6 Things You Need to Know About Cleaning Rainwater Tanks


A house with two rainwater tanks being used to supply clean drinking and shower water.

Showering and drinking pure rainwater sounds heavenly, but the tank is usually anything but heaven. Rainwater is collected and stored before it can be used and that’s when the impurities and bacteria can build up in the tank without you knowing.

Why Rainwater Tanks Need Cleaning

Rainwater can be contaminated with smoke and smog particles as it lands on a surface. When the rain hits the roof of a house, it can collect dirt, dust, bird droppings and even possum faeces. Old leaves and dirt in the gutters can also be washed into the tank. Even if you use a first flush diverter, contaminants can still make their way into the tank. There’s also the risk of mosquitoes and other insects breeding in the tank. However, the smallest contaminants in a rainwater tank can be the nastiest. Microorganisms such as bacteria can cause gastrointestinal illnesses including vomiting and diarrhoea.

Water tank cleaning sounds like a fairly simple task once you’re in the tank, but there are few tips you should be aware of.  

#1 Clean Your Tank When the Water Level is Low

The end of the dry season is the best time to clean the tank, when the water level is fairly low and you won’t waste too much when the tank is emptied. However, you don’t want to squeeze as much water as possible from your tank if it hasn’t been cleaned in years. You might be horrified that you were drinking water that’s close to the sludge at the bottom of the tank.

#2 Turn Off the Power

Safety first. Don’t forget to turn the power off and pull the plug out of the tank. Double check that there’s no electricity running to the tank before opening the lid.

#3 Consider Using a Professional Tank Cleaner

Tank cleaning is not only a nasty job (think of what years of rotting organic matter looks like), but it can also be a deadly job. In rural New South Wales in 2017, three people died from what was suspected to be a build-up of carbon monoxide gas in the bottom of an empty concrete tank while it was being cleaned using a petrol-powered water pump.

A professional tank cleaner has the right equipment and experience to ensure everyone stays safe during the cleaning process.

#4 Cleaning Out the Sludge

Organic material on the bottom of the tank that has formed a sludge can be cleaned without removing the water through a tube inserted through the tank’s inlet. If you’re emptying the tank and cleaning the tank’s floor, be aware of the slip and fall risks. Work alongside another person or have someone check on you regularly.

#5 Use a High Quality Water Treatment Solution

To treat rainwater or not? Rainwater treatment has been a hotly contested debate for years. If you’re using rainwater for drinking and cooking, the safest option is to boil or treat the water before consumption. Chlorine has been used for many years to kill bacteria in water sources. However, many people don’t like the smell or taste of chlorinated water. Using chlorine for water purification has a limited life and needs regular monitoring particularly when the weather is warm.

Superior Water Tank Treatment

Sanosil uses hydrogen peroxide and silver to effectively treat water with no odour or taste. The product is far more stable than chlorine, so it offers long-term residual disinfection compared to chlorine. When hydrogen peroxide breaks down, its by-products are oxygen and water, so it’s better for the environment than chlorine. The other by-product risk of chlorine is trihalomethanes, which occur when chlorine or bromine reacts with organic material in the water. This risk is also eliminated by using Sanosil.

#6 Maintenance After Cleaning

Once your tank is clean and the water is treated, spend a little time keeping the tank clean by:

  • Covering the inlet and overflow with mesh to keep insects and animals out.

  • Protect the water with a cover to prevent any light getting in which encourages bacteria and algae growth.

  • Make sure gutters drain to avoid corrosion and metal contaminants in the water.

  • Clean the leaf trap and gutters regularly.

  • Fit a diverter (also known as a roof washer) so the first flow of water is diverted away from the catchment system to wash the roof of sediment and contaminants that have settled since the last rains.

  • Use a diverter after a bushfire as ash on the roof may contain arsenic and other heavy metals.

  • Inspect the tank regularly.

If you would like more information about how Sanosil can purify your rainwater tank so it’s safe to drink, call 1300 29 32 32 or contact us online.