When we started on the project for UCSD Revelle Unit 1, one of our directives was to evaluate a greywater (graywater) system for the dormitories. Greywater is defined as:
a wastewater generated from domestic activities such as laundry, dishwashing, and bathing, which can be recycled on-site for uses such as landscape irrigation and constructed wetlands. Greywater differs from water from the toilets which is designated sewage or blackwater to indicate it contains human waste.
The we studied the feasibility of a Greywater system for the retrofitted buildings as a viable option in reducing water consumption both inside and outside the buildings. In our case we would be looking to irrigate, and flush toilets.
When using Greywater, it is not only a savings of potable water that could be used in a more efficient matter (drinking water), it ends up being a potential cost savings from an energy standpoint. While the cost of the water is not that high right now, $2 per 1000 gallons to treat and deliver (EPA, “How much does it cost to treat and deliver drinking water“, 8/19/2005), this will become a larger issue as our water supplies start to become more limited. This is especially true in Southern California.
One of the hurdles that we came across was the local county Department of Environmental Protection (DEP). They are charged with protection of public water and sewer systems. While Greywater isn’t necessarily a new concept, it is started to get reintroduced into the green vernacular due to LEED and other green initiatives. The county DEP recognized that Greywater was becoming a hot design issue had not developed any initiatives or guidelines for what they would accept for “potential human contact”. So that meant it would default to the stringent standards of potable drinking water.
We then had to look at different treatment systems. We needed to get to a tertiary treatment to have the water come in potential human contact. Other design considerations included, double plumbing the buildings to have separate graywater plumbing that would go to a subsurface holding tank, there, the water would be treated, and then either pumped back up into toilets, or out to a holding tank for irrigation use. As you can imagine, this quickly becomes a logistical challenge with piping mostly inside the building. An existing building would not easily be converted for greywater use. This system needs to be installed and planned before new construction or during a complete renovation.
In evaluating treatment systems, we found that there are several greywater systems for residential development, but very few for larger uses. Australia appears to be ahead of the curve in Greywater systems due to their environmental conditions. One Australian company did have some solutions. Nubian Systems. 
Unfortunately, for this project the costs started to add up due to the size of the project, and the idea was put aside. I hope to see more of these implemented in our designs as prices start to pencil with project costs.
