clean you water tank

How to Clean Your Rainwater Tank

Lots of people think that tank water is drinkable – after all, what could be purer than rainwater from the sky?

The truth is that while rainwater itself is free of chemicals and other additives that can be found in our drinking water, you do need to clean your rainwater tank regularly to ensure high-quality water.

Tank water can gather a variety of impurities both on its way down from the clouds and within your rainwater tank. For example, smog and smoke haze particles can attach to droplets of water as they fall through the sky. Within your rainwater tank, bacteria, leaves and other debris may contaminate your water. 

Mosquitos may try to breed within your tank water too – potentially causing your tank to become a haven for disease. 

The good news is that if you take the time to clean your tank each year, you can prolong its life and keep your water clean and healthy. It’s relatively simple to clean your rainwater tank, and maintain clean water throughout the year.

Step 1 – Wait until after summer as water will be lowest.

It’s recommended that you wait until the end of summer to clean your rainwater tank. That’s because the water level will be at its lowest at that time. 

First, turn the power off if you have an electric pump, and pull the plug completely out of its socket to be sure there is no electricity flow remaining. 

Step 2 – Drain your tank

Now it’s time to drain your tank. Use the remaining water around your garden, top up your pool, or fill your pond. Then run some fresh water from your garden hose through the tank inlet to flush out any remaining dirty water. Keep doing this until the water runs clear – you may need to increase water pressure to give the outlet a really good rinse. 

Step 3 – Remove the sludge

Here comes the ‘fun’ part… removing sludge. Rotting leaves and other organic debris can make the bottom of your tank pretty slimy. 

It’s important to note that working inside a tank can be dangerous, so consider using a professional tank cleaner if you can. 

To stop sludge building up in the first place, you may want to use a first flush diverter (or roof washer) which diverts the flow of water away from your catchment system, or leaf strainers which stop organic matter from entering your tank. 

If you’re already using these, don’t forget to clean them out as well – if they’re clogged they can’t do their job. 

Step 4  – Connect power and fill the tank again

Now you have a clean tank, you can reconnect your power and set up your tank again. Fill the tank to cover the pump opening, and flush the taps in your property to bring through clean water from the tank.

It’s a good idea at this stage to clean your gutters as well – the cleaner your roof, the less likely your tank will fill with debris and insects that rainwater washes down into the tank. Ensure that your strainer screens are still in good enough condition to prevent insects, leafy debris and dead animals from falling into your tank. 

You should be cleaning your strainers around 3 times a year. Also it’s wise to check them after big storms and other significant environmental events (such as a dust storm or bushfire) to make sure they haven’t been damaged, and are unclogged.

Consider using UV filters for drinking water

If you use your rainwater tank to supply drinking water, you may want to consider using UV air and water filters to kill pathogens and help maintain a clean water supply. Used along with carbon filters, UV water filtration systems are the best line of defence against bacteria and viruses. 

UV energy destroys microorganisms that may cause illness by attacking them at their genetic core and eliminating their ability to reproduce. 


ASC Water Tanks have been supplying Australian homes with rainwater tanks since 2007. We sell top-grade Australian Made water tanks to support our economy and to deliver a superior product to our customers.

To discuss how to set up a rainwater harvesting system in your home, contact us here or give us a call on 1300 229 606.

1 thought on “How to Clean Your Rainwater Tank”

  1. I didn’t know that you have to drain your tank to remove the sludge buildup and clean out the leaf strainers. My husband and I would like to get water tanks installed on the property to help us lower our utility bills. We’ll start looking for a rainwater tank from a service that also offers maintenance services.

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