Greywater System Collection & Re-use

The project re-uses greywater and infiltrates it back into the ground.

• Water from sinks and showers is stored in a 550-gallon greywater tank, treated in a three-stage filtration process, and re-used in the vacuum-flush toilet system. 
• The greywater system was updated when the composting toilet system was replaced with a vacuum-flush system in 2021.

Denis Hayes, the leader behind the Bullitt Center, often compares the building to the Douglas fir forest that once covered the site before settlement by Europeans. With respect to water, the forest would retain, metabolize, and then slowly release the water that falls on its site.

When the composting toilet system was in use (2013-2020), greywater was used solely to recharge the aquifer under the building. With the introduction of a vacuum-flush toilet system, greywater is now treated and used to flush toilets. Greywater is also diverted into the constructed wetland on the third level before being infiltrated into the ground to help recharge the aquifer.

Before greywater is used to flush toilets, it is treated in a three-stage filtration process, followed by a two-stage ultra-violet light disinfection process. The vacuum-flush toilet system uses .4 gallons of treated greywater per flush, which is 70% less water than the average flush toilet.

For greywater diverted to the constructed wetland, it passes through layers of porous gravels and soils. Horsetails, or equisetum, are used as the primary plant for their hardiness and ability to thrive in Seattle’s climate. The water is pumped through a series of drip lines so that the plants can absorb the nutrients. It is then collected and pumped through the system several more times until the nutrients have been absorbed and it is safe to release in the bio-swales along the western edge of the site.

In the bio-swales, the water filters down through 20 feet of gravel before it is deposited into the water table. Functioning similar to the Douglas fir forest, this catch and slow release of water allows the Bullitt Center to restore 61% of the water to the ecosystem either through ground infiltration or evaporation, and mitigate stormwater during and after rain events.

Next building feature: Rainwater Harvesting