How Long Can You Store Rainwater for Plants? (The Best Guide)

Rising water prices can affect the humble gardener’s ability to produce bountiful yields. The solution can be as simple as storing precious rainwater for later use. Using rainwater for your plants can pose some issues, though.

For example, the average lifespan of stored rainwater can be as little as 1 week if not stored correctly. That’s why it becomes important to know exactly how long can you store rainwater for plants?

In simpler words, you can’t store rainwater in a lower volume and a stagnant state for more than 1 week to be honest, regardless if it’s used on indoor or outdoor plants.

The rainwater can become contaminated and therefore be deemed unusable. The greatest risks to stored rainwater are light, pollution and intruders such as animals and/or insects. Light can attract bacteria and spoil all water stores.

Pollution from chemicals, twigs/leaves, and other foreign debris can spoil stores with even the smallest amounts.

How long can you store rainwater for plants
How Long Can You Store Rainwater for Plants?

Animals and insects can do equal damage as they use the water as a drinking source or breeding ground. In this article, our detailed research will help you discover how long you can store rainwater for plants, including the risks and tips. 

Is stored rainwater good for plants?

Rainwater is classified as soft water. Meaning that it contains lower levels of minerals such as calcium and/or magnesium. Stored rainwater is much more beneficial to plants than town piped water.

It can also help lower the pH value of the root zone, which as a result, regulates nutrient availability. Town water, on the other hand, contains higher levels which can cause problems with extended use on plants.

How long can you store rainwater for plants?

Multiple factors can determine the lifetime of stored rainwater. In general, rainwater in a lower volume and a stagnant state will last no longer than 1 week. After this time, bacteria can start forming and the operation can become a disaster.

Surprisingly, sunlight can have a huge impact on the state of the water.

Rainwater storage is a delicate subject. You can get away with using just simple barrels or containers if you plan to use the stores more frequently.

You can store greater amounts of clean, fresh water for longer. Frequent water changeover ensures that it doesn’t stay stagnant for long periods.

Stagnant water is essentially the perfect breeding ground for bacteria. Alternatively, spending a little extra time, money and energy to plan long-term water storage is, extremely beneficial.

How long can you store rainwater for plants

Microorganisms and insects thrive around water with sunlight and will, more often than not, start their little civilization in these conditions. These cheeky little buggers can also get into small cracks or splits in the storage container and cause the same issues.

Additionally, debris such as twigs, branches, leaves, grass, etc. can cause blockages and build, which the bacteria can use as a base. Ideally, if you were to have a completely sealed and waterproofed concrete tank that doesn’t receive any light, these issues can almost be eliminated.

Alternatively, a container with a tight-fitting lid that blocks light can also achieve better results. Even installing a filter can assist with keeping out any nasties as the water enters the container. 

Using contaminated rainwater on your plants is not ideal, considering the damage it can cause. They cripple the cell membrane, which destroys chlorophyll.

As a result, this reduces the plant’s ability to utilize photosynthesis. In simple terms, the plant’s ability to grow is severely hampered. The leaves grow smaller and more compact, the stems become leggy, and the colors aren’t as green and vibrant.

What Makes Rainwater Unsafe For Plants?

Multiple factors can deem rainwater unsafe for plants. When rainwater sits in its storage container, it usually becomes stagnant. Stagnant water is, of course, water that isn’t constantly moving. The problem isn’t the stagnation of the water, though.

What Makes Rainwater Unsafe For Plants?

If rainwater isn’t stored correctly for longer than 1 week, it will more than likely become contaminated. Again, it’s more if the rainwater isn’t protected from the risks noted below.

Direct Sun Exposure

If the stored rainwater is exposed to direct sunlight, it becomes an incubator for parasites, bacteria, mosquitos, and other insects. These small armies can form on or in any small pools of water. The added sunlight to these pools of water allows perfect humid conditions for eggs to hatch and spawn.

