New Greywater Report: Greyt Potential!

November 24, 2010 § Leave a comment

Pacific Institute's Overview of Greywater Reuse report - November 2010 - click to download 41-page pdf

Earlier this week, Los Angeles Times Greenspace tipped L.A. Creek Freak off to a new greywater report from the Pacific Institute. The new report is titled Overview of Greywater Reuse: the Potential of Greywater Systems to Aid Sustainable Water Management, released this month – November 2010. It’s available as a pdf download here.

If you’re not at all familiar with greywater, it refers to water from washing machines, sinks, bathtubs, etc. which isn’t clean enough to drink, but can be used to water landscaping. For some basic greywater background, read this article or watch this video.

The 41-page report is very clear and readable, with plenty of case studies from simple to somewhat complex. The report is international in scope, empasizing greywater’s potential to offset potable water use. It has some emphasis on systems in the Middle East and Africa, but the information is very applicable to Southern California, too. Quoting from the intro:

When greywater is reused either onsite or nearby, it has the potential to reduce the demand for new water supply, reduce the energy and carbon footprint of water services, and meet a wide range of social and economic needs. In particular, the reuse of greywater can help reduce demand for more costly high-quality potable water.

It breaks down greywater systems into three types – in order of ascending complexity and cost:

  1. Greywater Diversion Systems: basic direct home to yard immediate reuse systems, with no storage [this includes the quick cheap greywater hook-up that this Creek Freak uses, knows and loves!]
  2. Physical Greywater Treatment Systems: systems that filter and disinfect greywater and store it for later use
  3. Biological Greywater Treatment Systems:  systems that use biological water processing technologies to treat greywater to more-or-less potable water standards

The report touches on some debates as to greywater reuse’s impacts on wastewater (sewage) systems. While I feel pretty confident that systems like mine do help reduce energy input to treat sewage (and to import/pump potable water to L.A.), there’s also some concern that:

…diversion of greywater could potentially be disruptive to wastewater collection and treatment, as a lower volume of wastewater would be diverted for treatment, and it would contain a higher concentration of contaminants and solids. In pipes with low slopes, this could potentially lead to insufficient flows in sewers to carry waste to the treatment plant.

I guess if we divert too much water, at some point there might not be enough flow to carry the rest of the sewage… Famous  last words, but I think that, for Southern California, given current levels of greywater use, this problem could be a long way off.

Average Indoor Water Use for North American Cities - from page 26 of Pacific Institute Greywater Reuse report

The report has interesting estimates on just how much water is available for greywater diversion:

The percentage of household water that is greywater varies regionally and between households, depending on the primary uses of water in a home and how efficiently water is used, but is generally between 50% and 80%. … In the United States, greywater comprises up to 50% of single family household use (Sheikh 2010)

For Southern California, I’ve heard it stated that approximately two-thirds of our water use is outdoors. Think lawns. Unfortunately, it’s somewhat difficult to get basic greywater systems to evenly disperse water over a broad area such as a lawn. If we get all that available indoor water (50%) out and reuse it on our landscape, we offset a lot of water, but we’ll still need to change our landscape to need less water. Think fewer lawns.

The report gives an optimistic prognosis for greywater reuse as one very worthwhile tool in moving toward sustainability and resilience. From the conclusion:

In many places around the world, increasing demands on freshwater and the impacts of climate change on water availability are reducing the security of water access. Globally, many regions have reached a point at which existing water resources are already being over-used, as evidenced by the depletion of groundwater aquifers and rivers which no longer reach the sea. Many new water sources will require that societies go further and pay more to access water. But limitations in water availability can also lead to the more efficient use of water, better management of existing resources, and increases in the resource productivity of a single unit of water.

Greywater reuse is a promising strategy in terms of the significant local water, energy, and cost savings that it can produce. Small demonstration projects and new, more flexible, greywater policies have demonstrated the successful use of greywater at multiple scales.

The report goes on to end with a series of recommendations – from research to financing to learning exchanges. It’s worth a read – download Overview of Greywater Reuse: the Potential of Greywater Systems to Aid Sustainable Water Management here.


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