How to setup a rainwater tank?

Setting up a rainwater tank is a straightforward project that most DIY homeowners can complete in a weekend. Whether you are installing a small water butt or a large above-ground storage tank, the principles are the same.

Step 1: Choose the Right Location

The ideal location is as close as possible to a downpipe that collects water from your roof. The ground should be level, well-drained, and capable of supporting the weight of a full tank — water weighs approximately one kilogram per litre, so a 1000-litre tank weighs a tonne when full. Avoid placing the tank directly against building walls. Consider access for maintenance and also think about aesthetics.

Step 2: Prepare a Firm, Level Base

A stable base is essential. For small water butts up to 300 litres, a purpose-built stand or a paved slab is adequate. For larger tanks, excavate a shallow area, lay a hardcore base of compacted rubble or gravel to a depth of 100–150 mm, then top with paving slabs or a concrete pad. Ensure the base is perfectly level using a spirit level. Most tanks benefit from being raised slightly above ground level for convenient tap access.

Step 3: Install the Downpipe Diverter

A rainwater diverter fits into your existing downpipe and diverts a portion of the flow into the tank. Cut a section out of your downpipe with a hacksaw and fit the diverter body in its place. Most diverters come with rubber connectors or compression fittings that create a watertight seal. Connect the outlet hose from the diverter to the inlet of your tank, ensuring the hose runs downhill for free flow.

Step 4: Fit the Overflow

Every rainwater tank needs an overflow outlet near the top to handle excess water. Direct this away from your property's foundations. Many systems direct the overflow back into the original downpipe downstream of the diverter, so excess water continues to the drain. Fit a mesh or grille at the overflow outlet if recommended by the manufacturer.

Step 5: Fit the Outlet and Optional Pump

For gravity-fed watering, install a tap at the bottom of the tank. For pressurised water, install a pump — submersible pumps sit inside the tank and are quiet, while external pumps are easier to service. Fit a non-return valve on the outlet and an isolation valve for servicing. For indoor supply, include a float switch or level sensor to protect the pump from running dry.

Step 6: Test and Commission

Once everything is connected, test the system thoroughly. Wait for rain or run water from a hose into the gutters to simulate rainfall. Check that water flows freely from the downpipe diverter into the tank, that the overflow operates correctly, and that there are no leaks at any connection. Test the tap or pump to confirm adequate flow. Inspect the tank lid to ensure it seals properly and keeps out debris, insects, and animals. Make a note of your tank capacity and check how quickly it fills — this will help you understand your system's performance and plan your water usage. With the system commissioned, you can start using your harvested rainwater immediately for garden watering, car washing, or any other outdoor use.

Ongoing Maintenance Tips

Once your rainwater tank is set up, regular maintenance keeps it functioning well. Clean gutters at least twice a year, particularly during autumn when leaf fall is heaviest. Inspect and clean the downpipe diverter filter every few months. Check the tank lid seal annually and replace if perished. If you have a pump, service it according to the manufacturer's schedule — typically an annual check of seals, impellers, and electrical connections. Draining the tank completely every two to three years for a thorough clean prevents sediment buildup and maintains water quality. With proper setup and regular care, your rainwater tank will provide free, soft water for many years.