— Sarah. Every litre accounted for.
ArticlesCalculatorsSite PlannerShopStop wasting rain. If you're off-grid in Australia, you need this. Roof harvesting isn't rocket science—just bloody sensible.
By Sarah Chen · environmental engineer · water, waste and everything that flows downhill
“After my first Melbourne drought, I learned that a 5,000-litre tank is useless without a first-flush diverter, which saved me from three months of murky water.”
Stop wasting rain. If you're off-grid in Australia, you need this. Roof harvesting isn't rocket science—just bloody sensible. Here's how to do it right, no bullshit.
Simple maths. Roof area (m²) × annual rainfall (mm) × 0.9 = litres of water you can collect. Example:
But here's the catch: actual yield is less. Factor in evaporation, splash-out, and your roof type. Tile? Better than corrugated iron. Green roofs? Not for water collection. Just measure your roof footprint. If it's a shed, do it. If not, you're wasting rain.
First 10-20 litres of rain washes dust, bird shit, and pollen off your roof. That shit goes straight to drain, not your tank. Ignore this and you'll be filtering sand for weeks.
How it works: A pipe diverts the first flush into a small tank (usually 10-20L). Once that's full, water flows to your main tank. Simple. Cheap. Non-negotiable.
Buy a Brisbane Water or Rainwater Solutions first flush diverter. Costs $150-$300. Install it before your tank. Done.
Size based on your needs. Not some "average" number. If you've got 2 people, 10,000L tank is bare minimum. 15,000L for a family. 20,000L if you're serious about off-grid.
Rule of thumb: 100L per person per day. So 3 people = 300L/day. Multiply by 30 days = 9,000L. Add 50% buffer. Total: 13,500L. Round up to 15,000L.
Big tanks are cheaper per litre. A 15,000L tank costs ~$2,200. A 20,000L? ~$2,800. Don't skimp. You'll regret it when you're rationing showers during a drought.
Australian suppliers (2023 pricing):
Tip: Buy a 15kL tank now. Add a second later. Cheaper than buying a tank too small and replacing it.
Don't wait for the drought to hit. Your roof is a water factory. Install a first flush. Size your tank right. Measure your roof. Buy the gear. It's not hard. It's not expensive. It's just bloody necessary.
Ignore this and you'll be buying bottled water from the pub while the rain falls. Not a good look for an off-grid Aussie.
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: Rainwater Harvesting Epic DIY Off-Grid Rain Roof Build- Material Gathering · Our Self-Reliant Life