San Jose Residence Case Study 1
Rainwater harvesting system designed by Water Sprout of Oakland, CA.
Rainwater harvesting tank and system components installed by and Bay Maples Landscaping of San Jose, CA
Dual Supply Plumbing Work performed by Energy Upgrade Guys of San Jose, CA
San Jose Residence Case Study 2
With 1,600 square feet of roof area, 3 inches of rain is needed to completely fill the 2,600 gallon cistern. If the cistern is full (total rainfall >3”) and no other rain falls, the family has an 2.31 month supply for toilet flushing and clothes washing.
San Jose Residence Case Study 3
PEX non-potable (purple) pipe is routed to a dedicated angle stop for each toilet and the clothes washer. There are no changes or alterations made to the home's existing potable water supply plumbing.
San Jose Residence Case Study 4
WISY 100 Vortex fine filter removes debris larger than 280 microns and exceeds pre-tank debris screen plumbing code requirement of 1/16” aperture.
San Jose Residence Case Study 5
100 micron sediment filter provides fine sediment filtration before rainwater enters dual plumbing
San Jose Residence Case Study 6
The WaterLab Controller is connected to tank level sensor. When the tank has 6” of rainwater, the controller opens a solenoid valve to let municipal water into the dual plumbing piping through a reduced pressure zone back flow prevention device (RPZ).
San Jose Residence Case Study 7
Non-potable, dual plumbing supply angle stops installed for 1.28 gpf toilet and Energy Star clothes washer.
San Jose Residence Case Study 8
Rainwater samples were analyzed by the Santa Clara County Public Health Laboratory. All samples were below the EPA's maximum allowable water quality standard for E. coli. No samples were taken in January, March, or May 2019.
E. coli is a subgroup of the fecal coliform group. Most E. coli bacteria are harmless and exist in the intestines of people and warm-blooded animals. However, some strains can cause illness. The presence of E. coli in a water sample usually indicates recent fecal contamination. That means there is a greater risk that pathogens are present.
By comparison, when a freshwater swimming area tests more than 100 cfu/100 mL three times in a row, closure of swimming area is required per EPA guidelines.
San Jose Residence Case Study 9
Average indoor use from 3-year water use history provided by San Jose Water Company is 43,833 gallons/year, or 30 gallons/person/day. Rainwater supplied 15% of the family's average indoor water use.
San Jose Residence Case Study 10
Clothes washer and toilets were connected to the rainwater harvesting system on November 1, 2018
With 1600 sq.ft of catchment surface, the 2018/19 rainwater harvesting potential was = 14,067 gallons
2.9” of rain needed to fill cistern
Full cistern = 2.23 month supply
1.3” of rain needed to satisfy average monthly use.
56% of Catchment Potential Used
Note that the 2,600 gallon cistern was able to fulfill April water demand, from March storage when there was little precipitation in April.
San Jose Residence Case Study 11
$0.24/gallon is based on total average annual rainwater use of 7,677 gal (10 ccf) over 20 years
In 2019, San Jose Water Co. delivered water in Tier 1 (indoor use) for $4.7975/ccf
With rainwater supplying 10.5 ccf, annual water bill savings amounts to $50.45/year. The payback period for this system is 755 years.