How Long Should Water Sit Before Using It on Plants?

Many plants are tolerant and don’t mind receiving water from the tap. Small traces of chemicals like chlorine may even benefit them. However, some plants are sensitive to excessive amounts of these chemicals or sediments leftover in recycled water. Therefore, it is best to let water sit for some time before use. 

On average, you should let water sit for around 24 hours before using it on sensitive plants, primarily if you use greywater or tap water. This time will help sediments and other potentially risky substances settle to the bottom of the container, reducing the risk of your plants absorbing them. 

This article will discuss when it’s necessary to let water sit before use on plants, and when it can be avoided. I will also share alternative ways to make water safer for your plants and the best type of water to use. 

When to Let Water Sit Before Use on Plants

Rainwater is usually safe to use even without pre-treatment. Even tap water from reliable sources can be readily used on plants. However, in rare cases, they may contain contaminants and excessive salts that can harm your plants, depending on the quality of the water in your region.

In general, you can readily use tap water and rainwater on plants, except for a few situations that may require you to take necessary precautions:

During Fertilization of Houseplants

Letting water sit is necessary whenever you use fertilizers on your houseplants. Fertilizers already contain nutrients similar to those found in tap water, such as calcium, chlorine, and magnesium. 

Fertilizers are also predominantly salt. Gardeners living near coastal areas may find it risky to use rainwater on their indoor plants without pre-treatment.

Houseplants need only a small amount of these nutrients. Using tap water or rainwater during fertilization may add more of these chemicals to the soil than your plants need and can result in stunted growth or other problems.

Watering Plants That Are Temperature-Sensitive

Letting tap water or rainwater sit for a while can help regulate their temperature and make them safe for your plants.

Cold water can cause shock to plant roots, possibly stunting root growth. In fact, both hot and cold water can inhibit essential chemical reactions in the soil, as they deactivate temperature-sensitive enzymes and microbes. 

Ideally, you should feed your plants only tepid water (62-72 °F or 17-22 °C). So if you could keep your tap water within this temperature range or harvest rainwater from spring to early fall, you wouldn’t have to let them sit for temperature regulation.

Watering Potted and Indoor Plants

Outdoor plants are sturdy and can readily enjoy rainwater and water from the garden hose. In contrast, potted plants are more susceptible to fertilizer burn due to the limited growing space.

Most plants require soil with good drainage to remove excess water and leach harmful substances. However, this may not be enough to protect your potted and indoor plants from pathogens or toxic chemicals from some water sources.

The limited space in the pot and the small amount of water they receive cannot keep contaminants beyond the reach of the roots.

Factors to Consider for Different Water Sources

Many avid gardeners pay extra attention to their plants’ needs to ensure they get the best out of them. Taking care of plants can sometimes be tedious, and not all people have plenty of time or resources to meet all their gardening responsibilities. 

However, suppose you don’t have access to distilled water or find it too costly for your everyday gardening needs. In that case, it helps to pay extra attention and effort when using water with impurities. After all, water is one of the essential requirements for plant growth. 

Some people let water sit before using it on plants to let harmful substances settle to the bottom of the container. Tap water and greywater may contain pathogens or toxic chemicals, which can harm plants in excess. Meanwhile, rainwater may contain salts that can also damage your plants. 

There are plenty of accessible and environment-friendly sources available to water your plants. Some people even use treated wastewater or dishwater. However, some water types can pose serious risks for your plants if administered incorrectly. 

Tap water may require extra precautions before it becomes safe for your plant’s needs. However, it’s not always necessary. In contrast, your plants can benefit from letting other water sources like wastewater sit for at least 24 hours before use.

Let’s look at the components of different types of water and the benefits of letting them sit before using them on plants: 

Tap Water

Tap water in the US is generally safe for drinking because the Environmental Protection Agency regulates it. Most tap water in the country comes from public water systems that help ensure the water is safe for consumption. 

While it is not rare for tap water to contain contaminants, most of them are harmless.

Some may pose some risks to both humans and plants only when the levels of these contaminants are too high:

  • Microbes like bacteria, viruses, or fungi
  • Radionuclides like radon and uranium
  • Chemicals from fertilizer runoff or improperly disposed cleaning solutions
  • Biological pollutants like organic matter and sediments

It is important to remember that not all tap water sources contain these contaminants. And even if they did, the levels will significantly differ depending on the environmental conditions at individual community water systems that supply water to homes. 

Homes with private wells typically employ their own water purification systems to ensure safe and potable water access.

If you are worried about mechanical or chemical troubles that could compromise tap water quality, it won’t hurt to take extra measures to keep it safe. Sometimes, it can be as simple as letting your tap water sit overnight.

