Graywater Systems

• Laundry-to-Landscaping Pamphlet

Each of us needs to find and practice “new” ways to conserve water as we adapt to looming water scarcity.  Conserving water and lowering your water demand are the first steps.  Re-using non-potable water is another piece of the water conservation toolkit.

CONSERVE FIRST!

Some tips on conserving potable water:

• Purchase water-efficient appliances and low flow toilets, shower heads, faucets and faucet aerators;
• Take short showers and turn off the water when soaping up or shampooing;
• Put a pail under the tub faucet to catch the water when waiting for water to get hot and use this water to water plants and flush toilets;
• Turn off water when brushing teeth and/or shaving;
• Run the dishwasher or washing machine with full loads;
• Use a kitchen dish tub;
• Cover swimming pools;
• Use a broom instead of a hose to clean outdoors;
• Patronize carwashes that recycle water instead of washing your car at home;
• Repair leaks.  Leaks and “running water” (e.g. toilets tanks, hose bibs) accounted for 18% of CA’s fresh water use in 2007.
• Make your garden water-smart:
  • Landscape with CA native and drought tolerant plantings;
  • Landscape without vegetation;
  • Develop rain gardens;
  • Use drip irrigation where possible, use rotors if you use sprinklers.
• Decrease watering in winter months when plant growth slows and turn off irrigation systems in the wet winter months.
• Learn about your daily water use (available on your water bill) or use the Alliance for Water Efficiency’s Water Use Calculator.
• See if you can find ways to save by scheduling a free consultation with Marin Municipal Water District staff.

Graywater

Any water becomes “waste” water once it is dispensed through a faucet. Water from toilets, urinals, kitchen sinks, dishwashers, and laundry loads that include soiled diapers is considered “black” water. Water from bathtubs, showers, bathroom sinks, and washing machines is considered “gray” water. A common re-use of graywater is landscape irrigation.

Graywater systems offer a convenient way to collect, transport and disperse graywater for re-use.

Click on a question to see the answer, or Open All Questions.

• I am looking at buying a piece of raw land. What do I need to do and what is my first step?

  We recommend that you first inspect the site with a private septic systems consultant. Qualified companies and individuals who can perform this service can be found by checking local telephone directories or the Internet.  The consultant you select should be familiar with Marin County codes and requirements.  The consultant should be able to give you at least a rough idea whether or not your plans are feasible. When you are ready to proceed, a consultant can help you apply to Marin County for a site review and percolation tests.

• Why is it easier to use graywater now?

  California graywater regulations changed in August 2009.  The regulations became less stringent and now allow for one type of graywater system, Laundry to Landscape, be installed without permits.

  The regulations are intended to:

  1. Conserve water by facilitating greater reuse of graywater for irrigation.
  2. Reduce the number of noncompliant graywater systems.
  3. Provide guidance and requirements to avoid potentially unhealthful situations.
• Is gardening with graywater safe?

  If guidelines for installation, use, and maintenance of a graywater system are followed, graywater should not present any health or environmental risks.  Micro-organisms in the soil naturally treats graywater as it percolates through the soil by breaking down salts, hair, suspended solids, and organic matter.   The guidelines include: minimizing graywater contact with humans and animals; allowing graywater to percolate through the soil and not run-off the site; preventing graywater from pooling on the surface; not irrigating with graywater edibles with  leafy greens, root crops, or the edible portion of any food crop. 

• How much water will I save?

  The re-use of graywater can decrease potable water use by 16 to 40%, depending on the site, graywater system design, and season.  In a 2012 study of Bay Area homes with graywater irrigation systems, graywater irrigation decreased potable water use an average 26%.  Before installing graywater systems these households were conscious of their water use and used an average 68 gallons per-person-per day, lower than the national average.  Reusing potable water gave these households a way to further save water.

• Will I save money?

  The savings on water bills will have to be balanced with the cost of a graywater system.  Graywater irrigation saves money by enabling more plantings without using more potable water and incurring higher water bills.  Savings will accrue as water shortages and demand force a shift to rates based on actual delivery costs and use.

  Over time, advances in residential treatment systems will allow for toilet flushing and other on-site uses that will decrease residential potable water use.  This will translate into lower bills.

• Can I use graywater to flush?

  Using graywater to flush toilets requires treatment of the graywater to ensure it will not pose a health risk to occupants.  A non-potable water treatment unit for an Owner-Occupied 1-Family residence must meet National Sanitation Foundation (NSF) 350 standards.  Multiple-family dwellings and Commercial/Industrial buildings can only use non-potable water treated to California Code of Regulation Title 22 standards. At this time, there are few NSF350-approved systems for 1-Family owner occupied residences and they can be quite costly.

