Skip to Content

Is Greywater Good for Plants?

Please share!

*This post may have affiliate links, which means I may receive commissions if you choose to purchase through links I provide (at no extra cost to you). As an Amazon Associate I earn from qualifying purchases. Please read my disclaimer for additional details..

If you’re an avid gardener or just a plant lover, chances are you have heard about greywater. Those new to gardening might scratch their head when you ask whether they are using greywater for their garden or plants.

Simply put, greywater is the domestic wastewater that comes from sources such as washers, bathtubs, bathroom sinks, and even showers.

However, don’t confuse greywater with sewage water, which is called blackwater.

Since plants are always in need of water to stay hydrated, can you use greywater on your plants? Or, to be exact, is greywater safe for plants?

Greywater is considered safe and can be used to water your plants.

There are two types of greywater: treated and untreated greywater.

Treated greywater can be used for different purposes, including gardening, cleaning your drain or gutter, flushing your toilet, and even washing your laundry. Because it has been treated in a proper greywater treatment system, few bacteria exist in the water. Hence, it is a lot safer to use for a longer period of time.

On the other hand, untreated greywater hasn’t been treated and is lower in quality compared to treated greywater.

senior woman watering her plants at home

What Effect Does Greywater Have on Plants?

To be honest, you can’t compare the quality of fresh, clean water with greywater. However, this doesn’t mean that greywater is bad for plants.

The use of greywater, especially with a pH level of around eight, can lead to an increase in soil pH, but at the same time, it can reduce the availability of some micronutrients that are essential for plant growth.

This conclusion is pretty subjective because the quality of the greywater is highly dependent on the content of any chemicals in the water. Hence, you should always be aware of all the products you use in your house.

There is also a possibility that chemicals in the greywater will kill most of the beneficial bacteria and bugs in the soil. However, the plants and soil will work symbiotically to filter and break down the greywater, removing as many harmful chemicals and bacteria as possible.

The sand, granulated rocks, and substrates will act as a filter by letting the water pass through, leaving the contaminants at the top of the soil. Once the nutrients and biodegradable materials have been filtered and collected, the plants will absorb and use them.

If done correctly, greywater can benefit plants in the following ways:

Maintain Moist Soil

A constant supply of greywater through an irrigation system can create a cool and damp environment. Such an environment will also promote the growth of shade trees and other plant life. In turn, the shade from the plants is more than enough to cover the soil, adding more protection from the scorching sun.

Fertilize Plants

Greywater contains skin cells and phosphorus from soaps. So it can provide plants with enough micronutrients and a beneficial microbiome.

In fact, using greywater can be like using manure. Both products are not visually appealing, but they carry the same purpose: to fertilize the plants. After microbes in the soil have broken down all the chemical compounds in the water, the plants will absorb essential nutrients such as nitrogen and phosphorus before this process is repeated.

So, greywater can act as a mild fertilizer that can improve the growth of plants.

man holding a hose watering all plants

Is Greywater Bad for the Environment?

Choosing to use greywater can be viewed as a “double-edged sword” decision. There is no denying that the water contains beneficial bacteria and micronutrients that promote the growth of plants.

However, you can’t overlook the fact that greywater also contains other chemicals that might be harmful to the soil and environment. Hence, being aware of all the products you use inside the house is imperative in gauging how harmful the greywater is.

Most of the time, excessive greywater use is bad for the environment. Here’s why:

It Can Cause Excessive Algae Growth

Greywater contains one of the micronutrients needed by algae, which is phosphate.

When there is a constant supply of greywater or, to be exact, an excessive supply of greywater, some of the water can flow into streams that lead to lakes and ponds. If enough phosphates accumulate in a lake or pond, an algal bloom can occur.

It Can Oversaturate the Soil

Oversaturation of the soil happens when plants are overwatered. Overwatering itself isn’t a good practice. However, the impact of overwatering the soil using clean water is less harmful compared to using greywater.

Since you can’t store greywater for more than 24 hours without bacteria growing in it, you tend to use all of it at once. This can cause more micronutrients or chemicals to accumulate in the soil.

It Can Alter the pH of the Soil

Untreated greywater can affect soil more than treated water can. In fact, minerals, salts, and chemical compounds found in greywater can alter the pH level of the soil. Most greywater also contains traces of cleaning products that make the water more alkaline than it is supposed to be.

Hence, you should avoid using this water on any acid-loving plants. For instance, rhododendrons, azaleas, blueberries, camellias, and ferns thrive in acidic soil. Trying to irrigate these plants with greywater will only inhibit their growth.

It Can Prevent Water Absorption

Greywater collected from kitchen sinks contains oils and fats. When you water the soil and plants with greywater, the oil will be absorbed into the soil or accumulate in parts of the plants. As more oil and lipids accumulate underground, it can prevent water from penetrating, making the soil lose its conductive properties.

soapy water

Can I Use Bathwater to Water My Plants?

Bathwater doesn’t fall in the category of sewage or water from toilets. Hence, it can be used to water your plants. You can also reduce the volume of clean water you use by using bathwater on your gardens or plants. Here’s how:

  1. Mulch the soil surface using wood chips or shredded bark around three to four inches thick. Apply and spread this mulch evenly. Mulch helps in retaining moisture in the soil. It also helps in decomposing toxic materials and filters out contaminants or small particles of solid waste in the water.
  2. Measure the space of your garden by taking into account its length and width. Divide the number by two to get the volume of water that you can safely use without overwatering or harming the soil and plants. For instance, if your garden measures around 200-square feet, the right amount of bathwater that you should use would be 100 gallons.
  3. Place the water in large containers or waterers. Remember not to keep the water for more than 24 hours to prevent bacterial growth.
  4. Water your plants accordingly. If possible, try to apply the bathwater to the base of the plant. Avoid the leaves and stems to prevent them from absorbing the water. Always use the right amount that you calculated in step two.
  5. Once you’ve watered the plants, use clean water to feed your plants for the rest of the week. This step is important to remove any contaminants or pollutants that might exist in the bathwater.
bermuda grass lawn

21 Plants That Thrive on Greywater

Don’t be surprised to know that some plants thrive on greywater. These plants love all the micronutrients that this type of water could offer:

  • Hibiscus (Hibiscus)
  • Yucca (Yucca)
  • Gardenia (Gardenia jasminoides)
  • Crimson bottlebrush (Callistemon citrinus)
  • Rosemary (Salvia rosmarinus)
  • Austrian Pine (Pinus nigra)
  • Birds Of Paradise (Strelitzia reginae)
  • Wood Iris (Dietes)
  • Cottonwood (Populus sect. Aigeiros)
  • Honeysuckle (Lonicera)
  • Juniper (Juniperus)
  • Sumac (Rhus)
  • Manilla Grass (Zoysia matrella)
  • Paperbarks (Melaleuca)
  • Buffalo Grass (Bouteloua dactyloides)
  • Italian Stone Pine (Pinus pinea)
  • Bermuda Grass (Cynodon dactylon)
  • Bearded Iris (Iris germanica)
  • Lilyturf (Liriope)
  • Rabbit Brush (Ericameria nauseosa)
  • Mugo Pine (Pinus mugo)

Final Thoughts

When watering your garden and plants with greywater, be sure to monitor their growth and how they react to this type of water. Some plants might have a hard time adapting to greywater. So, you will have to take it easy on the amount of water you use until they can adjust accordingly.

Every six weeks, use clean water to flush out any chemicals or pollutants that have accumulated in the soil. And if you can, purchase organic compost to increase the amount of organic material in the soil.


Please share!