Greywater or Water Reuse

What is Greywater?

Greywater is, waste water from bathroom sinks, tubs, showers, or laundry not having wasted diapers or soiled sheets. Air conditioning condensate waste may also be considered grey water.
Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products.
In any greywater system, it is essential to use plant-friendly products without salts, boron, or chlorine bleach. These substances can damage plants.

Why greywater?

Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, thereby reducing the chance that it will pollute local water bodies.

What can greywater be used for?

Greywater may be used to irrigate ornamental plants or fruit trees. However, greywater cannot be sprayed or stored, so it must be able to be applied to the outside planting areas at time of use. Greywater can also be used to irrigate vegetable plants as long as it doesn’t touch edible parts. Therefore, it cannot be used for root vegetables such as carrots and radishes; while ground contact veggies such as squash are questionable.

What cannot be considered greywater?

Water from toilet, urinal, or kitchen sink cannot be considered greywater (kitchen sinks include meat & dairy waste and is therefore excluded).

What are the best sources of greywater?

Laundry and tub/shower are the best sources. Bathroom sink waste is often too small in volume to be cost effective if a separate tie in is needed.

Economy of Installation.

The practicality of installing a greywater system depends on the style of construction and the source of the greywater (assuming already existing construction).

  • Crawlspace under the fixture or house: Easy and cost effective.
  • Slab on grade single story homes: Usually only laundry waste is practical as tub/showers in slab construction have the waste lines below the slap and therefore inaccessible.
  • Upstairs fixtures: These may offer a ceiling to cut into and relatively easy greywater access IF:
    • the floor joists run to the exterior wall
    • the space between the wood floor supports provide a passageway to the exterior wall to exit and go down the exterior or interior wall to the outdoor grade level
    • and the grade level is above the area outdoors that can receive the greywater.

Limitations on greywater

Greywater cannot be sprayed: Due to the possibility of contamination, a misted greywater could be hazardous. Additionally, the water contains particulates that would almost certainly clog spray nozzles.
Greywater Cannot be stored for more than 24 hours, unless treated for bio hazards.
If spraying or storing is desired, I suggest rainwater catchment. Many homes can harvest as much Rainwater as greywater and rainwater can be sprayed as well as stored as long as desired.

Application:

Greywater must be applied below grade with a minimum of two inches (50mm) of cover over the discharge pipe, even if that two inches of cover is mulch. This means no puddling, no surface greywater should be applied (with some limited exceptions). Greywater must not be allowed to run off the property or into streams, rivers, lakes, or estuaries. Its nutrients become pollutants, but to plants, they are valuable fertilizer.
Your landscape may not always be ready to accept watering when you are producing grey water. For that reason, simple diverter valves are often installed that allow the homeowner to easily switch between yard use and delivery to the sewer/septic system.
Several designs of varying degrees of complexity are available depending on the particular situation and desires of the homeowner.
Is Greywater worth it? Factors to consider:

Negative Factors Positive Factors
Family Size Smaller Larger
Washing Machine style High efficiency Tub type
Outdoor irrigation needs No nearby irrigation needs Trees / vegetable garden
Construction type Slab
(poor shower water accessibility)
Multi-story
with basement or crawl space
Climate Long winters Moderate year round

Configuration:

Drip can be done sub grade in "cans."

You use a 6" dia. valve box at each drip point having an access lid.
I suggest a gravel pit under and around the "box" and the lid 1 or 2" above grade and the box is 6" in height having 4" buried with the dripper in mid elevation in the air inside the box.
The box can be marked non potable or purple in color.

If drippers are used, there must be a sand filter and a 100 micron screening to allow drippers to not plug up.

Glossary for Water Reuse

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Frequently UNasked Questions