Water Types and quality:

Effluent:  Treated water leaving a wastewater treatment plant to be discharged to the bay.

Tertiary Recycled Water:  Water which has been used more than once and has been treated to a "tertiary" level that allows for beneficial reuse. For more information please see the treatment process.

Enhanced Recycled Water:  Recycled water which has been blended with advanced treated water to achieve total dissolved solids (TDS) reductions.

Advanced Treated Water:  Water that has undergone additional treatment beyond tertiary treatment to reduce salts and nutrients to support additional uses, such as irrigation of salt sensitive plants and trees.

Greywater:  Water segregated from a domestic wastewater collection system and reused on site for non-potable purposes.  It can come from showers, bathtubs, washing machines, and bathroom sinks, but not toilets or kitchen sinks.

Groundwater:  Water held underground in the soil or in pores and crevices in rock.  In Palo Alto, we procure the water from sites which are being de-watered for basement construction.



Total Dissolved Solids (TDS) is a measurement of salinity: the amount of salts, ions, minerals per volume of water.  The Palo Alto Regional Water Quality Control Plant aims to produce recycled water with a TDS of 600 mg/L and is moving toward advanced treatment to produce enhanced water with a TDS of approximately 450 mg/L for use on salt-sensitive plants.


Approximate TDS levels:

Rainwater (pure): < 10 ppm

SFPCU "Hetch Hetchy" Palo Alto Municipal Potable drinking water:  100 - 200 ppm

Palo Alto Basement Groundwater (2016 most frequented site - converted from microsiemens): 250 - 375 ppm

Palo Alto Regional Water Quality Control Plant's "enhanced recycled water" (June 2018):  <450 ppm

San Jose (85% Lexington Reservoir/15% Hetch Hetchy):  600 ppm

Palo Alto Regional Water Quality Control Plant's "tertiary" recycled water (current):  800 - 900 ppm

Seawater:  35,000+ ppm


Non-potable reuse: 

Non-potable reuse is the beneficial reuse of recycled/reclaimed water for irrigation, industrial uses, or other non-drinking water purposes.  Existing hard-piped sites must be retrofitted to separate the recycled water pipelines from the potable water pipelines prior to using recycled water.


Purple Pipe Water Services Water Types:

Tertiary Recycled Water:

Palo Alto Regional Water Quality Control Plant's "tertiary" recycled water has been used on almost all plants and grasses successfully for many years.  However, with TDS levels between 800-900ppm, it is a bit saltier than the drinking water supply.  It is not recommended for redwood trees or other salt sensitive plants in large quantities.  If your property has a lot of salt sensitive plants and you're concerned with water quality, you may prefer to have reclaimed groundwater delivered instead.  


Groundwater (Recaptured From Basement De-watering Sites):

Purple Pipe Water Services also procures groundwater from basement de-watering sites in Palo Alto.  The groundwater generally has a lower salt content, but it is not filtered or purified.  The groundwater is tested once when the basement de-watering commences.  Chemical analysis differs a bit at each basement site and, although it is very clear, it may contain suspended solids (extra service fees may apply).  Groundwater salinity tests are done by measuring the electrolyte composition of the water by examining its specific electrical conductance (SEC).  This measures microsiemens content along with pH balance, alkalinity, and Eh (redox potential).  Specific conductance is the measure of the ability of a water conduct electricity.  In general, the higher the concentration of dissolved sales in teh water, the easier it is for electricty to pass through water.  Conductivity is reported in micromhos (umhos) of microSiemens (uS) per centimeter (cm).  Conductivity measurements can be converted to TDS measurements, which are usually reported in parts per million (ppm) by roughly multiplying your umhos/cm or uS/cm by a conversion ratio of 0.66, although this can ratio can go as high as 0.80 depending on the quality of the source.  When converted to TDS levels, the groundwater we use from Palo Alto typically converts to TDS levels in the 250-375 ppm range.


Enhanced Recycled Water (Coming in 2018):

Palo Alto and other nearby cities have already completed projects that have substantially reduced salt levels (as measured by total dissolved solids or "TDS" and parts per million "PPM"), and will continue to plan and implement projects that will further reduce TDS levels.  The Palo Alto Regional Water Quality Control Plant is due to have "enhanced recycled water" by June of 2018.  This is "tertiary" recycled water which will undergo a 4th stage, reverse osmosis.  This water is designed to be used for all landscaping, including redwood trees.  



Please note that Purple Pipe Water Services did not see any real adverse material effects of supplemental recycled water usage - one to two days per week - on any type of plant or grass (including those categorized above as "salt-sensitive") during the 2015 and 2016 watering seasons.

Salt sensitive plants commonly found in the Palo Alto area include redwood trees, citrus trees, and to a lesser extent, roses.  Most of these salt sensitive plants are "acid-loving," meaning that they prefer moist well-drained soil with a pH between 4.5 - 6.0.  Although recycled water is generally considered safe for most types of landscape plants, Purple Pipe Water Services takes special care not to use it on certain species of trees such as redwoods.  However, if you're using tertiary recycled water to supplement your potable-water usage, the potable water leaches out most residual salts in well-draining soils.  Salt accumulation really becomes a problem if you're strictly using recycled water on salt sensitive plants and trees.  A good rule of thumb is to make sure that the TDS levels of the water you're using on your redwood trees and "salt-sensitive" plants is 450 or below.