Graywater systems

How much water do you need?

• What will be irrigated?
• Is it a seasonal need?
• Will you have other non-potable water sources like stored rainwater?
• How often do you use your washer? It is unsafe to store graywater.
• If you have a small garden but produce lots of wastewater, a graywater system may not be your best option.

Assess your property and its suitability for a graywater system

• Is your property located near a body of water? Sometimes you need a 50’-100’ setback in these situations. 
• Are your plantings uphill from your source? Some systems cannot move water uphill. On steep downhill slopes, you need space for a serpentine (“S”-shape) pattern to slow down the water. 
• Graywater should not pool on the surface or run off the site. Does your soil absorb water well?
• Do you have erosion concerns?
• Are you able to access your clothes washer or graywater plumbing? Can you reach your irrigation zone? Is your irrigation zone too far away? Systems that use the washing machine's internal pump have a 50' limit.

New construction vs. a remodel or retrofit

• New construction and a full plumbing remodel gives you extra options. You can combine all graywater into one line. A collection tank and pump can help you distribute water further. Be sure to get a permit.
• When adding your system to an existing home, you have less flexibility. It may be easier to send water from each fixture direct to irrigation zones.

My house has a concrete slab foundation

• You have fewer options when your house is on a concrete slab foundation. But you still have options!
  • "Laundry-to-Landscape" systems collect graywater without plumbing alterations.
  • You can elevate a tub or shower to access the plumbing.
  • You can collect graywater from a higher floor. A second floor source can make access to plumbing easier.

1. Graywater discharge must be under at least 2 inches of approved cover such as mulch, soil, or gravel. 
2. Check if your system needs a valve to divert flows back to the building sewer or septic system.
3. Graywater must not pool or runoff. It cannot flow to a neighboring property.
4. Graywater disposal fields/mulch basins must be at least 5 feet from the property line. And  at least 100 feet from wells and waterways. 
5. More information in the graywater notification form. Chapter 15 of the California Plumbing Code is also a good resource. 

How much graywater is needed for irrigation?

Water needs vary:

• Season, microclimates, wind, sun, and rainfall
• Soil and drainage
• Plant choice
• A rule of thumb for Marin in summer is a 1/2 gallon per square foot of footprint. Footprint is the circle that contains the branches and leaves of your plants.
• The San Francisco Graywater Design Manual has tips for this.

How much graywater does your household generate?

• The San Francisco Graywater Design Manual can help calculate the volume of graywater you generate in your home. 
• You generate less when you have time away. You need less when it rains or the temperature drops. 
• You may generate more wastewater in the future. Remember the summer months. A new addition to the family? 
• Plan for special situations. Do you ever do 5 loads of laundry on some special days? These special situations affect your design.

Washing machines (weekly flow):

___ gallons/load (your machine’s rating)  X ___ loads per week = ___ gallons per week.

Washing machines (daily flow):

___ gallons/load (your machine’s rating)  X ___ loads per laundry day =___ gallons per typical laundry day.

Showers:

___ gallons per minute (your showerhead flow rate ) X ___ minutes you shower X
___ showers per day X ___ actual number of home occupants = ___ gallons per day.