Many people store rainwater and use it to water their plants. However, water can’t be stored forever, even if it will only be used to water plants. How long can water being used to water plants be stored?

Rainwater that is being used to water plants can be stored for one week before it becomes contaminated and can’t be used. It can be stored for longer if stored in a sealed, darkly colored container. Check for mosquitoes and algae before using rainwater to water plants.

Now that you know about how long you can store rainwater that you can use to water your plants, you are likely wondering why you should only store it for a week. Keep reading if you want to find out why.

How Long to Store Rainwater for Plants?

We can only store rainwater for about a week because after that, it can become contaminated by a variety of animals, pests, and growths. Although it may not seem like, you can still use contaminated water to water your plants, especially if they aren’t edible, you shouldn’t because they can kill the plants that you use the water on.

Make sure you don’t use contaminated water on plants that you are planning on eating, like tomatoes or carrots. If you use contaminated water, it will contaminate the plants and when you eat them, they may harm you and cause you to become sick.

With a specialized collection tank that is tightly sealed at the top, one can store rainwater from 4 weeks to 8 weeks. However, it’s important to note that still water is the ideal breeding ground for mosquitoes, larvae, and algae. Hence, it’s crucial that the stored rainwater is used regularly and the storage tank is cleaned frequently. – Karan Mahajan, Co-Founder, All That Grows

If you use contaminated water on plants, then when the plants grow, they may be discolored, their growth stunted, or cause your plant to die depending on how contaminated the water is and what contaminated it.

However, if you store rainwater correctly, you can store it for longer than a week. You can potentially store it for years, as long as nothing gets into it or starts growing in it.

You might store rainwater forever, although it will become stale and may smell, so you will want to store it for a short period, even if you are just using it to water the plants.

Now that you know how long you should store rainwater when you are going to use it to water plants, you are likely wondering why it should only be stored for a week. Keep reading to find out.

I asked fellow gardeners if they store rainwater for plants and what they do to prevent contamination. 74% do prefer to store this water as you can see below.

Why Should Rainwater for Plants Be Stored for a Short Time?

Rainwater should only be stored for a week because algae, mosquitoes, and animals can contaminate it.


Algae bloom in water when it is exposed to light, and rainwater is typically kept in barrels that don’t block out light, so it will form after about a week. It will bloom faster if the rainwater that you have collected is in a clear container.

If you water your plants with water that has algae in it, don’t use it because the algae will form a barrier on the topsoil near the plant you watered. This barrier will prevent water from getting to your plant’s roots, and your plants will eventually die from lack of water.

So water doesn’t have an expiry date, but can become contaminated if not stored properly. So the more consideration one puts in the way they store water, preventing algae and mosquitoes, the longer the shelf life of the rainwater. – Vinayak Garg, Founder, Lazy Gardener


Mosquitoes lay their eggs in water, and most containers that people store rainwater in have small openings that they use to get into the water.

If you are going to use some rainwater that you have stored to water your plants, make sure you look for evidence of mosquitoes and mosquito larvae around the edges of the container that the water is stored in before you water your plants.

I make wooden frames with screens that seem to keep the mosquitoes at bay and use the slime at the bottom to water around my fruit trees and clean out when the rainwater starts to dry out. The garden seems to thrive on rain water but it is necessary to use tap water when there are dry spells. – Bill

Mosquitoes won’t harm your plants if you use water with mosquito larvae in it, but it will cause more mosquitoes to be near your home and potentially bite you, which will be detrimental to you if they are carrying the West Nile virus, dengue fever, or malaria.


Animals need water, and they will try to get into any container that is storing rainwater. If animals drink the water you collected and then fall in, they can drown and contaminate the water. Mice, toads, and small animals often get into stored rainwater, although the toads likely won’t drown in the collected rainwater.

Although rainwater should only be stored for about a week, there are ways you can preserve the rainwater that you have collected so you can use it after a week has gone by. Keep reading to find out how.

How to Preserve Rainwater for Plants Longer

If you want to store the rainwater that you collected for longer than a week, there are a few things that you can do to prevent bugs, animals, and other things that will contaminate the water.

Purchase a large barrel that is approved to store liquids. The darker the color of the barrel, the better. If possible, before you store water in your rain barrel, paint it brown or black. The paint will prevent light from coming through the barrel and prevent algae from blooming.

Rainwater for plants can be stored for a very long time, assuming certain precautions are taken. The problem comes in when the water is exposed to light, insects, or other types of debris. This exposure leads to contamination, which can mean foul smells or mosquitoes. I recommend collecting just enough rainwater that you will use in one or two weeks. This short time will minimize the problems associated with water being exposed to the open air. – Brian Walker, Founder, Landscape Tutor

Most rain barrels are opaque, so they let light in even if they are a dark color. The paint will prevent light from coming through without contaminating the water. However, if you paint your rainwater barrel a dark color, the sun will heat the water and make it an ideal place for mosquitoes to breed.

If you want to prevent mosquitoes from getting into the water and prevent the water from getting warm while it is in your rain barrel, keep it out of the sun and cover the top with a lid that fits tightly over the barrel. If possible, tape the lid to the barrel all the way around to seal any small openings. The lid will prevent any animals from getting into the water.

If you want to prevent mosquitoes from getting into your collected water, put one tablespoon of vegetable or fish oil into the water you have collected. The oil will stay on the surface of your collected water and prevent mosquitoes from breeding in the water.

Before you use the rainwater you collected to water your plants, smell it and make sure that it doesn’t smell like rotten eggs or like something has grown or gotten into the water and contaminated it. If your plants are sensitive to pH levels, check the pH levels of the water before you use it to water your plants.

Overall, you should only keep rainwater for about a week, but you can store it for longer if you store it in a sealed container and prevent bugs and animals from contaminating it.

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