat gain coefficient values, providing more flexibility for indoor pool enclosures.
What Has Changed in the May 2026 BASIX Tool Upgrade?
The 1 May 2026 tool upgrade introduced several changes relevant to the water section:
1. Data retention on method switching — When users switch between Simulation and DIY thermal methods, water data is now retained, eliminating the need to re-enter all inputs 2. Declaration requirement — All users must now declare that entered information is accurate before generating a BASIX certificate 3. Showerhead ratings update — Showerheads consuming 4.5 to 6 litres per minute now display as 5 stars, recognising ultra-efficient fixtures 4. Expanded glazing options — For alterations and additions, low solar heat gain coefficient glazing options are now available 5. Multi-dwelling capacity — BASIX certificates can now include up to 1,000 dwellings, accommodating large-scale apartment developments 6. Green Square Town Centre — Homes in postcode 2015 can select the Green Square Town Centre reticulated alternative water supply option 7. Ventilation changes — Bathroom, kitchen, and laundry ventilation systems no longer allow directing exhaust into the roof space
Stakeholder Implications
For Homeowners
If you are planning a renovation over $50,000 or building a new home, the BASIX water section will determine your fixture selections, rainwater tank requirements, and landscape design. Plan your water strategy early, before finalising architectural drawings. Changing fixtures or landscaping after BASIX certification can invalidate your certificate and require a revised assessment. The cost of a rainwater tank installation (typically $2,000-$5,000 for a 2,000-4,000L system) should be factored into your construction budget from the outset.
For Developers
Multi-dwelling developers should coordinate private and common landscape areas before the BASIX assessment. The May 2026 upgrade allows up to 1,000 dwellings on a single certificate, streamlining large-scale projects. However, central water systems require separate hydraulic documentation and potentially separate authority approvals beyond the BASIX calculation. Early engagement with a BASIX assessor during the design phase prevents costly redesigns at the DA stage.
For Builders and Certifiers
The installed fixtures must satisfy the WELS ratings and flow commitments on the BASIX certificate. Builders should verify that all showerheads, toilets, and taps match the nominated specifications before installation. The new declaration requirement (May 2026) places additional responsibility on the person completing the BASIX assessment to confirm accuracy, making pre-construction verification even more critical.
Real Project Examples
In a recent giantA project in Merrylands (12-unit townhouse development, Cumberland Council), the initial BASIX water assessment fell short of the 40% target by 4 percentage points. The issue was that the landscape plan nominated 180m² of irrigated lawn across private courtyards, but the BASIX assessment had only accounted for 120m². By revising the landscape plan to include 60m² of low-water-use native planting (grevillea, callistemon, and lomandra species), we achieved a 42% reduction and a compliant certificate. The cost of native planting was approximately $3,200 — far less than the $12,000 rainwater tank upgrade that would have been required as an alternative.
For a single-dwelling project in Blacktown, a client wanted to avoid installing a rainwater tank due to site constraints. By specifying 5-star WELS showerheads (5.5 L/min), 4-star toilets, and 3-star taps throughout, combined with a 70% low-water-use garden, we achieved the 40% target without any tank. The fixture upgrade cost approximately $450 above standard fittings, but saved $3,200 on tank installation and associated plumbing.
FAQ: BASIX Water Efficiency in NSW
What is the BASIX water benchmark?
The BASIX water benchmark is 90,340 litres per person per year, equivalent to approximately 247 litres per person per day. This represents the average potable water consumption of a pre-BASIX home in NSW. The BASIX water target requires your project to reduce consumption by 0% to 40% from this benchmark, depending on your climate zone.
Do all NSW homes need a rainwater tank for BASIX?
No, there is no universal requirement for a rainwater tank. A tank is only required where the project relies on rainwater to achieve its water target. Some projects can meet the target through high-WELS fixtures and low-water landscaping alone, particularly in climate zones with lower reduction targets.
What WELS rating do showerheads need for BASIX?
BASIX requires a minimum 3-star WELS rating for showerheads (7.5-9 L/min flow rate). Specifying 4-star or 5-star showerheads (4.5-6 L/min) provides additional credit toward the water target. The May 2026 update means showerheads using 4.5-6 L/min now display as 5 stars in the BASIX tool.
Can I change my landscaping after BASIX certification?
Changing landscaping after certification can invalidate the BASIX certificate. Converting low-water-use planting to conventional lawn, or expanding irrigated areas beyond what was assessed, reduces the water score and may require a revised certificate. Always review BASIX implications before making landscape changes.
Is stormwater detention volume the same as BASIX reuse volume?
No, they are separate functions. On-site detention (OSD) volume temporarily stores runoff for controlled discharge. BASIX reuse volume stores water for household use. Where one tank serves both, the BASIX reuse volume must be additional to the OSD reserve volume.
How do pools and spas affect BASIX water compliance?
Pools and spas increase potable-water demand through filling, evaporation, and top-up. BASIX considers volume, indoor/outdoor installation, covers, shading, and rainwater top-up. Pool covers significantly reduce evaporation and help maintain compliance.
What happens if my water fixtures do not match the BASIX certificate?
Installed fixtures must satisfy the WELS ratings and flow ranges nominated on the certificate. Non-compliant fixtures create a discrepancy between the certificate and the actual construction, which can be flagged during certification inspections and may require replacement of the installed products.
Does the May 2026 BASIX tool upgrade change water targets?
No, the May 2026 upgrade does not change the water reduction targets themselves. It improves the tool's functionality, expands fixture and glazing options, requires accuracy declarations, and allows larger multi-dwelling certificates. The underlying SEPP (Sustainable Buildings) 2022 targets remain unchanged.
Author: Franz Phan, Senior Planning Consultant, giantA Pty Ltd. 15+ years experience in NSW residential development, BASIX compliance, and building approvals.
Sources: NSW Planning Portal (planningportal.nsw.gov.au), SEPP (Sustainable Buildings) 2022, BASIX Tool Upgrade Summary 1 May 2026, NCC 2022.
For BASIX water compliance assistance on your NSW project, contact giantA at 1300 655 655 or visit [gianta.com.au](https://gianta.com.au).