Rainwater & Greywater

DBLA specializes in the design of custom rainwater catchment & greywater reuse systems for residential and commercial projects, and we are ready to provide solutions for your site to reduce potable water use, meet storm water treatment requirements, and achieve water independence, resilience and sustainability. 

We have successfully designed numerous systems of various types and scales, and have worked with clients, installers and reviewers to successfully install them and save water. In several jurisdictions, DBLA was the first to achieve permitting for these innovative systems!

We typically design Rainwater harvesting systems for irrigation and/or indoor non-potable uses such as toilet flushing and laundry washing.

Greywater is typically distributed to drip irrigation only.

While these different site-available non-potable water sources are harvested and stored separately, they can be integrated with each other, as well as with municipal potable or recycled water supplies, to provide backup for a continuous water supply to the point of use.

There are various options for automation vs. manual operation, including automatic switchover to backup water, on-demand pressurization, and automatic filter flushing to reduce maintenance requirements.

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

Learn more about our typical design process Here.

In addition to the typical design process described on that page, DBLA typically offers supply and demand calculations and modeling for non-potable water systems in order to estimate the amount of non-potable and backup water that will be used throughout the year, based on long-term monthly averages. This analysis also provides a foundation from which to recommend appropriate storage volumes that maximize non-potable water use while optimizing capacity vs. installation cost.

What Is Rainwater?

Rainwater is clean water that falls freely from the sky onto roofs and landscape surfaces. 

Conventional drainage systems are designed to dispose of rainwater through gutters and pipes, moving it far away as quickly as possible.  Unfortunately, this leads to erosion, flooding, and water pollution problems down the line. 

Meanwhile, significant energy is consumed to import increasingly scarce water from aquifers or reservoirs - sometimes from very far away. This water is treated to potable water standards, often only to be used for irrigation or just literally flushed down the toilet!

Instead, rainwater harvesting (a.k.a. rainwater catchment, collection, reuse, etc.) uses rainwater that falls directly on the site and runs off of roofs during rain storms. Rainwater harvesting systems provide a sustainable alternative to conventional water systems by harvesting, storing, filtering, and using rainwater near where it falls. Rainwater is typically used for non-potable applications that don’t require the water to be treated to potable standards, thereby reducing unnecessary energy spent on treatment and transport.

Rainwater storage may be 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 as potable water (although this can be more of a permitting challenge). 

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. 

Unlike rainwater, which typically only falls during the rainy season, (which is becoming shorter and less reliable here in California) greywater is produced year-round on a daily basis, every time you shower or wash laundry. This, as well as the fact that long-term holding makes greywater less desirable, means that a much smaller volume of greywater needs to be stored vs. rainwater. Therefore, greywater systems can be a cost-effective solution to using site-available water 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.