Can You Water Your Plants With Dishwater?

There is an increasing number of environmentally conscious people in the world, aiming to reduce wastage of precious resources. For gardeners, one of the popular ways to do that is by using greywater – recycled water from your home – in the garden. However, is dishwater safe for use on your plants?

Unfortunately, you cannot water your plants with dishwater. Although reusing dishwater can help reduce waste, the disadvantages far outweigh the benefits, from harmful chemicals to the inclusion of food particles in the soil.

This article will explain why dishwater is not safe and what you can do to make it safe if you want to give it a try.

Greywater and Its Sources: An Overview

One popular way to reduce our negative impact on the environment is to find ways to utilize waste products. That’s why many people have resorted to using household wastewater for gardening or agriculture.

Cloudy or dirty wastewater is often referred to as greywater due to the presence of residues.

Some sources of greywater at home include:

  • Dishwater from the dishwasher
  • Water from the kitchen sink
  • Laundry water
  • Water from shower drains
  • Water from bathtub drains
  • Water from bathroom sinks

Across the US, many households generate significant amounts of wastewater daily, which goes into the community sewer systems. The wastewater is then transported to a treatment facility, where it is treated to remove most organic and large solid waste particles.

The treated water then goes back to homes for non-potable uses, such as in agriculture or home toilet flushing. This system is common and beneficial for areas with a limited supply of fresh water, especially those that require intelligent ways of recycling wastewater. 

Why Dishwater May Be Unsuitable for Plants

Water treatment facilities are vital for communities, as they help prevent the contamination of natural freshwater bodies like rivers and lakes and provide alternative water sources during severe drought or water shortages.

However, many communities lack this system, and residents may try to collect dishwater by themselves for garden use. Although it seems like a clever way to recycle dishwater, it is not recommended.

It is not safe to water your plants with dishwater because it may contain food particles, harmful microorganisms, or toxic chemicals from your dish soap. If you use dishwater directly to water your plants, you are skipping the essential wastewater treatment that helps remove these contaminants.

Moreover, even if there is a water treatment system, the technology may be insufficient in reducing or eliminating harmful contaminants or pollutants. 

Let’s look further into how these factors make it unsafe to water your plants with dishwater:

Dishwater Contains Food Particles

Leftover food particles attached to your cookware and utensils will drain along with greywater after using your dishwasher. These particles may attract insects and rodents to your garden and may damage your plants, depending on the food source.

In addition, decaying food particles or organic matter may also promote the growth of fungi or mold, which can impact plant growth and may be dangerous when inhaled by people with hypersensitivity. 

This is especially true if you use dishwater for indoor plants. The fungi will eventually create spores and contaminate your indoor air, effectively reducing its quality.

Greywater May Contain Harmful Microbes

Untreated dishwater may contain harmful microorganisms, such as bacteria and fungi. These pathogens typically come from improper food handling and poor hygiene.

Using dishwater contaminated by pathogens to water edible plants like leafy vegetables and fruits may pose serious health risks to the people who consume them.

Some common pathogens found in dishwater include:

  • Escherichia coli
  • Pseudomonas aeruginosa
  • Stenotrophomonas maltophilia
  • Acinetobacter baumannii
  • Candida
  • Cryptococcus

Once these microbes get washed along with dishwater and are introduced to the garden, they may thrive and cause infections in immunocompromised humans and animals.

Chemicals in Dish Soap Are Bad for the Soil

Many gardeners use diluted dish soap to kill and ward off insects and pests from their plants. In small amounts, this isn’t particularly dangerous to plant growth.

However, the large amounts of soap used in dishwater are not great for soil health, especially when applied regularly as you would when watering.

Many dish soaps or detergents used in dishwashers contain excessive salt that can be bad for the soil and plant roots. Temporary and short-term use of dishwater for plant watering needs may not cause serious problems, but long-term application of salt-rich dishwater can burn roots, cause nutrient imbalances and impact soil texture.

Moreover, if your dishwasher or home water filtration system uses water softeners, it can introduce more sodium into your dishwater. The high levels of sodium from your water and dish soap can be detrimental to your plants, especially if used frequently over time. 

Setting up a Greywater Irrigation System Can Be Costly

Another downside to using dishwater for your plants is that it can be costly to redirect a built home’s drainage pipes from sewer lines to your garden’s irrigation system. That’s why it’s best to consider greywater recycling before constructing your home.

Nonetheless, even if you already have a built home but still want to set up an irrigation system using the water from your dishwasher or kitchen sink, it is possible. But it will take some time to set up and can prove costly to set up your own filtration system.

Maintenance and efficiency of your greywater irrigation system is also something to consider. The system typically removes most organic materials and contaminants from the water but may not be able to remove every harmful substance.

Depending on the wastewater regulations in your community, you might also need to regularly test the quality of your greywater to ensure that it won’t pose any threats to the environment.

How to Make Dishwater Safe for Your Plants

Some states have regulations regarding proper wastewater disposal or management and may not permit households to use greywater for irrigation. So if you’re planning to start a greywater irrigation system for your home garden, make sure you check with your local authorities first.

If your community allows it, you can start carrying out strategies to make dishwater safe for your plants.

Use Dish Soap That Is Safe for Plants and Soil

Check the ingredients on your dish soap or detergent, looking for environmentally-friendly ingredients that won’t harm your plants. It’s crucial to use a cleaning product that contains little to no salt (sodium chloride). Dish soaps that contain bleach can also be toxic to plants.

Despite their sodium content, dish soaps containing sodium lauryl sulfates (SLS) are safe to use because the chemical is water-soluble and biodegradable, breaking down into non-toxic forms by the time it reaches your garden. 

Don’t Use Dishwater on Edible Plants

When using any greywater (including dishwater) for your plants, it is best to install an underground irrigation system. It will prevent the water and potentially harmful contaminants from touching the edible parts of your plants, such as leaves, flowers and fruit.

The underground irrigation system also keeps the water close to the roots for absorption, reducing the risk of contact between humans and pathogens during gardening activities.

Final Thoughts

Dishwater is not ideal for plants because it typically contains contaminants that can harm your plants and garden soil. 

There are ways to make dishwater safe for agricultural irrigation, such as using a water treatment system. However, it can be costly and challenging to install and maintain. Ultimately, it’s better to avoid using dishwater, opting for other environmentally-friendly water sources instead.

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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