En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
612 ratings

Friday - July 25, 2008

From: Nagpur, India
Region: Other
Topic: Watering
Title: Effects of greywater on plants and soil
Answered by: Nan Hampton


What are the biochemical effects of greywater in plants and soil, because both are related. The effects can be harmful and as well as beneficial, can you give me the details of that?


Greywater (or grey water) is slightly used household water—any water other than that from toilet flushing (called black water). This would include water from the dishwasher and kitchen drains, the clothes washer, showers, tubs, and lavatories. Kitchen water is sometimes put into the black water category because it contains a high percentage of oils, fats and food particles. Swimming pool drainage water is not recommended for greywater use because of its high salt concentration and stabilized chlorine or bromine which would be detrimental to most plants.

Greywater is used mainly for irrigation of plants but it can also be used for flushing toilets. Both uses contribute to the conservation of drinkable water that would otherwise be used for these purposes.

Storing greywater is not recommended unless it treated for bacterial growth; thus, greywater must be used when it is created. The water is an obvious benefit to plants, but it must be applied judiciously since oversaturation of the soil would not be beneficial to the roots of most plants. Other potential problems for plants depends on the level of the various chemicals included in the greywater. For instance, some plants will be more tolerant of greywater with substantial salinity; whereas, others may be sensitive. The chemical makeup of greywater varies from household to household depending on the personal habits of the members of the household and their choice in soaps and other cleaning solutions. Lanfax Laboratories in Australia has an excellent paper, Domestic Greywater, from their Laundry Products Research that gives data for the pH, the salinity, the sodium content, and the phosphorous content of greywater containing various clothes washing products. In general, greywater is alkaline because of the cleaning products it contains and, as such, should not be used on acid-loving plants (e.g., Rhododendrons). Unless greywater is treated, it is recommended that it not be used to water plants with edible roots and only surface watering should be used to protect edible leaves or fruits from possible bacterial exposure.

Several studies have investigated the effect of greywater on soil composition. A study by M. Travis, N. Weisbrod and A. Gross ("Accumulation of oil and grease in soils irrigated with greywater and their potential role in soil water repellency". Science of the Total Environment 394 (2008) pp. 68-74) suggests that oil and grease from greywater can accumulate in soils and affect the ability of the soil to absorb water—essentially making it water repellent. Another study by A. Gross et al. ("Environmental impact and health risks associated with greywater irrigation: a case study" Water Science & Technology Vol 52, no. 8 pp. 161-169) found evidence that: "Long term irrigation of arid loess soil with greywater may result in accumulation of salts, surfactants and boron in the soil, causing changes in soil properties and toxicity to plants."

For more technical articles, you could visit a university library and search their bibliographic databases. Also, there is a great deal of information available on the internet about greywater and its uses. Here are a few links:

Safe Use of Household Grey Water from New Mexico State University.

Greywater: what it is...how to treat it...how to use it from Greywater.com.

Grey Water Central on the Oasis Design page.

Introduction to Greywater Management from EcoSanRes.


More Watering Questions

Relocating native oak trees in compacted soil
September 14, 2008 - Can you replant and relocate small oak trees in compacted soil and will they grow or go into shock?
view the full question and answer

Watering practices for live oaks in drought from New Braunfels TX
September 04, 2011 - We have conflicting info about watering live oaks. An arborist says to water now using soaker hoses or small sprinklers and a landscaper who spoke to our garden club said that after August is too late...
view the full question and answer

Should I acidify my well water for native plants
July 15, 2008 - Should I acidify my well water for irrigation of native plants? There is not enough rainwater collection.
view the full question and answer

Is installing irrigation with Habiturf a good idea in Round Rock Texas?
December 05, 2011 - Mr. Smarty Plants, I am in the process of planning a new lawn in my front yard. We have decided to plant the Habiturf seed mix (thank you, by the way). Originally, we planned on installing a spri...
view the full question and answer

Watering live oak trees from McAllen TX
December 24, 2012 - What are the watering requirements for live oak trees in deep south Texas? How often and how many inches to be applied? One pop-up spray sprinkler spaced approximately fifteen feet away from each tr...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center