Once they establish themselves, they are extremely difficult to eradicate. You need to remove all the water, disinfect the whole container and fill it up again. 

Algae and Bacterias

Algae and bacteria don’t need direct sun exposure to grow; sunlight will enhance their growth rate in some cases. The growth rate can vary depending on the strain of the microorganism. Most strains have a doubling time limit of around 30-60 minutes.

Of course, it all depends on the growing conditions and if there are any other contaminants present to speed up the process. 

Mosquito Breeding Ground

Stagnant water is the perfect breeding ground for mosquitoes. Water is required for the eggs to hatch into larvae. Additionally, when the water is stagnant, it contains organic matter for the larvae to feed on. It also allows them to breathe oxygen just above the surface.

So they don’t need to move while they grow big enough to fend for themselves. The female mosquito will buzz around in search of an area like this so she can assure that her young can survive and thrive. 

Air Pollutants in City

There are a range of invisible pollutants floating around in the city air that can cause some real damage to your rainwater stores. Pollutants such as carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead are the main culprits.

They can cause rainwater to become more acidic and even cloudy. There are also issues surrounding the rainwater’s path from the sky to the container. For example, in the collection, the rainwater can pass through zinc roofing, rusty pipes, wood and debris, etc.

These heavy metals and other remnants should be mitigated to reduce contamination issues.

Dead animals

Dead animals are a huge problem in rainwater collection areas. The bacteria, parasites, and other nasties that feed on the rot and decay release toxins, ultimately killing your plants. They are also really difficult to remove.

Animal faeces can also pose risks, especially in areas with low levels of rainfall, such as deserts. Whatever type of container used to store water should always be sealed, and any openings should be clear of access to animals. 

What Makes Rainwater Unsafe For Plants


Insects can cause blockages in pipes and carry around disease or even pollen. The pollen spores can form algae which contaminate the water. An effective water storage container shouldn’t offer any form of entry for anything other than rainwater. It should be tightly sealed and waterproof.

How do you check if the Rainwater is still safe to use?

You should know how your rainwater collection system is set up and how well it has been maintained. This will give you a rough indication of the quality of your rainwater. You can check to see if it’s safe by smelling it; it should have little to no smell.

Also, make sure it looks clear and not discolored. You can also use a simple pH testing kit to measure and rule out any hard swings towards acidity or alkalinity. 

Best Ways to Preserve Rainwater Longer to Keep It Clean and Fresh for Plants?

Collecting and storing rainwater can seem a little overwhelming. But with the proper skills and knowledge, it can be super simple and fun! They can save you a ton of time, energy and money; your plants will love you for it! Let’s look at some methods to help preserve your rainwater for longer.

Best Ways to Preserve Rainwater Longer to Keep It Clean and Fresh for Plants?

Use Proper Collection Tools

When creating a rainwater harvesting system, 6 main components should be considered. These components require specific tools to effectively capture clean rainwater. Some more advanced parts can be used if the water is used to drink later. These include:

  1. Catchment – You would generally use a surface such as a roof to catch larger amounts of water. 
  2. Conveyance – You would then strategically set up piping channels to deliver water from the catchment area to the storage area.
  3. Roof Washing – As the water moves from the catchment area, guttering with pipe filtration can be added to help remove any larger debris.
  4. Storage – This is where your planning must be on point. Your workable space and desired volume need to be considered. A tank or system is used as rainwater storage. It should be sealed to prevent intruders and floating/flying debris.
  5. Purification – This can include a filtration system and/or ozone/UV light to further purify the water. Your usage will govern this step. The cleaner, the better, but extreme purification may not be necessary for plants.
  6. Distribution – The way that the rainwater leaves the tank to be able to be used on your plants. For example, a pump or pressure tank can be installed to pump out the water into a tap and hose. 

Protect with Tight Fitting Cover

Given that the plants on which you use the rainwater could be your only source of food, you want to protect the water source as best as possible. A tight-fitting cover with a sealed pipe inlet is essential to keeping insects and other pesky animals from having access.