• What about toilet top sinks?

  Sinks for hand washing that sit atop toilet tanks are not approved for use in California.

Graywater systems are governed by the 2013 California Plumbing Code (CPC), Chapter 16, Non-potable Water Reuse Systems and Marin County Code. The CPC classifies graywater systems based on construction and volume. The classifications and definitions of graywater systems are:

• Clothes Washer System (aka Laundry-to-Landscape) – a graywater system utilizing only a single domestic clothes washing machine in a one- or two-family dwelling that does not include a potable water connection or a pump and does not affect other building, plumbing, electrical, or mechanical components including structural features, egress, fire-life safety, sanitation, potable water supply piping, or accessibility.
• Simple System – a gray water system serving a one- or two-family dwelling with a discharge of 250 gallons (947 liters) per day or less.  Simple systems exceed a clothes washer graywater system. 
• Simple Isolated System – A simple system that does not include a potable water connection or a pump and does not affect other building, plumbing, electrical, or mechanical components including structural features, egress, fire-life safety, sanitation, potable water supply piping, or accessibility.  (This is a graywater system definition unique to Marin County.)
• Complex System – a residential gray water system that discharges over 250 gallons (947 liters) per day.
• On-Site Treated Non-potable Graywater System - a gray water system intended to supply uses such as water closets, urinals, trap primers for floor drains and floor sinks, above and below ground irrigation, and other uses approved by the Authority having Jurisdiction.  (The graywater used in these systems must be treated to minimum water quality requirements.  Please review the California Plumbing Code, Chapter 16.)

In Marin County, clothes washer systems and simple systems are exempt from construction permits. Marin County only requires a notification be filed with EHS for simple graywater systems. A construction permit and plans will be required for complex systems and on-site treated non-potable graywater systems. For graywater systems where the plumbing will be altered or back flow prevention valves are needed, a plumbing permit from the Building and Safety Division may be required.

Complete the applicable notification form or permit application and fee if applicable, and return to EHS.

Determine how much water is needed for irrigation.

• What will be irrigated?
• Is it a seasonal garden?
• Will there be other non-potable water sources such as rainwater harvesting?
• How often do you use your washer and do you launder on a consistent basis? (Graywater cannot be stored.)
• If you produce a large volume of graywater and have a small garden, a graywater system may not be appropriate.

Assess your property and its suitability for a graywater system.

• Is your property located near a water body?  Depending on the type of water body, a 50’-100’ setback is required. 
• Consider the slope of your property.  Are your plantings uphill from your source?  Some systems cannot move water uphill.  On steep downhill slopes, the tubing should be installed in a serpentine (“S”-shape) pattern to slow down the water. 
• Does water drain well where irrigation is needed?  Graywater must not pool on the surface nor run off site.
• Consider erosion.
• Is the location of the clothes washer and/or graywater plumbing exit accessible from your irrigation zone? If it is, a Laundry to Landscape system may work.  The plantings to be irrigated should not be more than 50’ from the machine as the washer’s internal pump is not strong enough to move the water further than that.

New construction vs. a remodel or retrofit?

• If you’re building a new house or doing a full plumbing remodel you may want to combine all your graywater into one line, and use a collection tank and pump to distribute it more widely to your landscape.  (This may be a simple system or a complex system and may require a permit.)
• In retrofit situations it can be very costly to combine all the graywater pipes together.  It may be more practical to plumb each fixture to the closest irrigation zone.

My house has a concrete slab foundation.

• Access to graywater can be lost when pipes enter a concrete slab foundation. If your house is on a concrete foundation, there are still some graywater options:
  1. Laundry-to-Landscape systems enable graywater access without plumbing alterations.
  2. Elevate a tub or shower to access the plumbing.
  3. If there is a second floor, the plumbing is accessible so graywater generated on the second floor can be utilized.

How much graywater is needed for irrigation?

The water demand of your landscape/garden will vary with temperature, rainfall, soil type, and soil drainage.  The water demand is also dependent on the type of soil and how it drains.  A general rule of thumb during peak irrigation season in Marin is ½ gallon per week for each square foot of footprint.  (The footprint is the diameter of the branches and leaves at its widest point).  When calculating, consider microclimates, sun, wind, type of vegetation, season, etc. The San Francisco Graywater Design Manual may be helpful in calculating the water demand.

