Rain Gardens


Rain Garden in Hoover Park

Photo: Grassroots Ecology

Rebate Amount: $2.00 per square foot of roof area diverted, maximum of $600
Size: Minimum of 100 square feet of roof diverted

Cost: Varies based on material choices 

Commonly used to divert rainwater from a roof into a garden feature or capture stormwater runoff from impervious surfaces, such as driveways or parking lots.

Must be installed by a licensed contractor.

Receive up to $600 on your rain garden when you apply before installation! 
Applicants can receive a rain garden rebate at a rate of $2.00/square foot up to $600. See table below for details. Applicants can apply for more than one rebate on one property over multiple calendar years. This rebate is a total rebate amount from the City of Palo Alto (City) and Valley Water combined. 

Property Type Pervious Pavement Rebate Rebate Maximum  Palo Alto Lifetime Maximum Valley Water Lifetime Maximum  Total Lifetime Maximum 

$1.50/square foot

($0.75 from Palo Alto and Valley Water, each)

$600  $1,000 $2,000  $3,000 
(includes multi-family properties)
$1.50/square foot
($0.75 from Palo Alto and Valley Water, each)
$600  $5,000  $50,000 $55,000 

Don’t stop at rain gardens! Applicants can receive up to $3,000 on residential properties and $55,000 on commercial properties in a variety of rebates offered by Valley Water and the City. You can browse these options on Valley Water’s Rebate Page.

Frequently Asked Questions

Minimum Criteria for a Rain Garden Rebate
Sizing of the rain garden should be in proportion to the size of the roof area being diverted. Square footage is calculated by the bird’s eye area of the roof where rainwater is actively being diverted. Pitch of roof is not factored into the calculations. To estimate your roof area, refer to this Area Calculator created by Map Developer. This tool allows users to estimate their roof area using satellite imagery on google maps. Refer to the section titled “How to use google maps area calculator to measure your roof” for guidance. While your soil type affects the water infiltration rate and should be amended or replaced as needed, the following table can be used as guidance:

Roof Area Diverted (sq ft) Garden Size (sq ft)
500-700 24
701-900  32 
901-1,100 40 
1,101-1,300 48 
1,301-1,500 56 
1,501-2,000 70 

NOTE: Projects adding roof or other impervious areas more than 2,000 square foot should add 20 square foot of rain garden surface area per every 500 square foot of additional area. Sizing is based on the guidelines prepared by BASMAA, 2012.

  • A minimum of 100 square feet of contributing roof area must be diverted to the rain garden
  • Rain garden must be a minimum of 24 square feet and sized up according to the square footage of the contributing roof area listed in the chart above.
  • The deepest part of the rain garden must be located at least 10 feet from the building foundation, 3 feet from public sidewalks, and 5 feet from private property lines.
  • The garden should not be located over shallow utilities (water, gas, electric) or septic systems or near large trees. Locate utilities before digging by calling Underground Service Alert at 811 or (800)-227-2600.
  • If you plan on moving a large quantity of soil, specifically over 100 cubic yards, you may need a grading permit. Contact the City's Development Center.
  • Simply replacing a downspout with a "rain chain" or just diverting water to flow over the surface of the landscape without creating a designated rain garden will not qualify for a rebate.
  • An overflow area should be incorporated downslope of the rain garden to move excess water away from the building's foundation or neighboring property. The rain garden should not overflow directly into a creek or natural waterway.
  • Rain garden area must be excavated to a minimum depth of 6 inches for puddling. An additional 12 inches of soil beyond the 6 inch excavation must be loosened and amended with 3 inches of compost or replaced with a bioretention soil mix (a mixture of fine compost and mineral aggregate) for heavy clay soils. To maintain an even 6-inch depth, consider using a string level.
  • The excavated rain garden should be covered with a minimum of 2-3 inches of dense mulch or a combination of gravel/river rock to prevent erosion and to minimize weeds.
  • If water enters the garden quickly, include at least 3 feet of gravel or river rock at the entry points to prevent erosion. 

Additional References

  • Rain Garden Rebate Requirements, Valley Water.
    Rain Garden rebates must meet the specifications published here by Valley Water.
  • Rain Garden Fact Sheet, SCVURPPP, 2012
    This resource, provided by the Santa Clara Valley Urban Runoff Pollution Prevention Program, details additional information on the design and maintenance of rain gardens.
  • Coastal California Rain Gardens, University of California, Agricultural and Natural Resources, 2015.
    This guide explains more about the design of rain gardens, as well as information on choosing which plants to use.

Back to the City of Palo Alto Stormwater Rebate Program Homepage