Do I need a rainwater tank?
Not always. The Planning (Residential Zones) Technical Specifications 2026 require new single dwellings, secondary residences, and most extensions or alterations to meet one of three water efficiency options:
- Option A – Rainwater tank: The required tank size depends on the block size:
- Compact blocks: No rainwater tank is required, but high-efficiency (minimum 3-star WELS) plumbing fixtures must be installed.
- Mid-sized blocks: Minimum 2,000 L rainwater tank.
- Large blocks up to 800 m²: Minimum 4,000 L rainwater tank.
- Large blocks 800 m² or greater: Minimum 5,000 L rainwater tank.
The tank must collect water from part of the roof and be connected to at least a toilet, laundry cold water, and external taps.
- Option B – Greywater system: Install a Class A treated greywater system connected to toilets, laundry cold water, and external taps.
- Option C – Water efficiency: Demonstrate that the development will reduce mains water use by at least 40% compared with an equivalent 2003 development, without relying on landscaping measures.
So, you do not always need a rainwater tank, as long as your development meets one of the other approved water efficiency options.
Reference: Planning (Residential Zones) Technical Specifications 2026 (NI2026-303), Assessment Outcome 19.5- Planning (Residential Zones) Technical Specifications 2026
Short Answer
Not always. New single dwellings, secondary residences, and most extensions or alterations must meet one of three water efficiency options. For many developments, this means installing a rainwater tank, but you can also choose an approved greywater system or demonstrate a 40% reduction in mains water use.
Detailed Explanation
Not always.
New single dwellings, secondary residences, and most extensions or renovations must meet one of three water-saving options under the Planning (Residential Zones) Technical Specifications 2026.
The most common option is to install a rainwater tank, with the required size depending on your block:
- Compact blocks: No rainwater tank is required, but you must install water-efficient (minimum 3-star WELS) plumbing fixtures.
- Mid-sized blocks: At least a 2,000-litre rainwater tank.
- Large blocks up to 800 m²: At least a 4,000-litre rainwater tank.
- Large blocks 800 m² or larger: At least a 5,000-litre rainwater tank.
The rainwater tank must collect water from part of the roof and be connected to at least one toilet, the laundry cold-water supply, and external taps.
Instead of a rainwater tank, you can choose:
- a Class A treated greywater system that reuses water from bathrooms and the laundry for toilets, laundry cold water, and outdoor taps; or
- another approved solution that shows the home will use at least 40% less mains water than a similar home built to 2003 standards.
In summary, you do not always need a rainwater tank, provided your development meets one of the other approved water efficiency options
No minimum block size does not remove the need for planning assessment.
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