Here’s what you can do if you need extra precaution before using tap water on your plants: 

  1. Collect tap water and store it in a container. Lidded containers can prevent contamination but will require a longer sitting time.
  2. Let it stand for at least 24 hours while keeping it away from direct sunlight, especially when using a plastic container. 
  3. When it’s time to water your plants, use only the top ½ or ⅔ of the container
  4. Be careful not to shake the water in the container to avoid spreading the potential contaminants. 

If you’re aware that your local water treatment facility uses chloramine instead of chlorine, you will need more than just letting your tap water sit for 24 hours. You can use carbon filters or deionizers to make it ready to use more quickly.

Rainwater

Rainwater is the best water source for plants. It’s an eco-friendly and economical alternative to tap water for your plant’s regular watering needs. However, it is not steadily available whenever you need it. As such, some home gardeners collect and store rainwater. 

The process of collecting rainwater may contaminate it, making it unsafe for your plants. For instance, dirt on the roof and gutter can get into your container along with rainwater. Storing it in a metallic container can also result in rust. On the other hand, algae growth may occur in a plastic container. 

Depending on your region, rainwater may also contain salts, which can accumulate on your soil and affect your plant’s ability to absorb water. 

Luckily, there are several ways to reduce the potential risks of using stored rainwater for your plants.

Here are some of them: 

Boiling

Boiling the water can help eliminate harmful microorganisms since most cannot survive high temperatures (212 °F or 100 °C). 

Physical Water Treatment

The physical water treatment process requires letting the rainwater pass through several conduit systems with various-sized rocks, pebbles, and carbon filters. It can help remove some harmful elements, chemicals, and microbes. 

Chlorination

Adding chlorine to rainwater can remove many harmful microorganisms. However, it can pose a new threat to plants because many are vulnerable to high chlorine levels. 

Letting It Sit for 24 Hours

If you don’t have the means or the time to do any of the steps above, letting your freshly collected rainwater stand for 24 hours is an effective way to prevent contaminants from getting to your plants. Be sure to store rainwater in a sterile container if you keep it for extended use. 

Wastewater

Regardless of the source, wastewater needs a longer sitting time than tap water or rainwater. This waiting period is necessary because the wastewater contains more contaminants and harsh chemicals than other water sources. 

Sometimes, letting wastewater stand for over 24 hours may not be enough to isolate the contaminants that can harm your plants. This fact is especially true when using soapy water from the dishwasher or laundry machine.

Often called greywater, recycled water contains contaminants that can compromise your plants’ health. Using this water source on edible plants like fruits and leafy vegetables can also negatively affect your health. 

Using a water treatment method like filtration before using wastewater on your plants is best. You can let the treated water stand for 24 hours for extra precaution. 

Here’s a video showing how you can make a DIY wastewater filtration system: 

The Best Type of Water to Use on Plants

Rainwater is the best type of water to use on plants, especially for outdoor gardens. It’s soft water rich in dissolved oxygen and beneficial nutrients. It’s also highly recommended to apply fertilizer before a light rainfall to help work the nutrients into the root zone.

However, if you live in an area with low rainfall all year round, it can be unrealistic to store large amounts of rainwater for irrigation purposes. In that case, you will need the next best alternative.

Distilled or purified water is the best alternative to rainwater and often the preferred water type for plants like the Venus flytrap. This type of water undergoes an extensive boiling and condensation process that separates the water from all contaminants, resulting in pure water. Its purpose is to hydrate your plants without the risk of causing diseases. 

However, it may be too expensive to use distilled water if you have a large garden. That’s why many people try to find alternative water sources that are economical and eco-friendly. 

Nonetheless, it is best not to compromise your plant’s health by using risky water sources, especially if it’s your first time doing so. You should also be more cautious if you are growing edible plants. 

Since you’ll also need safe and potable drinking water for personal consumption, it helps to invest in a high-quality home water distiller or purifier. That way, you can get a steady and secure supply of clean drinking water for your family and your garden. 

Final Thoughts

Water is one of the most vital requirements for plant growth and survival. Often, plants wither or die due to watering mistakes, such as applying the wrong amount of water or using contaminated water. 

If you can’t use distilled water on your plants, you can choose from plenty of water sources available in your area. Tap and rainwater are generally safe to use even without pre-treatment for outdoor plants during warm seasons.

However, you may want to let them sit for a while before use on indoor and potted plants during fertilization season.

You can read my guide on watering indoor plants here: How to Water Indoor Plants (Complete Guide)

Written by Alexander Picot, Reviewed by Madison Moulton

Alexander Picot

Alexander Picot is the founder of TheGrowingLeaf.com and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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