7 Ways to Prevent Algae in Rain Barrels

Co-authored by Scott Johnson and Hannah Madden

Last Updated: June 18, 2025 Fact Checked

Rain barrels are a great way to conserve water—but the humid nature of rain barrels also creates the perfect environment for algae. While a little bit of algae in your rain barrels is fine, too much algae has the potential to clog your overflow valve and your hose. Fortunately, with the right cleaning methods and storage techniques, you can prevent algae in your rain barrels.

1

Keep the barrels out of direct sunlight.

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Algae thrives in sunlight, so keep your barrels in the shade. Algae, just like plants, needs sunlight to grow.^{[1]
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Scott Johnson
Landscape & Design Consultant

Expert Interview} If you can keep your rain barrels in the shade, you can starve the algae and keep it from blooming.^{[2]
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- You could even grow large, bushy plants on or around the rain barrels to provide extra shade.

2

Use the water in the barrels every 5 to 7 days.

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Try not to keep a full rain barrel for more than 5 to 7 days at a time. The more often you use the water, the less time the algae will have to establish itself.^{[3]
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3

Clean your gutters.

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Dirty gutters can bring germs and algae down into your rain barrels. Since the rain water runs from your roof, down into the gutters, and then down into your rain barrel, make sure the pathway is clean. Regularly clean your gutters and keep them free of debris to avoid algae blooms.
- Gutters are usually the dirtiest after a heavy rain. Be sure to check out your gutters after a big rainstorm to make sure they aren’t clogged.^{[4]
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4

Remove debris from the rain barrel screen.

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Rain barrel screens help prevent algae from blooming. Rain barrel screens are small, mesh screens that fit on top of or right inside the barrel itself. Most rain barrels come with a screen—if yours doesn’t, buy one and install it as soon as you can to catch debris. If you’re using one, regularly clean it out to prevent algae from establishing itself.^{[5]
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- Rain barrel screens are also a great safety measure. They prevent children and small animals from falling inside of your rain barrels.

5

Clean your rain barrels once a year.

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Deep clean your rain barrels annually to prevent algae from establishing. It can be a pain to clean your rain barrels, but fortunately, you only need to do it once a year. Dump all of the water out and use a soft scrub brush to scrub the inside. Use a few drops of dish soap or detergent to quickly clean out your rain barrels.^{[6]
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- Fall is a great time to clean your rain barrels and get them ready for the rainy season.

6

Rinse the barrels with diluted bleach once a year.

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Bleach safely disinfects your rain barrels and kills algae. If your rain barrels are very dirty or you notice a lot of algae in them, make a bleach solution using ³⁄₄ c (180 mL) of bleach for every 1 US gal (3.8 L) of water. Scrub the inside of your rain barrels using the bleach solution, then rinse them out thoroughly before setting them back up again.^{[7]
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- Using very diluted bleach in your rain barrels won’t harm your plants or your garden, especially if you rinse your barrels out thoroughly. Diluted bleach is even used to purify drinking water in some cases, so it’s perfectly fine to use around pets, children, and plants.^{[8]
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- If you’re not comfortable using bleach, you can also use white vinegar. Make a 1:1 ratio of white vinegar and water, then use it to clean out your rain barrels as a natural disinfectant.

7

Store the barrel upside down in winter.

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During the winter months when no rain is falling, dump the water out of your rain barrels and flip them upside down. Keep them in storage until the temperatures stay above freezing to avoid any damage to your rain barrels.^{[9]
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Community Q&A

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Question

I use rainwater on my garden. Algae builds and stops up my drip irrigation system. What can I do to prevent this and still be safe for my garden foods?

Community Answer

Algae requires light to grow. Is your tubing or rainbarrel clear or light colored? Is it possible to set a planter on top of the barrel or to otherwise shield the barrel from light exposure? If you are using clear irrigation tubing, I suggest switching over to black flex tubing or solid tubing that prohibits light when replacing parts next time. In the meantime, you likely need to detach the barrel and use a bit of bleach first to kill what has grown in your system. I'd stick a few piece of old screening near the exit to catch random particles, or maybe set up a gravel/sand filtration process inside your rain barrel. After that is done, then shield the stored tankwater from all sun.

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Question

Is algae detrimental to your pets?

Hannah Madden

Community Answer

Yes, large quantities of algae can be toxic to animals if they ingest it. If you know there's algae in your rain barrels, keep them covered, and don't let your animals drink from them.

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