By Sarah Chen · environmental engineer · water, waste and everything that flows downhill
“After losing three-quarters of my stored water to algae in my first off-grid tank, I learned that shade is non-negotiable for Australian rainwater.”
— Sarah. Every litre accounted for.
ArticlesCalculatorsSite PlannerShopForget the marketing fluff. If you're off-grid in Australia, rainwater harvesting isn't optional—it's survival. Here's how to do it right, with Aussie prices and standards.
By Sarah Chen · environmental engineer · water, waste and everything that flows downhill
“After losing three-quarters of my stored water to algae in my first off-grid tank, I learned that shade is non-negotiable for Australian rainwater.”
Forget the marketing fluff. If you're off-grid in Australia, rainwater harvesting isn't optional—it's survival. Here's how to do it right, with Aussie prices and standards.
Simple math. No apps needed. Formula: Roof Area (m²) × Rainfall (mm) × 0.001 = Litres
Example: Your 100m² roof gets 100mm rain → 100 × 100 × 0.001 = 10,000L. That's 10,000 litres from one decent storm.
Real Aussie note: Use Bureau of Meteorology data for your postcode. Sydney averages 1,200mm/year. Outback? 250mm. Plan for droughts.
First 10-20L of rain washes roof dust, bird poo, and dead bugs. You don't want that in your tank. A first flush diverter is non-negotiable.
How it works: Diverts first 10-20L to waste. Then clean water flows to tank. AS/NZS 3500:2018 requires it for potable systems.
Aussie supplier: Aqua-Logic First Flush Diverter (AS/NZS certified) - $45 at Amazon Australia
Rule of thumb: 1,000L per person per day for basic needs (cooking, washing). But Australia's dry—plan for 3 months without rain.
Example: 4 people × 1,000L/day × 90 days = 360,000L. That's a 40,000L tank (since you'll use it over time).
| Tank Type | Pros | Cons | Aussie Price (AUD) | Supplier |
|---|---|---|---|---|
| Polyethylene (PE) | Lightweight, UV-resistant, easy install | Can crack if hit hard (rare) | $500 - $5,000 | WaterTank Australia |
| Fibreglass | Long-lasting (20+ years), no UV issues | Heavy, expensive, hard to move | $2,000 - $10,000 | Fibreglass Tanks Australia |
| Concrete | Ultra-durable, huge capacity | Costly, requires heavy machinery | $5,000+ | Local concrete suppliers |
AS/NZS 3500:2018 is your bible. It covers tank materials, installation, and safety. Ignore it and your system fails.
Filter before the tank: Mesh screen (A$25 at Amazon Australia) stops leaves and bugs.
Size your pump: 12V pumps (like the Sunway 12V) cost $200-$400. Match to your tank size.
Don't overcomplicate: A 5,000L tank + first flush + basic filter = $1,000. That's your baseline. Add more later.
Rainwater harvesting in Australia isn't about fancy tech. It's about knowing your roof area, installing a first flush, and sizing a tank that won't leave you dry when the dam's empty. Do it right, and you'll never pay for town water again. Get the basics sorted, then upgrade. No more excuses.
While many off-grid projects are achievable as DIY, certain situations require licensed professionals:
Always check local regulations and obtain necessary permits before commencing work.
Worth a watch: The Self Watering garden: How to Create a Passive Rainwater System with Dr Cally Brennan · Canberra Environment Centre