How much graywater does your household generate?

Consider supply and demand when sizing the graywater system for your home.  The San Francisco Graywater Design Manual has detailed instructions and calculation worksheets to use when calculating the volume of graywater generated in your home. 

Remember to consider periods when graywater will not be generated or needed such as vacations, rainy seasons, and cold weather when plants need less water. Also, future volume may change if the number of occupants or water-use habits in the house change.  Consider when you produce atypical amounts of graywater (e.g., if you sometimes do five loads of laundry in one day rather than spread them out over the week) and consider this when you design and operate your system.

The following are basic calculations for a Laundry to Landscape system:

• 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 typical 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.

Lawn and Graywater

Watering a lawn is not the best use of graywater.  Because graywater cannot be sprayed, lawns may only be irrigated with graywater via subsurface drip emitters located at least two (2) inches below the surface.  Additionally, human and pet contact with graywater is best avoided.  Graywater is best suited for trees and close groupings.

Drip Irrigation with Graywater

All graywater must be discharged under 2” of cover, so drip irrigation must be subsurface.  Filters should be used to remove hair, lint, food, and other particles that may clog the small openings in the drip emitters.  The filters must be cleaned regularly (or back flushed) with clean water.

• Use an automatic filter system and you will not have to remember to clean the filter.
• Drip irrigation requires a pump, electronic controllers, and a back flow prevention device.
• Drip irrigation systems require installation expertise.  They are best for new landscape design because it may be very costly to incorporate drip irrigation into your existing lawn/garden. 

Garden Graywater DO's

• Avoid human and pet contact to minimize potential health risk.
• Distribute water judiciously.
• Water trees (ornamentals and fruit), bushes and flowers first.  Then edibles that are neither leafy greens nor root crops.  It is best to water the edibles with potable water. 
• Irrigate non-acid loving plantings.
• Use irrigation tubing 1-inch in diameter for the main irrigation line; ½-inch tubing to move water from the main line to individual plants in lengths no longer than 2 feet.   Do not go smaller (clogging) or larger (uneven distribution) in size. 
• Discharge graywater to the soil and plantings under a minimum 2-inches of cover material (may include mulch, rock, wood chips, or a solid shield).
• MULCH! Use large wood chips in basins to balance pH; mulch your plants at soil level to retain moisture.

Garden DON'Ts

• Don’t use unfiltered graywater for drip irrigation as it may clog the system.
• Don’t spray irrigate graywater. 
• Don’t put graywater directly on leaves.
• Don’t install an irrigation zone uphill from the washer without appropriate, permitted pumps (no pumps in L2L). 
• Don’t plug or restrict the 1-inch tubing at the furthest outlet of a zone.
• Don’t use ball valves excessively.

Keeping the Soil Healthy

• Irrigate with rainwater or fresh water a few times a year to leach out accumulated salts in the soil.
• Add compost to your soil.
• Use mulch.
• Avoid using chemical pesticides or fertilizers.
• Use plant-friendly products.
• Salts and chlorine bleach can harm soil and plants.

Turn off the Graywater System when...

• Rainy season has begun.
• Washing dirty diapers, anything with chemicals, oily rags.
• If a guest or household member has a communicable disease (e.g., staph infection, hepatitis).
• Using cleaning or personal care products that are harmful to plants (e.g., salts, bleach, harsh cleaners, chemical dyes)
• The water isn't draining well and you see pooling or runoff.
• If you think the plants are receiving too much water.

What Can I Grow With My Graywater System?

Laundry-to-Landscape:

Ornamental and fruit trees, bushes, berry patches (except blueberries), shrubs, large annuals, certain edibles with fruit that grows well off the ground.   NEVER on leafy greens or root crops.

Simple, Complex Systems:

All of the plants listed above for a Laundry-to-Landscape system. Also work well with larger perennials.

Drip Irrigation:

Flower beds, zones with many small plants spread over large areas.  Not the best use for lawns as it can be costly.

Use graywater first on trees, then bushes and flowers, then edibles that are neither leafy greens nor root crops.  If demand exceeds supply, use fresh water on your edibles.

Do Not Irrigate with Graywater

• Acid-loving plants
• Plants that prefer dry conditions
• Root crops, leafy vegetables
• Seedlings, recent transplants, exotics, or plants that are not well established.

• California Plumbing Code (CPC), Chapter 16, Non-potable Water Reuse Systems
• San Francisco Graywater Design Manual
• Alliance for Water Efficiency’s Water Use Calculator
• Marin Municipal Water District Water Survey