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How to Clean Your Rainwater Tank for Optimal Water Quality

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Rainwater tanks offer a sustainable water source and contribute significantly to reducing mains water dependence. However, the benefits of a rainwater tank are closely tied to its maintenance, particularly the cleanliness of the water it stores. Without proper cleaning, the water in these tanks can become a breeding ground for bacteria, algae, and other contaminants, ultimately defeating the purpose of having a clean, independent water supply.

Understanding how to clean your rainwater tank is essential for ensuring your filtered rainwater remains safe for use, whether for irrigation, laundry, or even potable water after proper treatment.

In this blog, we’ll delve into a comprehensive process on how to clean your rainwater tank. We’ll cover everything from understanding the preparation for cleaning to the actual cleaning process and post-cleaning maintenance to guarantee optimal water quality.

Understanding Your Rainwater Tank

Types of Rainwater Tanks

Rainwater tanks come in various shapes, sizes, and materials, each catering to different needs and preferences. The most common materials used for rainwater tanks are polyethylene (plastic), fibreglass, concrete, and metal (such as galvanized steel or stainless steel).

Polyethylene Tanks

Polyethylene tanks are popular due to their affordability and versatility. They are lightweight, resistant to corrosion, and suitable for both above and underground installation. However, they can be susceptible to UV damage if not properly treated or shielded from the sun.

Fibreglass Tanks

Water tanks made from fibreglass are known for their durability and resistance to chemicals and corrosion. They are slightly more expensive but are an excellent choice for long-term use.

Concrete Tanks

Often used for underground storage, concrete tanks are valued for their longevity and ability to maintain a stable water temperature. They are, however, more expensive and require a solid foundation.

Metal Tanks

Metal rainwater tanks, particularly those made of stainless steel, are highly durable and resistant to corrosion. Galvanised steel tanks are more affordable but can be prone to rust over time, especially if they are not properly lined or treated.

How Contamination Occurs

Contamination in rainwater tanks can occur in several ways. The most common source is debris from roofs, such as leaves, dirt, and animal droppings, which are washed into the tank by rainwater. These materials can decompose in the tank, affecting the water quality.

Another source of contamination is algae growth, which can occur in tanks that are exposed to sunlight. Algae can not only discolour the water but also affect its taste and smell.

Microbial contamination from birds, animals, and insects can also pose health risks. Moreover, if the tank is not adequately sealed, small animals and insects can enter the tank, further contaminating the water.

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Pre-Cleaning Preparation

Before going into the cleaning process, it’s essential to prepare adequately to ensure safety and efficiency. This preparation involves gathering the right tools, taking safety precautions, and draining your tank.


Before starting, equip yourself with the necessary safety gear. This includes gloves, non-slip boots, protective eyewear, and a face mask or respirator, especially if you’re using chemical disinfectants.

Working in a well-ventilated area is crucial to avoid inhaling harmful fumes. Also, if you’re working at height (on top of an above-ground tank, for instance), ensure you have a stable ladder and someone to assist you if needed.

Tools and Materials

Gather all the tools and materials you’ll need for cleaning. This typically includes:

  • A submersible pump or siphon for draining the tank.
  • A high-pressure hose or a bucket and sponge for scrubbing.
  • A scraper or soft-bristled brush to remove algae and sediment.
  • Safe, tank-appropriate disinfectants (like chlorine bleach, ensuring it’s safe for use in rainwater tanks).
  • A clean cloth or mop for drying out the tank after cleaning.
Draining Your Tank Water

Before cleaning, you need to drain the tank. This can be done using a submersible pump or by simply opening the tank’s valve to let the water flow out. Ensure the water is directed away from the house and garden beds to avoid flooding.

It’s important to leave a small amount of water at the bottom of the tank to help loosen the sludge during cleaning.

The Rainwater Tank Cleaning Process

Cleaning your water tank is crucial in maintaining water quality. This process involves several stages, which include:

Physical Removal of Debris

Start by removing the sludge and debris that have settled at the bottom of the tank. Use a scoop, shovel, or similar tool for this task. Be gentle to avoid damaging the tank’s interior, especially if it’s made of a softer material like plastic or fibreglass. Dispose of the sludge responsibly, considering that it may contain contaminants.

Scrubbing and Rinsing

Once the debris is out, scrub the interior surfaces of the tank. A long-handled brush or sponge works well for this purpose.

Pay special attention to corners and joints where algae and bacteria tend to accumulate. After scrubbing, rinse the tank thoroughly with clean water.

This step might need to be repeated several times to ensure all the cleaning agents and residual dirt are washed away.

Disinfecting the Tank

Disinfecting the tank is crucial to kill any remaining bacteria or microorganisms. Common disinfectants include chlorine bleach or other tank-safe products. When using bleach, follow the manufacturer’s guidelines to ensure the correct concentration.

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Post-Cleaning Procedures

Refilling the Tank

Once the tank is clean and dry, it’s time to refill it. If possible, wait for a rainfall event to allow the tank to fill naturally. This not only ensures fresh rainwater but also helps to rinse any residual cleaning agents.

Water Quality Testing

After the tank is refilled, testing the water quality is crucial, especially if the water is used for household purposes. You can use home testing kits for basic water quality parameters like pH, chlorine levels, and hardness.

The Complete Home Filtration Rainwater Tank Filtration System

Cleaning your rainwater tank can be tedious, even at the best of times. As a response to this, we’ve developed a world-class UV disinfection system that eradicates any harmful bacteria and pathogens that come into your rainwater supply.

With ultraviolet sterilisation technology, it provides you with a chemical-free and cost-effective solution to protect your home from harmful microorganisms. In addition, it removes the need for the manual labour of cleaning your rainwater tank regularly.

Final Words

If you’re looking to optimise the output of your rainwater tank and enjoy high-quality drinking water, rely on us at Complete Home Filtration. Our world-leading rainwater tank filtration system allows you to enjoy fresh drinking water year-round. Contact us today to learn more about our range of products and begin your journey to cleaner and safer stored rainwater.