Rainwater & Greywater

DBLA has designed numerous custom rainwater catchment & greywater systems for residential and commercial projects, and we are ready to provide solutions for your home or project. 

Contact Us to discuss your project and schedule an initial consultation.

Learn more about our typical design process Here.


What Is Rainwater?

Rainwater is nearly pure water that falls freely onto roofs and landscape surfaces.  Conventionally, it is quickly transferred into gutters and drains, through pipes, and ultimately discharged into streams, rivers, lakes, and the ocean.  Due to increasing development and urbanization pressures, this has led to problems with flooding, erosion, and water pollution. 

As a more sustainable alternative, rainwater harvesting (a.k.a. catchment, collection, etc.) systems store, filter, and re-use rainwater on site.  Rainwater may be saved for use above ground or underground, and tanks come in a variety of sizes, materials, and configurations.  Depending on the system and level of treatment, it can be used for irrigation, toilet flushing, laundry washing, industrial cleaning, fire protection, or even potable water. 

For each 1,000 square feet of impermeable surfaces such as roofs, around 600 gallons of rainwater can be collected per inch of rain, per year.  So a 2,500 sq. ft. building in an area with an average of 16" of rain could expect 24,000 gallons annually.  


What Is Greywater?

Greywater is relatively clean waste water from plumbing fixtures including baths, showers, bathroom/lavatory sinks, laundry washing machines, air conditioner condensate, etc.  Greywater does NOT include sewage from toilets (black water).  Often, kitchen sink water is excluded as well, as it can have a large amount of food waste to be filtered out.   Greywater systems divert the usable water from the waste stream, and can result in a significant, year-round water supply.

Greywater systems require separating the drain pipes of greywater fixtures from sewer pipes, and directing that water to temporary storage, filtration, and use - typically as subsurface or drip irrigation.  Unlike rainwater, greywater should not be stored long term, or used for spray irrigation. It also cannot be used indoors unless it is treated to a higher level to comply with rigorous environmental health standards. 

The California Plumbing Code suggests an estimated production of 40 gallons of greywater per person, per day.  Therefore a family of four might produce nearly 60,000 gallons per year, at least half of which is produced during the dry season when it is most useful for irrigation. 


Integrated Systems

Although rainwater & greywater are very different in terms of their quality and availability, the two systems may complement each other and work together to offset potable water use. While they generally should not be combined in a single tank, one can provide backup for the other, or they can support different end uses. 

For example, a typical integrated system for irrigation might use greywater as the primary source when available, with rainwater providing backup water, and potable water (or another source) as a secondary backup when neither is available.  Alternatively, greywater might be used for irrigation, while rainwater is used to supply indoor non-potable fixtures.  Any given project should be evaluated to determine the feasibility and best use of each water source.


Benefits Of Water Harvesting

  • Provide a water source where utility connections are limited
  • Reduce overall water demand
  • Lower water bills
  • Reduce vulnerability to future water rate increases
  • Be prepared for future drought & restrictions
  • Comply with local water use ordinances (e.g. WELO)
  • Meet stormwater treatment requirements (c.3)
  • Reduce site erosion & flooding problems
  • Help improve infiltration & groundwater replenishment
  • Provide storage for fire protection
  • Reduce energy consumption embedded in potable water
  • Reduce strain on downstream systems
  • Eliminate chlorine from water supply
  • Achieve net-zero water use, green building, or LEED credits