Can Rain Barrel Water Go Bad?

This rain barrel's water has not gone bad

Being an avid gardener, my wife loves to water her flowers using the rain we collect in our patio’s rain barrel.

However, we found out the hard way that if you don’t take proper precautions, your rain barrel can fall victim to all sorts of undesired conditions. One moment we were using the cloud’s bounty to grow our plants. The next, we had an insect infested reservoir that smelled like rotten eggs. To answer the question, rain barrel water can go bad.


We wrote an entire rain barrel buying guide for 2020. If you’re in the market, consider giving it a read!

What Happens?

First, I should note that the water itself doesn’t actually expire like milk would expire.

However, your rain barrel isn’t a closed system. Bacteria, insects, algae, and other contaminants can breach the outer perimeter of the barrel and set up shop inside. This normally isn’t a problem — bacteria is literally everywhere and a small amount of insect/algae contamination won’t be enough to hurt your plants. The problem occurs when the water remains stagnant and unused for many weeks (the same problem happens in bird baths).

Sitting water is a breeding ground for foul-smelling bacteria, mold, parasites, and unwanted insects (like mosquitoes). While these things are unlikely to hurt your plants, they’re unwelcome and can cause major problems/illnesses for pets, small children, and even adults.

How To Prevent Rain Water From Going Bad

You have a few options to prevent your rain barrel water from going bad. Each have their pro’s and cons, but one in particular is preferred. First, let’s cover the preferred approach.

Regularly Cycling Water

Do you remember the expression “a rolling stone gathers no moss?” Well, the same truth can be applied to rain barrel water. Since the problems only start to surface when the rain water is stagnant, you can easily avoid the problems by making sure the water keeps moving. To do this, simply remember to use your rain barrel often while draining it if the water ever sits for too long.

Bleach / Chlorine

If you already have contamination in your rain barrel, a small amount of bleach or chlorine will kill the parasites and bacteria. As long as you use the proper amount, it shouldn’t bring any additional danger to pets or people. What’s the proper amount of bleach to sanitize a rain barrel? The CDC‘s rule of thumb is 1/8 tsp – 1/4 tsp of bleach per gallon of water. You’ll want to adjust the amount depending on the size of your rain barrel and the level of contamination. To save you a bit of arithmetic, I’ve compiled this handy table.

# of GallonsAmount of Bleach
502 – 4 tablespoons
1004 – 8 tablespoons
2001/2 cup – 1 cup

To know whether you should use the first number of the second number, you should evaluate the water quality. If it’s cloudy or discolored, I’d suggest using the second number. If it’s otherwise clear, you can probably use closer to the first number.

For chlorine, the calculations change: 4mg per liter. To figure up how much we’ll need to use, we first have to convert it to imperial units. Again, here’s a handy chart to help things along.

# of Gallons# of LitersAmount of Chlorine

Why Does My Rain Barrel Smell Like Rotten Eggs?

Folks are generally confused when their rain barrel starts smelling like rotten eggs. If the water is coming from the sky, how can it be imbued with the smell of sulfur? Well, when the water trickles down your roof and into your gutter, small plant particles are brought down with it. If you don’t have a filter going into your rain barrel (or if your filter is too large), those particles can get inside. As the bacteria consume these organic compounds, the smell of rotten eggs is produced.

If your rain water barrel smells like a rotten eggs, it’s a really good sign that you should either add some bleach or clean out the water and sanitize. However, if you’re reasonably sure that your rain barrel water is still safe, you can simply choose to mask the smell.

How To Keep Rain Barrel Water From Smelling

There are a few things you can try in order to keep rain barrel water from smelling bad. My favorite idea is to put live mint plants inside the barrel and wait for nature to do it’s magic. Mint plants will generally take root in anything, so they’re a great candidate for covering up a stinky rain barrel.

If you don’t have a mint plant handy (or if you simply lack a green thumb), you can add some baking soda to the barrel each time you drain it. Baking soda is another natural odor eliminator and can do wonders for your rain barrel.


I'm Chuck (the Captain). I'm passionate about my outdoor space and love sharing my experiences with the world at large. I want Captain Patio to become the best place on the internet to find, share, and learn about all things patio-related. When I'm not keeping up my content schedule, I'm spending time with my wife and two kids (usually on my patio!).

3 thoughts on “Can Rain Barrel Water Go Bad?

  1. Pingback: How to Keep Your Rain Barrel From Stinking | Captain Patio

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