A Down-to-Earth Look at Costs, Savings, and Setup Before You Commit

Rain falls on your roof for free. The only question is whether you catch it or let it run down the drain.

At Tanks-A-Lot Ltd, most people who ask us about harvesting are really asking one thing: is it worth the money? For a well-chosen cistern tank, the answer is usually yes. Here’s how to judge it for your own property.

How does rainwater harvesting work?

There are four steps, and no magic involved:

1. Catch: rain runs off your roof into the gutters.
2. Filter: a mesh screen and first-flush diverter keep leaves and roof grit out.
3. Store: clean water flows into the tank.
4. Use: a pump or gravity feed sends it where you need it.

The tank is the heart of the system. Gutters and filters are easy to swap later, but the tank is the part you’ll live with for decades.

How much water could I collect?

Use this simple formula:

Roof area (m²) × annual rainfall (mm) × 0.8 = litres per year

The 0.8 allows for losses from splashing and overflow. Take a 100 m² roof in an area with 800 mm of yearly rain. That works out to 100 × 800 × 0.8 = 64,000 litres. It’s only an illustration, so check your local rainfall figures.

Rain also doesn’t arrive evenly. You need a tank big enough to carry you through the dry months, not just one storm.

Which type of tank suits me?

• Above ground: cheaper, easier to inspect and repair, but needs shade and floor space.
• Underground: keeps water cool and dark, which slows algae, but costs more to install.
• Polyethylene: light, affordable, and rust-resistant.
• Concrete: very durable, and well suited to large buried installations.

There’s no single winner. Small plots often go underground, while farms and workshops usually choose above-ground storage to keep costs down.

Where should I put it?

Pick ground that’s firm and level, with room for maintenance access. Keep it close to the roof catchment to cut down on piping.

Distance matters for safety, too. Stored water should sit well away from a septic holding tank or any other wastewater storage, and local rules set minimum gaps. Check them before you dig.

Is it really worth the investment?

The honest answer depends on three things: what you pay for water now, how much rain you get, and what you’ll use it for.

Stored rain suits gardens, toilet flushing, laundry, and cleaning. Those uses often make up a large share of household demand. For drinking, you’d need proper treatment and regular testing, and we wouldn’t recommend it without both.

Savings show up slowly on your bill and quickly in peace of mind. When supply is restricted or tanker prices jump, you have a reserve of your own.

What mistakes should I avoid?

• Buying too small because the bigger tank looked expensive
• Skipping the first-flush diverter
• Leaving the overflow uncovered and unpiped
• Forgetting lid security and vent screens
• Not planning where surplus water goes in heavy rain

How can Tanks-A-Lot Ltd help?

We size the tank to your roof, rainfall, and usage, then explain the trade-offs between materials in plain language. If a smaller tank does the job, we’ll say so.

We also stay reachable after installation, because questions always come up once the first rains arrive. Send us your roof size, location, and what you want to use the water for, and we’ll suggest a setup before you spend anything.

What’s the bottom line?

A good tank turns rain into a reserve you control. It’s one of the few property upgrades that keeps paying back quietly, year after year.

If your site also has a wastewater treatment plant, plan both systems together so pipes, access, and distances don’t clash. Talk to Tanks-A-Lot Ltd, and we’ll help you map out the full picture.