Frequently Asked Questions

What is an onsite water system?

Onsite water systems take any water from a site, including rainwater, stormwater, greywater, or blackwater, and either reuse it for beneficial use like irrigation, or treat it onsite for ecological disposal, like a septic system.  California spends billions of dollars and kilojoules of energy annually to treat and transport water to our points of use.  Then it gets flushed away and we pay to transport it and treat it… again.  Repurposing onsite water not only saves water, it decreases the load on our sewer treatment infrastructure.  It also allows that water to filter naturally and infiltrate back into the groundwater aquifers which increases water security and beneficially affects our environment.

How does Greywater irrigation work?   

Greywater is water sourced from bathroom sinks, showers, tubs, and washing machines and recycled for irrigation of outside landscaping.

Greywater does not include water that has come in contact with feces or dirty diaper wash-water.  In California, kitchen sink and dishwasher water are also not permitted in greywater systems. Greywater should be piped to subsurface irrigation outlets to prevent the potential spread of contaminants.  Greywater works best where it can be directly gravity fed and should not be stored for more than 24 hours.  For more information visit

How does Rainwater harvesting work?  

Rainwater catchment systems collect and store water sourced from roof structures.  Even sites in arid locations can generate relatively large volumes of water from rain catchment.  For instance, a 2,000-square foot structure that receives 12 inches of rain annually could capture almost 15,000 gallons per year.  Potential uses for rainwater include: toilet flushing, laundry, irrigation, fire protection and more.  It should not be used as potable water without proper filtration and treatment.

Rainwater systems have the lowest installation cost where there is a relatively short dry season because the size of the storage tanks can be comparably smaller. Although in most of California larger storage tanks are generally required, rainwater can still make sense where water is scarce.  It is often utilized where wells have failed or become contaminated or the cost of water is otherwise high.

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How does Stormwater catchment work?

Stormwater systems are principally used to prevent flooding, erosion and contamination of chemical or environmental pollutants.  They are also used to recharge local groundwater aquafers or wetlands.  The idea is to slow the water down to contain water when it is a liability so it can be utilized when it is scarce.  Usually, the water is channeled to a depression over permeable soil called an infiltration basin or rain garden, but it can also be channeled to catchment ponds for landscape or agricultural irrigation.

These systems are best utilized where roofs, parking lots and other impermeable hardscapes prevent natural infiltration or where industrial areas juxtapose sensitive environmental areas.  A simple inexpensive example would be to add a curb cut to allow water from a parking lot to enter a planter bed.  Best management practice provides for a channel to allow an oversaturated system to overflow back into the existing drainage.

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Is onsite water safe? 

Yes.  As with any water management system there is always some risk of contamination.  But when the systems are designed and maintained properly, the risk is low.  Blackwater (septic) systems requirements are well established and time tested.  Soil has an amazing ability to filter and purify water naturally without chemical additives or high energy inputs.  Greywater irrigation systems can be safely used within as little as three feet from the water table.  California requires subsurface greywater delivery systems.  The purity of rainwater cisterns generally tests very good.  It can safely be used for irrigation and residential toilet flushing.  However, because of the possibility of exposure to bird and animal feces from the roofs and conveyances, proper filtration and UV or chemical treatment are necessary to make it safe for potable use.

Proximity setbacks, municipal codes and common sense should always be observed.  

  Is onsite water legal? 

Yes.  However, regulation is in place for most applications.  The simplest systems such as laundry to landscape greywater systems generally do not even require a permit.  In other situations, onsite water systems may be completely restricted or required.  Factors that affect regulation include: site location, governing jurisdiction/s, whether it is intended for commercial, industrial or residential use, proximity to well or waterways, size of the system etc.  To determine the requirements for your application, contact your local building department or Public Health administration.

Is onsite water expensive? 

The cost is highly variable.  No one water technology is appropriate for every location.  However, in many cases onsite water systems are the least expensive option in the long run especially in off-grid locations or where utility costs are high.  To determine direct cost comparison, make sure you are considering all the quantifiable factors such as system construction and maintenance, current and projected water and energy usage and rates.  In some cases, grants or incentives are available to offset installation costs.

Don’t forget to also consider the many indirect benefits of onsite water systems.  For example, this could include increased water security, flooding and erosion control, availability of water for fire suppression, environmental sustainability etc.

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