Anything that can wriggle its way in can also die there, which is one thing you want to avoid. A Tight-fitting cover also keeps organic matter such as tree branches and leaves, grass, and other foliage.

 Install a Filter

Installing a water filter isn’t essential. The need for one depends on several factors, including the location of the water; it may be in a dam or pass through an old pipe system that needs filtration.

The temperature of the water can also affect the water quality because if the water is warmer, it can form algae and assist bacteria in creating a spawn point.

The surrounding conditions are another factor that can require a filter. The rainwater may be stored near another contaminant or even some chemicals (not ideal). So installing a filter can remove the guesswork about whether the rainwater is okay to use.

Add Chlorine/Iodine Tablets

Chlorine and/or iodine are chemicals that can assist in the deactivation of bacteria, viruses and parasitic protozoans. If the process is completed correctly, these contaminants won’t be an issue for plants or human consumption. You can usually purchase both chlorine and iodine in tablet form to assist with dosage. 

Use Mosquitos repellent Oil

Certain oils can be used to deter mosquitoes from forming an army in your rainwater stores. These include olive oil, horticultural oil and dormant oil. Simply add them to the storage containers.

They are usually organic and have no harmful chemicals, but it’s always a good idea to check before use. Another physical barrier that can be used to compliment the oils is fine mesh netting. The oils are the first port of call, though.

Keeps light out by Painting

Light becomes an issue if intruders get the chance to reproduce, which is usually quite often. The light speeds up the spawning process of bacteria, parasites, insects, etc., by acting as an incubator. You can use darker colored paints to block the light cast on our storage tanks.

Try to purchase an approved, long-lasting product that doesn’t chip or fade. The best options are exterior latex house paint or elastomeric paint. They tend to stay flexible as they dry. They also allow the tank to expand and contract without losing its strength. 

Best Ways to Preserve Rainwater Longer to Keep It Clean and Fresh for Plants

Frequently Cleaning and Maintenance

If you have a smaller, simpler water storage system, you will need to try to recycle the water more often. The water is ok to sit there for around a week, but no longer; otherwise, it can become contaminated.

If possible, bi-monthly flushing and cleaning will help reduce this risk. Simply disconnect the tank and empty the water before disinfecting the tank. Once the storage container is clean, reconnect it and fill it as usual.

Frequently Asked Questions (fAQs)

Should I add bleach to my rain barrel?

Bleach can be used as a method to deactivate bacteria, viruses and parasitic protozoans. Unscented household bleach with a 5-6% chlorine solution is best. Add 1/8 teaspoon (8 drops) of bleach per gallon of water. 

How long does nitrogen stay in rainwater?

Nitrogen can get into rainwater via certain reactions caused by heat and pressure. The nitrogen in the rainwater can last until the plants can use it. It’s beneficial to their growth, and the amount in rainwater storage is minimal. 

Do rain barrels grow bacteria?

Rain barrels can grow bacteria. Remember, the collected water has a journey that usually begins in a catchment area like a roof. Then it travels through a series of pipes to its resting place.

This journey has the potential to pick up a range of microorganisms such as bacteria, parasites and other smaller intruders. The barrels are where the bacteria have a chance to breed and grow. They can be minimized if they have been set up correctly with filters and other cleansing protocols. 

Can I water plants with old rainwater?

Using old rainwater is possible as long as the collection, filtration, and storage methods are well planned. If you’re just running a pipe from your roof into a barrel without the correct measures, it will only be used for around a week before becoming contaminated. If this is the case, using contaminated rainwater is not a good idea.


Rainwater is a great free source of water for your plants. Your plants can benefit if you can create a system that allows you to store larger amounts for longer periods.

Stagnant stored water inside a small container, such as a barrel, can become contaminated after a week. This is worth noting when planning your use. We hope that this article has been helpful.

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