Will Bath Water Hurt Indoor Plants?

Sustainability is a consideration in many industries, with gardeners around the world wondering what part they can play in helping the environment. Reusing grey water (recycled water from your home such as bath water) is commonly recommended to save resources and cut down on your water bill at the same time. But considering the many chemicals used in the bath, it’s understandable to worry about what using bath water will do to your plants.

Bath water will not hurt your indoor plants if used correctly and for short periods of time. Ingredients in certain soaps can seriously harm your plants, so it’s essential to check the ingredients on your products before using bath water for your indoor plants.

If you watch out for certain harmful products and supplement with regular watering, you can recycle your used water, helping your plants and the planet at the same time.

How to Use Bath Water on Your Indoor Plants

The term bathwater means precisely what you’d expect: the water left over after someone takes a bath and does not drain it.

Using bathwater can be a great alternative to tap water, helping you save on your water bill. It’s particularly helpful if you’re in a drought-ridden area where access to water is scarce or restricted. 

Contents of Recycled Water

The quality of the bathwater may vary depending on the products you use in the bath, from soaps to cleaners. Luckily, soil can often filter out these products, and sometimes the residue left can function as a mild pesticide. 

If you keep used bathwater in the tub for too long, bacteria can grow that negatively impacts the quality of the water. To keep bacteria from growing, use bath water within 24 hours. You can keep it in your bathtub, sink, or container such as a bucket for short periods.

Bath water shouldn’t replace regular water, but it is okay to use it for a short time if needed. 

Plants May Be Affected by Direct Contact

The Royal Horticultural Society experimented on several plants and found that the use of bathwater for a few weeks didn’t have any adverse effects. However, after six weeks, some plants showed signs of salt stress. 

Before using the bathwater on any of your plants, you’ll want to assess how your particular species will handle it. Some plants are fussier than others and don’t like changes in the environment, such as fiddle leaf figs. Watering these plants with bath water can have quicker negative impacts than in other houseplants.

Depending on the type of soap and shampoo you use, you may notice signs of damage on the foliage when watering overhead. When using the bathwater, pour it directly into the soil and avoid the leaves so that they don’t get damaged by direct contact with the soap. 

Soaps That Could Harm Indoor Plants

If you decide to use bath water to water your indoor plants, you’ll want to be careful about using certain soaps.

The most common soap ingredients that are harmful to houseplants are: 

  • Sodium hydroxide
  • Sodium lauryl sulfate

Sodium Hydroxide

Sodium hydroxide is a corrosive chemical common in many hygienic soaps. This chemical is in many soaps because it is highly effective in removing dirt and grease, but this property can also be harmful to your plants.

Plants are covered in a waxy substance for protection. Sodium hydroxide can eat away at that protective layer, increasing the risk of various problems like pests and diseases that may kill the plant.

Similarly, you should never use dishwater that has dish soap in it to water your plants. Ingredients in dish soap can also be extremely harmful to your plants. 

Sodium Lauryl Sulfate

Sodium lauryl sulfate (SLS) is a surfactant commonly found in soaps. According to the experts at the University of Queensland, this compound is a known irritant to human skin after extended use. This information made many people believe that if it can negatively affect our skin, you won’t want to put it on your plants, either.

Although it might seem alarming, studies have shown that SLS is readily biodegradable and doesn’t persist too long in the environment. It also doesn’t affect underground plant parts negatively. However, it will likely harm plant shoots when exposed for too long.

Soapy Water Can Deter Insects

In addition to watering your plants with bath water, using particular soap and water mixtures can also deter bugs that cause harm to your plants. You’ll want to use soap intended for laundry or bath use and watch out for the harmful additives mentioned above before use. 

The easiest way to make a safe soap mixture to deter insects is to follow these simple steps:

  1. Grate one bar of soap into a pot.
  2. Add 1 quart (0.95 liters) of water.
  3. Bring to a boil until the soap is dissolved.
  4. Pour the mixture into a type of storage container.
  5. When using the combination on your plants, mix one tablespoon of the mixture into a spray bottle full of water.

Using a soap mixture on your plants is a great way to deter insects. Don’t use bar soap with a strong fragrance, though, as this can also harm your plants.

Some insecticides are safe for plant use, such as Garden Safe Insecticidal Soap Insect Killer (available on Amazon.com). This product is affordable and completely safe for any plants you may have. The spray is organic and doesn’t have harmful ingredients in it. 

Another great option is the Natria Neem Oil Spray For Plants Organic Disease Control from Amazon.com. This product is primarily made from neem oil, an ingredient that helps deter pests.

Watering Plants in the Bathtub

So, if you’re using bathwater, you may be wondering if you can put your plants in the tub to water them. The answer is yes, you can, using a technique called bottom watering. This technique prevents your plant shoots from getting into direct contact with potentially harmful substances.

Simply set your plant right in the bathtub in a pot that has drainage holes. The potted plant should be able to sit on the bottom of the tub—not floating—and still soak up water. A couple of inches of water should be suitable.

Leave the potted plant in the water for about 10 to 30 minutes, depending on the size of your pot and plant. This will allow the plant to absorb the water through the base, saturating the soil. After this, you can return the plant to its regular spot in your home. 

This watering technique will likely bring some insoluble salts up to the surface of the soil. That’s why it’s important to remember that bath water can be used only as a temporary water source for plants.

It’s best to top water your potted plants on the next watering cycle using rainwater, distilled water, or filtered water. Doing so will flush unwanted mineral buildup in the potting mix.

If you are interested to learn more about bottom watering, you can read my beginner’s guide here: How to Water Plants from the Bottom (Beginner’s Guide)

Conclusion

When used correctly and not for long periods, bathwater is not harmful to your indoor plants. However, you need to pay attention to the ingredients in the soap that may be in your bathwater to prevent damage.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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